Scarce 1954 Robert Oppenheimer Vintage Original Photo Physics Famous Scientist

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Seller: memorabilia111 ✉️ (807) 100%, Location: Ann Arbor, Michigan, US, Ships to: US & many other countries, Item: 176260300001 SCARCE 1954 ROBERT OPPENHEIMER VINTAGE ORIGINAL PHOTO PHYSICS FAMOUS SCIENTIST. There, he stimulated discussion and research on quantum and relativistic physics in the School of Natural Sciences. 1963 Dec 2nd Received the Enrico Fermi Award. Physical theories can be grouped into three categories: mainstream theories, proposed theories and fringe theories. A VINTAGE ORIGINAL 7 1/4 X 10 INCH PHOTO FROM 1954 OF ROBERT OPPENHEIMER _________________________________________________________________________________________________________ J. Robert Oppenheimer[note 1] (/ˈɒpənˌhaɪmər/; April 22, 1904 – February 18, 1967) was an American theoretical physicist. Oppenheimer served as the director of the Los Alamos Laboratory during World War II, and is often credited as the "father of the atomic bomb" for his role in the Manhattan Project, the research and development undertaking that created the world's first-ever nuclear weapons. Oppenheimer attended Harvard University, where he earned a bachelor's degree in chemistry in 1925, and went on to study physics at the University of Cambridge and University of Göttingen, where he received his PhD in 1927. After completing his education, he held academic positions at the University of California, Berkeley, and the California Institute of Technology (Caltech), and made significant contributions to theoretical physics, including in quantum mechanics and nuclear physics. During World War II, he was recruited to work on the Manhattan Project, and in 1943 was appointed as director of the Los Alamos Laboratory in New Mexico, tasked with developing the weapons. Oppenheimer's leadership and scientific expertise were instrumental in the success of the project. He was among those who observed the Trinity test on July 16, 1945, in which the first atomic bomb was successfully detonated. He later remarked that the explosion brought to his mind words from the Hindu scripture Bhagavad Gita: "Now I am become Death, the destroyer of worlds."[2][note 2] In August 1945, the atomic bombs were used on the Japanese cities of Hiroshima and Nagasaki, which to date remains the only use of nuclear weapons in war. After the war ended, Oppenheimer became chairman of the influential General Advisory Committee of the newly created United States Atomic Energy Commission. He used that position to lobby for international control of nuclear power, to avert nuclear proliferation and a nuclear arms race with the Soviet Union. He opposed the development of the hydrogen bomb during a 1949–1950 governmental debate on the question and subsequently took stances on defense-related issues that provoked the ire of some U.S. government and military factions. During the Second Red Scare, those stances, together with past associations Oppenheimer had with people and organizations affiliated with the Communist Party, led to the revocation of his security clearance in a much-written-about hearing in 1954. Effectively stripped of his direct political influence, he continued to lecture, write, and work in physics. Nine years later, President John F. Kennedy awarded him (and Lyndon B. Johnson presented him with) the Enrico Fermi Award as a gesture of political rehabilitation. In 2022, five decades after his death, the U.S. government formally nullified its 1954 decision and affirmed Oppenheimer's loyalty.[3][4] Oppenheimer's achievements in physics include the Born–Oppenheimer approximation for molecular wave functions, work on the theory of electrons and positrons, the Oppenheimer–Phillips process in nuclear fusion, and the first prediction of quantum tunneling. With his students he also made important contributions to the modern theory of neutron stars and black holes, as well as to quantum mechanics, quantum field theory, and the interactions of cosmic rays. As a teacher and promoter of science, he is remembered as a founding father of the American school of theoretical physics that gained world prominence in the 1930s. After World War II, he became director of the Institute for Advanced Study in Princeton, New Jersey. Early life Childhood and education J. Robert Oppenheimer was born into a Jewish family in New York City on April 22, 1904,[note 1][5] to Ella (née Friedman), a painter, and Julius Seligmann Oppenheimer, a wealthy textile importer. Julius was born in Hanau, then part of the Hesse-Nassau province of the Kingdom of Prussia, and came to the United States as a teenager in 1888 with few resources, no money, no baccalaureate studies, and no knowledge of the English language. He was hired by a textile company and within a decade was an executive there, eventually becoming wealthy.[6] Oppenheimer's family were nonobservant Jews.[7] In 1912, the family moved to an apartment on the 11th floor of 155 Riverside Drive, near West 88th Street, Manhattan, an area known for luxurious mansions and townhouses.[5] Their art collection included works by Pablo Picasso and Édouard Vuillard, and at least three original paintings by Vincent van Gogh.[8] Robert had a younger brother, Frank, who also became a physicist, and who later founded the Exploratorium science museum in San Francisco.[9] Oppenheimer was initially educated at Alcuin Preparatory School; in 1911, he entered the Ethical Culture Society School.[10] This had been founded by Felix Adler to promote a form of ethical training based on the Ethical Culture movement, whose motto was "Deed before Creed". His father had been a member of the Society for many years, serving on its board of trustees from 1907 to 1915.[11] Oppenheimer was a versatile scholar, interested in English and French literature, and particularly in mineralogy.[12] He completed the third and fourth grades in one year and skipped half of the eighth grade.[10] During his final year, he became interested in chemistry.[13] He graduated in 1921 and entered Harvard College one year later, at age 18, because he suffered an attack of colitis while prospecting in Joachimstal during a family summer vacation in Europe. To help him recover from the illness, his father enlisted the help of his English teacher Herbert Smith, who took him to New Mexico, where Oppenheimer fell in love with horseback riding and the southwestern United States.[14] Oppenheimer majored in chemistry, but Harvard required science students to also study history, literature, and philosophy or mathematics. He compensated for his late start by taking six courses each term and was admitted to the undergraduate honor society Phi Beta Kappa. In his first year, he was admitted to graduate standing in physics on the basis of independent study, which meant he was not required to take the basic classes and could enroll instead in advanced ones. He was attracted to experimental physics by a course on thermodynamics taught by Percy Bridgman. In 1925, after three years of study, Oppenheimer graduated with a Bachelor of Arts degree summa cum laude.[15] Studies in Europe Fifteen men in suits, and one woman, pose for a group photograph Heike Kamerlingh Onnes' Laboratory in Leiden, Netherlands, 1926. Oppenheimer is in the middle row, second from the left. In 1924, Oppenheimer was informed that he had been accepted into Christ's College, Cambridge. He wrote to Ernest Rutherford requesting permission to work at the Cavendish Laboratory. Bridgman provided Oppenheimer with a recommendation, which conceded that Oppenheimer's clumsiness in the laboratory made it apparent his forte was not experimental but rather theoretical physics. Rutherford was unimpressed, but Oppenheimer went to Cambridge in the hope of landing another offer.[16] He was ultimately accepted by J. J. Thomson on condition that he complete a basic laboratory course.[17] He developed an antagonistic relationship with his tutor, Patrick Blackett, who was only a few years his senior. While on vacation, as recalled by his friend Francis Fergusson, Oppenheimer once confessed that he had left an apple doused with noxious chemicals on Blackett's desk. While Fergusson's account is the only detailed version of this event, Oppenheimer's parents were alerted by the university authorities who considered placing him on probation, a fate prevented by his parents successfully lobbying the authorities.[18] Oppenheimer was a tall, thin chain smoker,[19] who often neglected to eat during periods of intense thought and concentration. Many of his friends said he had self-destructive tendencies. A disturbing event occurred when he took a vacation from his studies in Cambridge to meet up with Fergusson in Paris. Fergusson noticed that Oppenheimer was not well. To help distract him from his depression, Fergusson told Oppenheimer that he (Fergusson) was to marry his girlfriend, Frances Keeley. Oppenheimer did not take the news well. He jumped on Fergusson and tried to strangle him. Although Fergusson easily fended off the attack, the episode convinced him of Oppenheimer's deep psychological troubles. Throughout his life, Oppenheimer was plagued by periods of depression,[20][21] and he once told his brother, "I need physics more than friends".[22] In 1926, Oppenheimer left Cambridge for the University of Göttingen to study under Max Born. Göttingen was one of the world's leading centers for theoretical physics. Oppenheimer made friends who went on to great success, including Werner Heisenberg, Pascual Jordan, Wolfgang Pauli, Paul Dirac, Enrico Fermi and Edward Teller. He was known for being too enthusiastic in discussion, sometimes to the point of taking over seminar sessions.[23] This irritated some of Born's other students so much that Maria Goeppert presented Born with a petition signed by herself and others threatening a boycott of the class unless he made Oppenheimer quiet down. Born left it out on his desk where Oppenheimer could read it, and it was effective without a word being said.[24] Oppenheimer obtained his Doctor of Philosophy degree in March 1927 at age 23, supervised by Born.[25] After the oral exam, James Franck, the professor administering, reportedly said, "I'm glad that's over. He was on the point of questioning me."[26] Oppenheimer published more than a dozen papers while in Europe, including many important contributions to the new field of quantum mechanics. He and Born published a famous paper on the Born–Oppenheimer approximation, which separates nuclear motion from electronic motion in the mathematical treatment of molecules, allowing nuclear motion to be neglected to simplify calculations. It remains his most cited work.[27] Early career Educational work Oppenheimer was awarded a United States National Research Council fellowship to the California Institute of Technology (Caltech) in September 1927. Bridgman also wanted him at Harvard, so a compromise was reached whereby he split his fellowship for the 1927–28 academic year between Harvard in 1927 and Caltech in 1928.[28] At Caltech he struck up a close friendship with Linus Pauling, and they planned to mount a joint attack on the nature of the chemical bond, a field in which Pauling was a pioneer, with Oppenheimer supplying the mathematics and Pauling interpreting the results. Both the collaboration and their friendship ended when Pauling began to suspect Oppenheimer of becoming too close to his wife, Ava Helen Pauling. Once, when Pauling was at work, Oppenheimer had arrived at their home and invited Ava Helen to join him on a tryst in Mexico. Though she refused and reported the incident to her husband,[29] the invitation, and her apparent nonchalance about it, disquieted Pauling and he ended his relationship with Oppenheimer. Oppenheimer later invited him to become head of the Chemistry Division of the Manhattan Project, but Pauling refused, saying he was a pacifist.[30] In the autumn of 1928, Oppenheimer visited Paul Ehrenfest's institute at the University of Leiden, the Netherlands, where he impressed by giving lectures in Dutch, despite having little experience with the language. There he was given the nickname of Opje,[31] later anglicized by his students as "Oppie".[32] From Leiden he continued on to the Swiss Federal Institute of Technology (ETH) in Zurich to work with Wolfgang Pauli on quantum mechanics and the continuous spectrum. Oppenheimer respected and liked Pauli and may have emulated his personal style as well as his critical approach to problems.[33] Greek style buildings and a clock tower The University of California, Berkeley, where Oppenheimer taught from 1929 to 1943 On returning to the United States, Oppenheimer accepted an associate professorship from the University of California, Berkeley, where Raymond T. Birge wanted him so badly that he expressed a willingness to share him with Caltech.[30] Before he began his Berkeley professorship, Oppenheimer was diagnosed with a mild case of tuberculosis and spent some weeks with his brother Frank at a New Mexico ranch, which he leased and eventually purchased. When he heard the ranch was available for lease, he exclaimed, "Hot dog!", and later called it Perro Caliente, literally "hot dog" in Spanish.[34] Later he used to say that "physics and desert country" were his "two great loves".[35] He recovered from tuberculosis and returned to Berkeley, where he prospered as an advisor and collaborator to a generation of physicists who admired him for his intellectual virtuosity and broad interests. His students and colleagues saw him as mesmerizing: hypnotic in private interaction, but often frigid in more public settings. His associates fell into two camps: one saw him as an aloof and impressive genius and aesthete, the other as a pretentious and insecure poseur.[36] His students almost always fell into the former category, adopting his walk, speech, and other mannerisms, and even his inclination for reading entire texts in their original languages.[37] Hans Bethe said of him: Probably the most important ingredient he brought to his teaching was his exquisite taste. He always knew what were the important problems, as shown by his choice of subjects. He truly lived with those problems, struggling for a solution, and he communicated his concern to the group. In its heyday, there were about eight or ten graduate students in his group and about six Post-doctoral Fellows. He met this group once a day in his office and discussed with one after another the status of the student's research problem. He was interested in everything, and in one afternoon they might discuss quantum electrodynamics, cosmic rays, electron pair production and nuclear physics.[38] Oppenheimer worked closely with Nobel Prize-winning experimental physicist Ernest O. Lawrence and his cyclotron pioneers, helping them understand the data their machines were producing at the Lawrence Berkeley National Laboratory.[39] In 1936, Berkeley promoted him to full professor at a salary of $3,300 a year (equivalent to $70,000 in 2022). In return he was asked to curtail his teaching at Caltech, so a compromise was reached whereby Berkeley released him for six weeks each year, enough to teach one term at Caltech.[40] Scientific work Oppenheimer did important research in theoretical astronomy (especially as related to general relativity and nuclear theory), nuclear physics, spectroscopy, and quantum field theory, including its extension into quantum electrodynamics. The formal mathematics of relativistic quantum mechanics also attracted his attention, although he doubted its validity. His work predicted many later finds, which include the neutron, meson and neutron star.[41] Initially, his major interest was the theory of the continuous spectrum and his first published paper, in 1926, concerned the quantum theory of molecular band spectra. He developed a method to carry out calculations of its transition probabilities. He calculated the photoelectric effect for hydrogen and X-rays, obtaining the absorption coefficient at the K-edge. His calculations accorded with observations of the X-ray absorption of the sun, but not helium. Years later it was realized that the sun was largely composed of hydrogen and that his calculations were indeed correct.[42][43] Einstein writing at a desk. Oppenheimer sits beside him, looking on. Physicists Albert Einstein and Oppenheimer conferring circa 1950 Oppenheimer also made important contributions to the theory of cosmic ray showers and started work that eventually led to descriptions of quantum tunneling. In 1931, he co-wrote a paper on the "Relativistic Theory of the Photoelectric Effect" with his student Harvey Hall,[44] in which, based on empirical evidence, he correctly disputed Dirac's assertion that two of the energy levels of the hydrogen atom have the same energy. Subsequently, one of his doctoral students, Willis Lamb, determined that this was a consequence of what became known as the Lamb shift, for which Lamb was awarded the Nobel Prize in physics in 1955.[41] With his first doctoral student, Melba Phillips, Oppenheimer worked on calculations of artificial radioactivity under bombardment by deuterons. When Ernest Lawrence and Edwin McMillan bombarded nuclei with deuterons they found the results agreed closely with the predictions of George Gamow, but when higher energies and heavier nuclei were involved, the results did not conform to the theory. In 1935, Oppenheimer and Phillips worked out a theory—now known as the Oppenheimer–Phillips process—to explain the results; this theory is still in use today.[45] As early as 1930, Oppenheimer wrote a paper that essentially predicted the existence of the positron. This was after a paper by Paul Dirac proposed that electrons could have both a positive charge and negative energy. Dirac's paper introduced an equation, known as the Dirac equation, that unified quantum mechanics, special relativity and the then-new concept of electron spin, to explain the Zeeman effect.[46] Oppenheimer, drawing on the body of experimental evidence, rejected the idea that the predicted positively charged electrons were protons. He argued that they would have to have the same mass as an electron, whereas experiments showed that protons were much heavier than electrons. Two years later, Carl David Anderson discovered the positron, for which he received the 1936 Nobel Prize in Physics.[47] In the late 1930s, Oppenheimer became interested in astrophysics, most likely through his friendship with Richard Tolman, resulting in a series of papers. In the first of these, a 1938 paper co-written with Robert Serber titled "On the Stability of Stellar Neutron Cores",[48] Oppenheimer explored the properties of white dwarfs. This was followed by a paper co-written with one of his students, George Volkoff, "On Massive Neutron Cores",[49] in which they demonstrated that there was a limit, the so-called Tolman–Oppenheimer–Volkoff limit, to the mass of stars beyond which they would not remain stable as neutron stars and would undergo gravitational collapse. Finally, in 1939, Oppenheimer and another of his students, Hartland Snyder, produced the paper "On Continued Gravitational Contraction",[50] which predicted the existence of what are today known as black holes. After the Born–Oppenheimer approximation paper, these papers remain his most cited, and were key factors in the rejuvenation of astrophysical research in the United States in the 1950s, mainly by John A. Wheeler.[51] Oppenheimer's papers were considered difficult to understand even by the standards of the abstract topics he was expert in. He was fond of using elegant, if extremely complex, mathematical techniques to demonstrate physical principles, though he was sometimes criticized for making mathematical mistakes, presumably out of haste. "His physics was good", said his student Snyder, "but his arithmetic awful".[41] After World War II, Oppenheimer published only five scientific papers, one of which was in biophysics, and none after 1950. Murray Gell-Mann, a later Nobelist who, as a visiting scientist, worked with him at the Institute for Advanced Study in 1951, offered this opinion: He didn't have Sitzfleisch, "sitting flesh," when you sit on a chair. As far as I know, he never wrote a long paper or did a long calculation, anything of that kind. He didn't have patience for that; his own work consisted of little aperçus, but quite brilliant ones. But he inspired other people to do things, and his influence was fantastic.[52] Private and political life During the 1920s, Oppenheimer remained uninformed on worldly matters. He claimed that he did not read newspapers or popular magazines and only learned of the Wall Street crash of 1929 while he was on a walk with Ernest Lawrence six months after the crash occurred.[53][54] He once remarked that he never cast a vote until the 1936 presidential election. From 1934 on, however, he became increasingly concerned about politics and international affairs. In 1934, he earmarked three percent of his annual salary—about $100 (equivalent to $2,188 in 2022)—for two years to support German physicists fleeing Nazi Germany. During the 1934 West Coast Waterfront Strike, he and some of his students, including Melba Phillips and Bob Serber, attended a longshoremen's rally. Oppenheimer repeatedly attempted to get Serber a position at Berkeley but was blocked by Birge, who felt that "one Jew in the department was enough".[55] Mug shot with "K-6" over it and "J. R. Oppenheimer" typewritten below. Oppenheimer's ID badge from the Los Alamos Laboratory Oppenheimer's mother died in 1931, and he became closer to his father who, although still living in New York, became a frequent visitor in California.[56] When his father died in 1937, leaving $392,602 to be divided between Oppenheimer and his brother Frank, Oppenheimer immediately wrote out a will that left his estate to the University of California to be used for graduate scholarships.[57] Like many young intellectuals in the 1930s, Oppenheimer supported social reforms that were later alleged to be communist ideas. He donated to many progressive causes that were branded as left-wing during the McCarthy era. The majority of his allegedly radical work consisted of hosting fundraisers for the Republican cause in the Spanish Civil War and other anti-fascist activity. He never openly joined the Communist Party USA (CPUSA), though he did pass money to leftist causes by way of acquaintances who were alleged to be party members.[58] When he joined the Manhattan Project in 1942, Oppenheimer wrote on his personal security questionnaire that he had been "a member of just about every Communist Front organization on the West Coast".[59] Years later he claimed that he did not remember saying this, that it was not true, and that if he had said anything along those lines, it was "a half-jocular overstatement".[60] He was a subscriber to the People's World,[61] a Communist Party organ, and he testified in 1954, "I was associated with the communist movement."[62] From 1937 to 1942, Oppenheimer was a member at Berkeley of what he called a "discussion group", which was later identified by fellow members Haakon Chevalier[63][64] and Gordon Griffiths as a "closed" (secret) unit of the Communist Party for Berkeley faculty.[65] The FBI opened a file on Oppenheimer in March 1941. It recorded that he attended a meeting in December 1940 at Chevalier's home that was also attended by the Communist Party's California state secretary, William Schneiderman, and its treasurer, Isaac Folkoff. The FBI noted that Oppenheimer was on the Executive Committee of the American Civil Liberties Union, which it considered a communist front organization. Shortly thereafter, the FBI added Oppenheimer to its Custodial Detention Index, for arrest in case of national emergency.[66] Debates over Oppenheimer's party membership or lack thereof have turned on very fine points; almost all historians agree he had strong left-wing views during this time and interacted with party members, though there is considerable dispute over whether he was officially a member of the party. At his 1954 security clearance hearings, he denied being a member of the Communist Party but identified himself as a fellow traveler, which he defined as someone who agrees with many of the goals of communism but is not willing to blindly follow orders from any Communist Party apparatus.[67] In August 1943, he volunteered to Manhattan Project security agents that George Eltenton, whom he did not know, had solicited three men at Los Alamos for nuclear secrets on behalf of the Soviet Union. When pressed on the issue in later interviews, Oppenheimer admitted that the only person who had approached him was his friend Haakon Chevalier, a Berkeley professor of French literature, who had mentioned the matter privately at a dinner at Oppenheimer's house.[68] Brigadier General Leslie R. Groves, Jr., the director of the Manhattan Project, thought Oppenheimer too important to the project to be ousted over this suspicious behavior. On July 20, 1943, he wrote to the Manhattan Engineer District: In accordance with my verbal directions of July 15, it is desired that clearance be issued to Julius Robert Oppenheimer without delay irrespective of the information which you have concerning Mr Oppenheimer. He is absolutely essential to the project.[69] Relationships and children In 1936, Oppenheimer became involved with Jean Tatlock, the daughter of a Berkeley literature professor and a student at Stanford University School of Medicine. The two had similar political views; she wrote for the Worker, a Communist Party newspaper.[70] In 1939, after a tempestuous relationship, Tatlock broke up with Oppenheimer. In August of that year, he met Katherine ("Kitty") Puening, a radical Berkeley student and former Communist Party member. Kitty had been married before. Her first marriage lasted only a few months. Her second, common-law marriage husband was Joe Dallet, an active member of the Communist Party, who was killed in the Spanish Civil War.[71] Kitty returned to the United States, where she obtained a Bachelor of Arts degree in botany from the University of Pennsylvania. There she married Richard Harrison, a physician and medical researcher, in 1938. In June 1939 Kitty and Harrison moved to Pasadena, California, where he became chief of radiology at a local hospital and she enrolled as a graduate student at the University of California, Los Angeles. Oppenheimer and Kitty created a minor scandal by sleeping together after one of Tolman's parties. In the summer of 1940, she stayed with Oppenheimer at his ranch in New Mexico. She finally asked Harrison for a divorce when she found out she was pregnant. When he refused, she obtained an instant divorce in Reno, Nevada, and took Oppenheimer as her fourth husband on November 1, 1940.[72] Their first child, Peter, was born in May 1941,[73] and their second, Katherine ("Toni"), was born in Los Alamos, New Mexico, on December 7, 1944.[72] During his marriage, Oppenheimer rekindled his affair with Tatlock.[74] Later their continued contact became an issue in his security clearance hearings, because of Tatlock's communist associations.[75] Throughout the development of the atomic bomb, Oppenheimer was under investigation by both the FBI and the Manhattan Project's internal security arm for left-wing associations he was known to have had in the past. He was followed by Army security agents during a trip to California in June 1943 to visit Tatlock, who was suffering from depression. Oppenheimer spent the night in her apartment.[76] Tatlock committed suicide on January 4, 1944, leaving Oppenheimer deeply grieved.[77] Many of Oppenheimer's closest associates were active in the Communist Party in the 1930s or 1940s, including his brother Frank, Frank's wife Jackie,[78] Kitty,[79] Tatlock, his landlady Mary Ellen Washburn,[80] and several of his graduate students at Berkeley.[81] Mysticism Oppenheimer's diverse interests sometimes interrupted his focus on science. He liked things that were difficult, and since much of the scientific work appeared easy for him, he developed an interest in the mystical and the cryptic. He also had an interest in learning languages and learned Sanskrit,[note 3] under Arthur W. Ryder at Berkeley.[83] He eventually read the Hindu scriptures such as the Bhagavad Gita and the Upanishads in original Sanskrit and deeply pondered them. He later cited the Gita as one of the books that most shaped his philosophy of life.[84][85] His close confidant and colleague, Nobel Prize winner Isidor Rabi, later gave his own interpretation: Oppenheimer was overeducated in those fields, which lie outside the scientific tradition, such as his interest in religion, in the Hindu religion in particular, which resulted in a feeling of mystery of the universe that surrounded him like a fog. He saw physics clearly, looking toward what had already been done, but at the border he tended to feel there was much more of the mysterious and novel than there actually was ... [he turned] away from the hard, crude methods of theoretical physics into a mystical realm of broad intuition.[86] In spite of this, observers such as Nobel Prize-winning physicist Luis Alvarez have suggested that if he had lived long enough to see his predictions substantiated by experiment, Oppenheimer might have won a Nobel Prize for his work on gravitational collapse, concerning neutron stars and black holes.[87][88] In retrospect, some physicists and historians consider this his most important contribution, though it was not taken up by other scientists in his lifetime.[89] The physicist and historian Abraham Pais once asked Oppenheimer what he considered his most important scientific contributions; Oppenheimer cited his work on electrons and positrons, not his work on gravitational contraction.[90] Oppenheimer was nominated for the Nobel Prize for physics three times, in 1946, 1951 and 1967, but never won.[91][92] Manhattan Project Los Alamos Main article: Los Alamos Laboratory On October 9, 1941, two months before the United States entered World War II, President Franklin D. Roosevelt approved a crash program to develop an atomic bomb.[93] In May 1942, National Defense Research Committee Chairman James B. Conant, who had been one of Oppenheimer's lecturers at Harvard, invited Oppenheimer to take over work on fast neutron calculations, a task Oppenheimer threw himself into with full vigor. He was given the title "Coordinator of Rapid Rupture", which specifically referred to the propagation of a fast neutron chain reaction in an atomic bomb. One of his first acts was to host a summer school for bomb theory at his building in Berkeley. The mix of European physicists and his own students—a group including Robert Serber, Emil Konopinski, Felix Bloch, Hans Bethe and Edward Teller—kept themselves busy by calculating what needed to be done, and in what order, to make the bomb.[94] Men in suits and uniforms stand on a dais decorated with bunting and salute. Presentation of the Army-Navy "E" Award at Los Alamos on October 16, 1945. Oppenheimer (left) gave his farewell speech as director on this occasion. Robert Gordon Sproul right, in suit, accepted the award on behalf of the University of California from Leslie Groves (center).[95] In June 1942, the US Army established the Manhattan Project to handle its part in the atom bomb project and began the process of transferring responsibility from the Office of Scientific Research and Development to the military.[96] In September, Groves was appointed director of what became known as the Manhattan Project.[97] He selected Oppenheimer to head the project's secret weapons laboratory. This choice surprised many, because Oppenheimer had left-wing political views and no record as a leader of large projects. Groves was concerned by the fact that Oppenheimer did not have a Nobel Prize and might not have had the prestige to direct fellow scientists.[98] But he was impressed by Oppenheimer's singular grasp of the practical aspects of designing and constructing an atomic bomb and by the breadth of his knowledge. As a military engineer, Groves knew that this would be vital in an interdisciplinary project that would involve not just physics, but chemistry, metallurgy, ordnance and engineering. Groves also detected in Oppenheimer something that many others did not, an "overweening ambition" that Groves reckoned would supply the drive necessary to push the project to a successful conclusion. Isidor Rabi considered the appointment "a real stroke of genius on the part of General Groves, who was not generally considered to be a genius".[99] Oppenheimer and Groves decided that for security and cohesion they needed a centralized, secret research laboratory in a remote location. Scouting for a site in late 1942, Oppenheimer was drawn to New Mexico, not far from his ranch. On November 16, 1942, Oppenheimer, Groves and others toured a prospective site. Oppenheimer feared that the high cliffs surrounding the site would make his people feel claustrophobic, while the engineers were concerned with the possibility of flooding. He then suggested and championed a site that he knew well: a flat mesa near Santa Fe, New Mexico, which was the site of a private boys' school, the Los Alamos Ranch School. The engineers were concerned about the poor access road and the water supply but otherwise felt that it was ideal.[100] The Los Alamos Laboratory was built on the site of the school, taking over some of its buildings, while many new buildings were erected in great haste. At the laboratory, Oppenheimer assembled a group of the top physicists of the time, which he called the "luminaries".[101] Los Alamos was initially supposed to be a military laboratory, and Oppenheimer and other researchers were to be commissioned into the Army. He went so far as to order himself a lieutenant colonel's uniform and take the Army physical test, which he failed. Army doctors considered him underweight at 128 pounds (58 kg), diagnosed his chronic cough as tuberculosis, and were concerned about his chronic lumbosacral joint pain.[102] The plan to commission scientists fell through when Rabi and Robert Bacher balked at the idea. Conant, Groves, and Oppenheimer devised a compromise whereby the laboratory was operated by the University of California under contract to the War Department.[103] It soon turned out that Oppenheimer had hugely underestimated the magnitude of the project; Los Alamos grew from a few hundred people in 1943 to over 6,000 in 1945.[102] Oppenheimer at first had difficulty with the organizational division of large groups, but rapidly learned the art of large-scale administration after he took up permanent residence on the mesa. He was noted for his mastery of all scientific aspects of the project and for his efforts to control the inevitable cultural conflicts between scientists and the military. He was an iconic figure to his fellow scientists, as much a symbol of what they were working toward as a scientific director. Victor Weisskopf put it thus: Oppenheimer directed these studies, theoretical and experimental, in the real sense of the words. Here his uncanny speed in grasping the main points of any subject was a decisive factor; he could acquaint himself with the essential details of every part of the work. He did not direct from the head office. He was intellectually and physically present at each decisive step. He was present in the laboratory or in the seminar rooms, when a new effect was measured, when a new idea was conceived. It was not that he contributed so many ideas or suggestions; he did so sometimes, but his main influence came from something else. It was his continuous and intense presence, which produced a sense of direct participation in all of us; it created that unique atmosphere of enthusiasm and challenge that pervaded the place throughout its time.[104] At this point in the war, there was considerable anxiety among the scientists that the Germans might be making faster progress on an atomic weapon than they were.[105][106] In a letter dated May 25, 1943, Oppenheimer responded to a proposal by Fermi to use radioactive materials to poison German food supplies. Oppenheimer asked Fermi whether he could produce enough strontium without letting too many in on the secret. Oppenheimer continued, "I think we should not attempt a plan unless we can poison food sufficient to kill a half a million men."[107] A group of men in shirtsleeves sitting on folding chairs. A group of physicists at the 1946 Los Alamos colloquium on the Super. In the front row are Norris Bradbury, John Manley, Enrico Fermi and J.M.B. Kellogg. Behind Manley is Oppenheimer (wearing jacket and tie), and to his left is Richard Feynman. The army colonel on the far left is Oliver Haywood. In the third row between Haywood and Oppenheimer is Edward Teller. In 1943 development efforts were directed to a plutonium gun-type fission weapon called "Thin Man". Initial research on the properties of plutonium was done using cyclotron-generated plutonium-239, which was extremely pure but could be created only in tiny amounts. When Los Alamos received the first sample of plutonium from the X-10 Graphite Reactor in April 1944, a problem was discovered: reactor-bred plutonium had a higher concentration of plutonium-240, making it unsuitable for use in a gun-type weapon.[108] In July 1944, Oppenheimer abandoned the gun design in favor of an implosion-type weapon. Using chemical explosive lenses, a sub-critical sphere of fissile material could be squeezed into a smaller and denser form. The metal needed to travel only very short distances, so the critical mass would be assembled in much less time.[109] In August 1944, Oppenheimer implemented a sweeping reorganization of the Los Alamos laboratory to focus on implosion.[110] He concentrated the development efforts on the gun-type device, a simpler design that only had to work with uranium-235, in a single group; this device became Little Boy in February 1945.[111] After a mammoth research effort, the more complex design of the implosion device, known as the "Christy gadget" after Robert Christy, another student of Oppenheimer's,[112] was finalized in a meeting in Oppenheimer's office on February 28, 1945.[113] In May 1945 an Interim Committee was created to advise and report on wartime and postwar policies regarding the use of nuclear energy. The Interim Committee in turn established a scientific panel consisting of Arthur Compton, Fermi, Lawrence and Oppenheimer to advise it on scientific issues. In its presentation to the Interim Committee, the scientific panel offered its opinion not just on the likely physical effects of an atomic bomb, but on its likely military and political impact.[114] This included opinions on such sensitive issues as whether the Soviet Union should be advised of the weapon in advance of its use against Japan.[115] Trinity Main article: Trinity (nuclear test) The Trinity test of the Manhattan Project was the first detonation of a nuclear device.[116] The joint work of the scientists at Los Alamos resulted in the world's first nuclear explosion, near Alamogordo, New Mexico, on July 16, 1945. Oppenheimer had given the site the codename "Trinity" in mid-1944 and said later that it was from one of John Donne's Holy Sonnets. According to the historian Gregg Herken, this naming could have been an allusion to Jean Tatlock, who had committed suicide a few months before and had in the 1930s introduced Oppenheimer to Donne's work.[117] Oppenheimer later recalled that, while witnessing the explosion, he thought of a verse from the Bhagavad Gita (XI,12): divi sūryasahasrasya bhavedyugapadutthitā yadi bhāḥ sadṛṥī sā syādbhāsastasya mahātmanaḥ "If the radiance of a thousand suns were to burst at once into the sky, that would be like the splendor of the mighty one".[118] Years later he would explain that another verse had also entered his head at that time: namely, the famous verse "kālo'smi lokakṣayakṛtpravṛddho lokānsamāhartumiha pravṛttaḥ" (XI,32),[119] which he translated as "I am become Death, the destroyer of worlds."[note 2] In 1965, when he was persuaded to quote again for a television broadcast, he said: We knew the world would not be the same. A few people laughed, a few people cried. Most people were silent. I remembered the line from the Hindu scripture, the Bhagavad Gita; Vishnu is trying to persuade the Prince that he should do his duty and, to impress him, takes on his multi-armed form and says, "Now I am become Death, the destroyer of worlds." I suppose we all thought that, one way or another.[120] Among those present with Oppenheimer in the control bunker at the site were his brother Frank and Brigadier General Thomas Farrell. When Jeremy Bernstein asked Frank what Robert's first words after the test had been, the answer was "I guess it worked."[123] Farrell summarized Robert's reaction as follows: Dr. Oppenheimer, on whom had rested a very heavy burden, grew tenser as the last seconds ticked off. He scarcely breathed. He held on to a post to steady himself. For the last few seconds, he stared directly ahead and then when the announcer shouted "Now!" and there came this tremendous burst of light followed shortly thereafter by the deep growling roar of the explosion, his face relaxed into an expression of tremendous relief.[124] Rabi noticed Oppenheimer's disconcerting triumphalism: "I'll never forget his walk; I'll never forget the way he stepped out of the car ... his walk was like High Noon ... this kind of strut. He had done it."[125] At an assembly at Los Alamos on August 6 (the evening of the atomic bombing of Hiroshima), Oppenheimer took to the stage and clasped his hands together "like a prize-winning boxer" while the crowd cheered. He noted his regret the weapon had not been available in time to use against Nazi Germany.[126] But he and many of the project staff were very upset about the bombing of Nagasaki, as they did not feel the second bomb was necessary from a military point of view.[127] He traveled to Washington on August 17 to hand-deliver a letter to Secretary of War Henry L. Stimson expressing his revulsion and his wish to see nuclear weapons banned.[128] In October 1945, Oppenheimer was granted an interview with President Harry S. Truman. The meeting went badly after Oppenheimer said he felt he had "blood on my hands". The remark infuriated Truman and put an end to the meeting. Truman later told his Undersecretary of State Dean Acheson, "I don't want to see that son-of-a-bitch in this office ever again."[129][130] For his services as director of Los Alamos, Oppenheimer was awarded the Medal for Merit by President Truman in 1946.[131] Postwar activities Oppenheimer's Van Gogh, Enclosed Field with Rising Sun (1889).[132] The Manhattan Project was top secret and did not become public knowledge until after the bombings of Hiroshima and Nagasaki, and Oppenheimer became a national spokesman for science who was emblematic of a new type of technocratic power.[77] He became a household name and his portrait appeared on the covers of Life and Time.[133][134] Nuclear physics became a powerful force as all governments of the world began to realize the strategic and political power that came with nuclear weapons. Like many scientists of his generation, he felt that security from atomic bombs would come only from a transnational organization such as the newly formed United Nations, which could institute a program to stifle a nuclear arms race.[135] Institute for Advanced Study In November 1945, Oppenheimer left Los Alamos to return to Caltech,[136] but soon found that his heart was no longer in teaching.[137] In 1947, he accepted an offer from Lewis Strauss to take up the directorship of the Institute for Advanced Study in Princeton, New Jersey. This meant moving back east and leaving Ruth Tolman, the wife of his friend Richard Tolman, with whom he had begun an affair after leaving Los Alamos.[138] The job came with a salary of $20,000 per annum, plus rent-free accommodation in the director's house, a 17th-century manor with a cook and groundskeeper, surrounded by 265 acres (107 ha) of woodlands.[139] He collected European furniture, and French post-impressionist and Fauvist artworks. His art collection included works by Cézanne, Derain, Despiau, de Vlaminck, Picasso, Rembrandt, Renoir, Van Gogh and Vuillard.[140] Four storey red brick building with a white clock tower. Institute for Advanced Study in Princeton, New Jersey Oppenheimer brought together intellectuals at the height of their powers and from a variety of disciplines to answer the most pertinent questions of the age. He directed and encouraged the research of many well-known scientists, including Freeman Dyson, and the duo of Chen Ning Yang and Tsung-Dao Lee, who won a Nobel Prize for their discovery of parity non-conservation. He also instituted temporary memberships for scholars from the humanities, such as T. S. Eliot and George F. Kennan. Some of these activities were resented by a few members of the mathematics faculty, who wanted the institute to stay a bastion of pure scientific research. Abraham Pais said that Oppenheimer himself thought that one of his failures at the institute was being unable to bring together scholars from the natural sciences and the humanities.[141] During a series of conferences in New York from 1947 through 1949, physicists switched back from war work to theoretical issues. Under Oppenheimer's direction, physicists tackled the greatest outstanding problem of the pre-war years: infinite, divergent, and nonsensical expressions in the quantum electrodynamics of elementary particles. Julian Schwinger, Richard Feynman and Shin'ichiro Tomonaga tackled the problem of regularization, and developed techniques that became known as renormalization. Freeman Dyson was able to prove that their procedures gave similar results. The problem of meson absorption and Hideki Yukawa's theory of mesons as the carrier particles of the strong nuclear force were also tackled. Probing questions from Oppenheimer prompted Robert Marshak's innovative two-meson hypothesis: that there are actually two types of mesons, pions and muons. This led to Cecil Frank Powell's breakthrough and subsequent Nobel Prize for the discovery of the pion.[142][note 4] Atomic Energy Commission A man in a suit seated, smoking a cigarette. Oppenheimer in 1946 with his trademark cigarette As a member of the Board of Consultants to a committee appointed by Truman, Oppenheimer strongly influenced the Acheson–Lilienthal Report. In this report, the committee advocated the creation of an international Atomic Development Authority, which would own all fissionable material and the means of its production, such as mines and laboratories, and atomic power plants where it could be used for peaceful energy production. Bernard Baruch was appointed to translate this report into a proposal to the United Nations, resulting in the Baruch Plan of 1946. The Baruch Plan introduced many additional provisions regarding enforcement, in particular requiring inspection of the Soviet Union's uranium resources. It was seen as an attempt to maintain the United States' nuclear monopoly and rejected by the Soviets. With this, it became clear to Oppenheimer that an arms race was unavoidable, due to the mutual suspicion of the United States and the Soviet Union,[144] which even Oppenheimer was starting to distrust.[145] After the Atomic Energy Commission (AEC) came into being in 1947 as a civilian agency in control of nuclear research and weapons issues, Oppenheimer was appointed as the chairman of its General Advisory Committee (GAC). From this position he advised on a number of nuclear-related issues, including project funding, laboratory construction and even international policy—though the GAC's advice was not always heeded.[146] As chairman of the GAC, Oppenheimer lobbied vigorously for international arms control and funding for basic science, and attempted to influence policy away from a heated arms race.[147] The first atomic bomb test by the Soviet Union in August 1949 came earlier than Americans expected, and over the next several months there was an intense debate within the U.S. government, military, and scientific communities over whether to proceed with the development of the far more powerful, nuclear fusion-based hydrogen bomb, then known as "the Super".[148] Oppenheimer had been aware of the possibility of a thermonuclear weapon since the days of the Manhattan Project and had allocated a limited amount of theoretical research work toward the possibility at the time, but nothing more than that, given the pressing need to develop a fission weapon.[149] Immediately following the end of the war, Oppenheimer argued against continuing work on the Super at that time, due to both lack of need and the enormous human casualties that would result from its use.[150][151] Now in October 1949, Oppenheimer and the GAC recommended against the development of the Super.[152] He and the other GAC members were motivated partly by ethical concerns, feeling that such a weapon could only be strategically used, resulting in millions of deaths: "Its use therefore carries much further than the atomic bomb itself the policy of exterminating civilian populations."[153] They also had practical qualms, as there was no workable design for a hydrogen bomb at the time.[154] Regarding the possibility of the Soviet Union developing a thermonuclear weapon, the GAC felt that the United States could have an adequate stockpile of atomic weapons to retaliate against any thermonuclear attack.[155] In that connection, Oppenheimer and the others were concerned about the opportunity costs that would be incurred if nuclear reactors were diverted from materials needed for atom bomb production to the materials such as tritium needed for a thermonuclear weapon.[156][157] A majority of the AEC subsequently endorsed the GAC recommendation, and Oppenheimer thought that the fight against the Super would triumph, but proponents of the weapon lobbied the White House vigorously.[158] On January 31, 1950, Truman, who was predisposed to proceed with the development of the weapon anyway, made the formal decision to do so.[159] Oppenheimer and other GAC opponents of the project, especially James Conant, felt disheartened and considered resigning from the committee.[160] They stayed on, though their views on the hydrogen bomb were well known.[161] In 1951, Edward Teller and mathematician Stanislaw Ulam developed what became known as the Teller-Ulam design for a hydrogen bomb.[162] This new design seemed technically feasible and Oppenheimer officially acceded to the weapon's development,[163] while still looking for ways in which its testing or deployment or use could be questioned.[164] As he later recalled: The program we had in 1949 was a tortured thing that you could well argue did not make a great deal of technical sense. It was therefore possible to argue also that you did not want it even if you could have it. The program in 1951 was technically so sweet that you could not argue about that. The issues became purely the military, the political and the humane problem of what you were going to do about it once you had it.[165] Oppenheimer, Conant, and Lee DuBridge, another member who had opposed the H-bomb decision, left the GAC when their terms expired in August 1952.[166] Truman had declined to reappoint them, as he wanted new voices on the committee who were more in support of H-bomb development.[167] In addition, various opponents of Oppenheimer had communicated to Truman their desire that Oppenheimer leave the committee.[168] Panels and study groups Oppenheimer played a role on a number of government panels and study projects during the late 1940s and early 1950s, some of which found him in the middle of controversies and power struggles.[169] In 1948 Oppenheimer chaired the Department of Defense's Long-Range Objectives Panel, which looked at the military utility of nuclear weapons including how they might be delivered.[170] After a year's worth of study, in spring 1952 Oppenheimer wrote the draft report of Project GABRIEL, which examined the dangers of nuclear fallout.[171] Oppenheimer was also a member of the Science Advisory Committee of the Office of Defense Mobilization.[172] Oppenheimer participated in Project Charles during 1951, which examined the possibility of creating an effective air defense of the United States against atomic attack, and in the follow-on Project East River in 1952, which, with Oppenheimer's input, recommended building a warning system that would provide one-hour notice to atomic attacks against American cities.[171] Those two projects led to Project Lincoln in 1952, a large effort where Oppenheimer was one of the senior scientists.[171] Undertaken at the MIT Lincoln Laboratory, which had recently been founded to study issues of air defense, this in turn led to the Lincoln Summer Study Group, where Oppenheimer became a key figure.[173] Oppenheimer's and other scientists' urging that resources be allocated to air defense in preference to large retaliatory strike capabilities brought an immediate response of objection from the United States Air Force (USAF),[174] and debate ensued about whether Oppenheimer and allied scientists, or the Air Force, was embracing an inflexible "Maginot Line" philosophy.[175] In any case, the Summer Study Group's work eventually led to the building of the Distant Early Warning Line.[176] Teller, who had been so uninterested in work on the atomic bomb at Los Alamos during the war that Oppenheimer had given him time instead to work on his own project of the hydrogen bomb,[177] left Los Alamos in 1951 to help found, in 1952, a second laboratory at what would become the Lawrence Livermore National Laboratory.[178] Oppenheimer had defended the history of work done at Los Alamos and opposed the creation of the second laboratory.[179] Project Vista looked at improving U.S. tactical warfare capabilities.[171] Oppenheimer was a late addition to the project in 1951, but wrote a key chapter of the report that challenged the doctrine of strategic bombardment and advocated for smaller tactical nuclear weapons which would be more useful in a limited theater conflict against enemy forces.[180] Strategic thermonuclear weapons delivered by long-range jet bombers would necessarily be under the control of the U.S. Air Force, whereas the Vista conclusions recommended an increased role for the U.S. Army and U.S. Navy as well.[181] The Air Force reaction to this was immediately hostile,[182] and it succeeded in getting the Vista report suppressed.[183] During 1952 Oppenheimer chaired the five-member State Department Panel of Consultants on Disarmament,[184] which first urged that the United States postpone its planned first test of the hydrogen bomb and seek a thermonuclear test ban with the Soviet Union, on the grounds that avoiding a test might forestall the development of a catastrophic new weapon and open the way for new arms agreements between the two nations.[185] But the panel lacked political allies in Washington, and the Ivy Mike shot went ahead as scheduled.[184] The panel then issued a final report in January 1953, which, influenced by many of Oppenheimer's deeply felt beliefs, presented a pessimistic vision of the future in which neither the United States nor the Soviet Union could establish effective nuclear superiority but both sides could effect terrible damage on the other.[186] One of the panel's recommendations, which Oppenheimer felt was especially important,[187] was that the U.S. government practice less secrecy and more openness toward the American people about the realities of the nuclear balance and the dangers of nuclear warfare.[186] This notion found a receptive audience in the new Eisenhower administration and led to creation of Operation Candor.[188] Oppenheimer subsequently presented his view on the lack of utility of ever-larger nuclear arsenals to the American public in a June 1953 article in Foreign Affairs,[189] and it received attention in major American newspapers.[190] Thus by 1953, Oppenheimer had reached another peak of influence, being involved in multiple different government posts and projects and having access to crucial strategic plans and force levels.[90] But at the same time, he had become the enemy of the proponents of strategic bombardment, who viewed his opposition to the H-bomb, followed by these accumulated positions and stances, with a combination of bitterness and distrust.[191] This view was paired with their fear that Oppenheimer's fame and powers of persuasion had made him dangerously influential in government, military, and scientific circles.[192] Security hearing Main article: Oppenheimer security hearing The FBI under J. Edgar Hoover had been following Oppenheimer since before the war, when he showed communist sympathies as a professor at Berkeley and had been close to members of the Communist Party, including his wife and brother. They strongly suspected that he himself was a member of the party, based on wiretaps in which party members referred to him or appeared to refer to him as a communist, as well as reports from informers within the party.[193] He had been under close surveillance since the early 1940s, his home and office bugged, his phone tapped and his mail opened.[194] The FBI furnished Oppenheimer's political enemies with evidence that implicated communist ties. These enemies included Strauss, an AEC commissioner who had long harbored resentment against Oppenheimer both for his activity in opposing the hydrogen bomb and for his humiliation of Strauss before Congress some years earlier; regarding Strauss's opposition to the export of radioactive isotopes to other nations, Oppenheimer had memorably categorized these as "less important than electronic devices but more important than, let us say, vitamins".[195] Two men in suits at a table covered in papers. There is an American flag in the background. President Dwight D. Eisenhower receives a report from Lewis L. Strauss, Chairman of the Atomic Energy Commission, on the Operation Castle hydrogen bomb tests in the Pacific, March 30, 1954. Strauss pressed for Oppenheimer's security clearance to be revoked. On June 7, 1949, Oppenheimer testified before the House Un-American Activities Committee that he had associations with the Communist Party USA in the 1930s.[196] He testified that some of his students, including David Bohm, Giovanni Rossi Lomanitz, Philip Morrison, Bernard Peters, and Joseph Weinberg had been communists at the time they had worked with him at Berkeley. Frank Oppenheimer and his wife Jackie testified before HUAC that they had been members of the Communist Party USA. Frank was subsequently fired from his University of Minnesota position. Unable to find work in physics for many years, he became a cattle rancher in Colorado. He later taught high school physics and was the founder of the San Francisco Exploratorium.[81][197] The triggering event for the security hearing happened on November 7, 1953,[198] when William Liscum Borden, who until earlier in the year had been the executive director of the United States Congress Joint Committee on Atomic Energy, sent Hoover a letter saying that "more probably than not J. Robert Oppenheimer is an agent of the Soviet Union."[199] Eisenhower never exactly believed the allegations in the letter, but felt compelled to move forward with an investigation,[200] and on December 3 he ordered that a "blank wall" be placed between Oppenheimer and any government or military secrets.[201] On December 21, 1953, Strauss told Oppenheimer that his security clearance had been suspended, pending resolution of a series of charges outlined in a letter, and discussed his resigning by way of requesting termination of his consulting contract with the AEC.[202] Oppenheimer chose not to resign and requested a hearing instead.[203] The charges were outlined in a letter from Kenneth D. Nichols, General Manager of the AEC.[204][205] The hearing that followed in April–May 1954, which was held in secret, focused on Oppenheimer's past communist ties and his association during the Manhattan Project with suspected disloyal or communist scientists.[206] It then continued with an examination of Oppenheimer's opposition to the H-bomb and stances in subsequent projects and study groups.[207] A transcript of the hearings was published in June 1954,[208] with some redactions. The US Department of Energy made public the full text of the transcript in October 2014.[209][210] Head and shoulders of a man with bushy eyebrows. Oppenheimer's former colleague, physicist Edward Teller, testified on behalf of the government at Oppenheimer's security hearing in 1954.[211] One of the key elements in this hearing was Oppenheimer's earliest testimony about George Eltenton's approach to various Los Alamos scientists, a story that Oppenheimer confessed he had fabricated to protect his friend Haakon Chevalier. Unknown to Oppenheimer, both versions were recorded during his interrogations of a decade before. He was surprised on the witness stand with transcripts of these, which he had not been given a chance to review. In fact, Oppenheimer had never told Chevalier that he had finally named him, and the testimony had cost Chevalier his job. Both Chevalier and Eltenton confirmed mentioning that they had a way to get information to the Soviets, Eltenton admitting he said this to Chevalier and Chevalier admitting he mentioned it to Oppenheimer, but both put the matter in terms of gossip and denied any thought or suggestion of treason or thoughts of espionage, either in planning or in deed. Neither was ever convicted of any crime.[212] Teller testified that he considered Oppenheimer loyal to the US government, but that: In a great number of cases, I have seen Dr. Oppenheimer act—I understand that Dr. Oppenheimer acted—in a way which was for me was exceedingly hard to understand. I thoroughly disagreed with him in numerous issues and his actions frankly appeared to me confused and complicated. To this extent I feel that I would like to see the vital interests of this country in hands which I understand better, and therefore trust more. In this very limited sense I would like to express a feeling that I would feel personally more secure if public matters would rest in other hands.[213] This led to outrage by the scientific community and Teller's virtual expulsion from academic science.[214] Ernest Lawrence refused to testify on the grounds that he was suffering from an attack of ulcerative colitis, but an interview transcript in which he condemned Oppenheimer was presented as evidence in his absence.[215] Groves, threatened by the FBI as having been potentially part of a coverup about the Chevalier contact in 1943, likewise testified against Oppenheimer.[216] Many top scientists, as well as government and military figures, testified on Oppenheimer's behalf. Inconsistencies in his testimony and his erratic behavior on the stand, at one point saying he had given a "cock and bull story" and that this was because he "was an idiot", convinced some that he was unstable, unreliable and a possible security risk. Oppenheimer's clearance was revoked one day before it was due to lapse anyway.[217] Rabi commented that Oppenheimer was merely a government consultant at the time anyway and that if the government "didn't want to consult the guy, then don't consult him".[218] During his hearing, Oppenheimer testified willingly on the left-wing activities of many of his scientific colleagues. Had Oppenheimer's clearance not been stripped, he might have been remembered as someone who had "named names" to save his own reputation.[219] As it happened, Oppenheimer was seen by most of the scientific community as a martyr to McCarthyism, an eclectic liberal who was unjustly attacked by warmongering enemies, symbolic of the shift of scientific creativity from academia into the military.[220] Wernher von Braun summed up his opinion about the matter with a quip to a Congressional committee: "In England, Oppenheimer would have been knighted."[221] In a seminar at The Wilson Center in 2009, based on an extensive analysis of the Vassiliev notebooks taken from the KGB archives, John Earl Haynes, Harvey Klehr and Alexander Vassiliev confirmed that Oppenheimer never was involved in espionage for the Soviet Union. Soviet intelligence tried repeatedly to recruit him, but was never successful; Oppenheimer did not spy on the United States. In addition, he had several persons removed from the Manhattan Project who had sympathies to the Soviet Union.[222] Haynes, Klehr and Vassiliev also state Oppenheimer "was, in fact, a concealed member of the CPUSA in the late 1930s".[223] According to biographer Ray Monk: "He was, in a very practical and real sense, a supporter of the Communist Party. Moreover, in terms of the time, effort and money spent on party activities, he was a very committed supporter".[224] On December 16, 2022, United States Secretary of Energy Jennifer Granholm vacated the 1954 revocation of Oppenheimer's security clearance.[4] Her statement said, "In 1954, the Atomic Energy Commission revoked Dr. Oppenheimer’s security clearance through a flawed process that violated the Commission’s own regulations. As time has passed, more evidence has come to light of the bias and unfairness of the process that Dr. Oppenheimer was subjected to while the evidence of his loyalty and love of country have only been further affirmed."[225] Final years and death The frontiers of science are separated now by long years of study, by specialized vocabularies, arts, techniques, and knowledge from the common heritage even of a most civilized society; and anyone working at the frontier of such science is in that sense a very long way from home, a long way too from the practical arts that were its matrix and origin, as indeed they were of what we today call art. Robert Oppenheimer, "Prospects in the Arts and Sciences" in Man's Right to Knowledge[226] Starting in 1954, Oppenheimer lived for several months of the year on the island of Saint John in the U.S. Virgin Islands. In 1957, he purchased a 2-acre (0.81 ha) tract of land on Gibney Beach, where he built a spartan home on the beach.[227] He spent a considerable amount of time sailing with his daughter Toni and wife Kitty.[228] Oppenheimer's first public appearance following the stripping of his security clearance was a lecture titled "Prospects in the Arts and Sciences" for the Columbia University Bicentennial radio show Man's Right to Knowledge, in which he outlined his philosophy and his thoughts on the role of science in the modern world.[229][230] He had been selected for the final episode of the lecture series two years prior to the security hearing, though the university remained adamant that he stay on even after the controversy.[231] In February 1955, the president of the University of Washington, Henry Schmitz, abruptly canceled an invitation to Oppenheimer to deliver a series of lectures there. Schmitz's decision caused an uproar among the students; 1,200 of them signed a petition protesting the decision, and Schmitz was burned in effigy. While they marched in protest, the state of Washington outlawed the Communist Party, and required all government employees to swear a loyalty oath. Edwin Albrecht Uehling, the chairman of the physics department and a colleague of Oppenheimer's from Berkeley, appealed to the university senate, and Schmitz's decision was overturned by a vote of 56 to 40. Oppenheimer stopped briefly in Seattle to change planes on a trip to Oregon, and was joined for coffee during his layover by several University of Washington faculty, but Oppenheimer never lectured there.[232][233] A group of men in uniforms, suits and academic dress sit for a formal group photograph Award of honorary degrees at Harvard to Oppenheimer (left), George C. Marshall (third from left) and Omar N. Bradley (fifth from left). The President of Harvard University, James B. Conant, sits between Marshall and Bradley. June 5, 1947 Oppenheimer was increasingly concerned about the potential danger that scientific inventions could pose to humanity. He joined with Albert Einstein, Bertrand Russell, Joseph Rotblat and other eminent scientists and academics to establish what would eventually, in 1960, become the World Academy of Art and Science. Significantly, after his public humiliation, he did not sign the major open protests against nuclear weapons of the 1950s, including the Russell–Einstein Manifesto of 1955, nor, though invited, did he attend the first Pugwash Conferences on Science and World Affairs in 1957.[234] In his speeches and public writings, Oppenheimer continually stressed the difficulty of managing the power of knowledge in a world in which the freedom of science to exchange ideas was more and more hobbled by political concerns. Oppenheimer delivered the Reith Lectures on the BBC in 1953, which were subsequently published as Science and the Common Understanding.[235] In 1955, Oppenheimer published The Open Mind, a collection of eight lectures that he had given since 1946 on the subject of nuclear weapons and popular culture. Oppenheimer rejected the idea of nuclear gunboat diplomacy. "The purposes of this country in the field of foreign policy", he wrote, "cannot in any real or enduring way be achieved by coercion". In 1957 the philosophy and psychology departments at Harvard invited Oppenheimer to deliver the William James Lectures. An influential group of Harvard alumni led by Edwin Ginn that included Archibald Roosevelt protested against the decision.[236] Some 1,200 people packed Sanders Theatre to hear Oppenheimer's six lectures, titled "The Hope of Order".[234] Oppenheimer delivered the Whidden Lectures at McMaster University in 1962, and these were published in 1964 as The Flying Trapeze: Three Crises for Physicists.[237] A tropical beach with sand, surf and trees. Some bathers enjoy the blue waters. Oppenheimer Beach, in Saint John, U.S. Virgin Islands Deprived of political power, Oppenheimer continued to lecture, write and work on physics. He toured Europe and Japan, giving talks about the history of science, the role of science in society, and the nature of the universe.[238] In September 1957, France made him an Officer of the Legion of Honor,[239] and on May 3, 1962, he was elected a Foreign Member of the Royal Society in Britain.[240][241] At the urging of many of Oppenheimer's political friends who had ascended to power, President John F. Kennedy awarded Oppenheimer the Enrico Fermi Award in 1963 as a gesture of political rehabilitation. Teller, the winner of the previous year's award, had also recommended Oppenheimer receive it, in the hope that it would heal the rift between them.[242] A little over a week after Kennedy's assassination, his successor, President Lyndon Johnson, presented Oppenheimer with the award, "for contributions to theoretical physics as a teacher and originator of ideas, and for leadership of the Los Alamos Laboratory and the atomic energy program during critical years".[243] Oppenheimer told Johnson: "I think it is just possible, Mr. President, that it has taken some charity and some courage for you to make this award today."[244] The rehabilitation implied by the award was partly symbolic, as Oppenheimer still lacked a security clearance and could have no effect on official policy, but the award came with a $50,000 tax-free stipend, and its award outraged many prominent Republicans in Congress. The late President Kennedy's widow Jacqueline, still living in the White House, made it a point to meet with Oppenheimer to tell him how much her husband had wanted him to have the medal.[245] While still a senator in 1959, Kennedy had been instrumental in voting to narrowly deny Oppenheimer's enemy Lewis Strauss a coveted government position as Secretary of Commerce, effectively ending Strauss's political career. This was partly due to lobbying by the scientific community on behalf of Oppenheimer.[246] Oppenheimer giving a speech during a 1966 visit to Israel Oppenheimer giving a speech during a 1966 visit to Israel Oppenheimer was a chain smoker who was diagnosed with throat cancer in late 1965. After inconclusive surgery, he underwent unsuccessful radiation treatment and chemotherapy late in 1966.[247] He fell into a coma on February 15, 1967, and died at his home in Princeton, New Jersey, on February 18, aged 62. A memorial service was held a week later at Alexander Hall on the campus of Princeton University. The service was attended by 600 of his scientific, political and military associates that included Bethe, Groves, Kennan, Lilienthal, Rabi, Smyth and Wigner. His brother Frank and the rest of his family were also there, as was the historian Arthur M. Schlesinger, Jr., the novelist John O'Hara, and George Balanchine, the director of the New York City Ballet. Bethe, Kennan and Smyth gave brief eulogies.[248] Oppenheimer's body was cremated and his ashes placed in an urn. His wife took the ashes to St. John and dropped the urn into the sea, within sight of the beach house.[249] In October 1972, Kitty died aged 62 from an intestinal infection complicated by a pulmonary embolism. Oppenheimer's ranch in New Mexico was then inherited by their son Peter, and the beach property was inherited by their daughter Katherine "Toni" Oppenheimer Silber. Toni was refused security clearance for her chosen vocation as a United Nations translator after the FBI brought up the old charges against her father. In January 1977 (three months after the end of her second marriage), she committed suicide aged 32; her ex-husband found her hanging from a beam in her family beach house.[250] She left the property to "the people of St. John for a public park and recreation area".[251] The original house was built too close to the coast and succumbed to a hurricane. Today the Virgin Islands Government maintains a Community Center in the area.[252] Legacy When Oppenheimer was stripped of his position of political influence in 1954, he symbolized for many the folly of scientists who believed they could control the use of their research, and the dilemmas of moral responsibility presented by science in the nuclear age.[253] The hearings were motivated by politics and personal enmities, and also reflected a stark divide in the nuclear weapons community.[254] One group viewed with passionate fear the Soviet Union as a mortal enemy and believed having the most powerful weaponry capable of providing the most massive retaliation was the best strategy for combating that threat. The other group felt that developing the H-bomb would not in fact improve the security position and that using the weapon against large civilian populations would be an act of genocide, and advocated instead a more flexible response to the Soviets involving tactical nuclear weapons, strengthened conventional forces, and arms control agreements. The first of these groups was the more powerful in political terms, and Oppenheimer became its target.[255][256] Rather than consistently oppose the "Red-baiting" of the late 1940s and early 1950s, Oppenheimer testified against some of his former colleagues and students, both before and during his hearing. In one incident, his damning testimony against former student Bernard Peters was selectively leaked to the press. Historians have interpreted this as an attempt by Oppenheimer to please his colleagues in the government and perhaps to divert attention from his own previous left-wing ties and those of his brother. In the end, it became a liability when it became clear that if Oppenheimer had really doubted Peters' loyalty, his recommending him for the Manhattan Project was reckless, or at least contradictory.[257] A man smiling in a suit in suit and one in a uniform chat around a pile of twisted metal. Oppenheimer and Leslie Groves in September 1945 at the remains of the Trinity test in New Mexico. The white canvas overshoes prevented fallout from sticking to the soles of their shoes.[258] Popular depictions of Oppenheimer view his security struggles as a confrontation between right-wing militarists (symbolized by Teller) and left-wing intellectuals (symbolized by Oppenheimer) over the moral question of weapons of mass destruction.[259] The Oppenheimer story has often been viewed by biographers and historians as a modern tragedy.[260][261][262] National security advisor and academic McGeorge Bundy, who had worked with Oppenheimer on the State Department Panel of Consultants, has written: "Quite aside from Oppenheimer's extraordinary rise and fall in prestige and power, his character has fully tragic dimensions in its combination of charm and arrogance, intelligence and blindness, awareness and insensitivity, and perhaps above all daring and fatalism. All these, in different ways, were turned against him in the hearings."[262] The question of the scientists' responsibility toward humanity inspired Bertolt Brecht's drama Galileo (1955), left its imprint on Friedrich Dürrenmatt's Die Physiker, and is the basis of the opera Doctor Atomic by John Adams (2005), which was commissioned to portray Oppenheimer as a modern-day Faust. Heinar Kipphardt's play In the Matter of J. Robert Oppenheimer, after appearing on West German television, had its theatrical release in Berlin and Munich in October 1964. Oppenheimer's objections resulted in an exchange of correspondence with Kipphardt, in which the playwright offered to make corrections but defended the play.[263] It premiered in New York in June 1968, with Joseph Wiseman in the Oppenheimer role. New York Times theater critic Clive Barnes called it an "angry play and a partisan play" that sided with Oppenheimer but portrayed the scientist as a "tragic fool and genius".[264] Oppenheimer had difficulty with this portrayal. After reading a transcript of Kipphardt's play soon after it began to be performed, Oppenheimer threatened to sue the playwright, decrying "improvisations which were contrary to history and to the nature of the people involved".[265] Later Oppenheimer told an interviewer: The whole damn thing [his security hearing] was a farce, and these people are trying to make a tragedy out of it. ... I had never said that I had regretted participating in a responsible way in the making of the bomb. I said that perhaps he [Kipphardt] had forgotten Guernica, Coventry, Hamburg, Dresden, Dachau, Warsaw, and Tokyo; but I had not, and that if he found it so difficult to understand, he should write a play about something else.[266] Oppenheimer is the subject of numerous biographies, including American Prometheus: The Triumph and Tragedy of J. Robert Oppenheimer (2005) by Kai Bird and Martin J. Sherwin which won the Pulitzer Prize for Biography or Autobiography for 2006.[267] The 1980 BBC TV serial Oppenheimer, starring Sam Waterston, won three BAFTA Television Awards.[268][269] The Day After Trinity, a 1980 documentary about J. Robert Oppenheimer and the building of the atomic bomb, was nominated for an Academy Award and received a Peabody Award.[270][271] Oppenheimer's life has also been explored in the 2015 play Oppenheimer by Tom Morton-Smith,[272] and in the 1989 film Fat Man and Little Boy, where he was portrayed by Dwight Schultz.[273] In the upcoming American film Oppenheimer, directed by Christopher Nolan and based on American Prometheus, Oppenheimer is portrayed by actor Cillian Murphy.[274] A centennial conference and exhibit were held in 2004 at Berkeley,[275] with the proceedings of the conference published in 2005 as Reappraising Oppenheimer: Centennial Studies and Reflections.[276] His papers are in the Library of Congress.[277] As a scientist, Oppenheimer is remembered by his students and colleagues as being a brilliant researcher and engaging teacher who was the founder of modern theoretical physics in the United States. Because his scientific attentions often changed rapidly, he never worked long enough on any one topic and carried it to fruition to merit the Nobel Prize,[278] although his investigations contributing to the theory of black holes may have warranted the prize had he lived long enough to see them brought into fruition by later astrophysicists.[87] An asteroid, 67085 Oppenheimer, was named in his honor,[279] as was the lunar crater Oppenheimer.[280] As a military and public policy advisor, Oppenheimer was a technocratic leader in a shift in the interactions between science and the military and the emergence of "Big Science". During World War II, scientists became involved in military research to an unprecedented degree. Because of the threat fascism posed to civilization, they volunteered in great numbers both for technological and organizational assistance to the Allied effort, resulting in such powerful tools as radar, the proximity fuse and operations research. As a cultured, intellectual, theoretical physicist who became a disciplined military organizer, Oppenheimer represented the shift away from the idea that scientists had their "head in the clouds" and that knowledge on such previously esoteric subjects as the composition of the atomic nucleus had no "real-world" applications.[253] Two days before the Trinity test, Oppenheimer expressed his hopes and fears in a quotation from Bhartṛhari's Śatakatraya: In battle, in the forest, at the precipice in the mountains, On the dark great sea, in the midst of javelins and arrows, In sleep, in confusion, in the depths of shame, The good deeds a man has done before defend him.[281][282] Bibliography Oppenheimer, J. Robert (1954). Science and the Common Understanding. New York: Simon and Schuster. OCLC 34304713. Oppenheimer, J. Robert (1955). The Open Mind. New York: Simon and Schuster. OCLC 297109.} Oppenheimer, J. Robert (1964). The Flying Trapeze: Three Crises for Physicists. London: Oxford University Press. OCLC 592102.} Oppenheimer, J. Robert; Rabi, I.I (1969). Oppenheimer. New York: Scribner. OCLC 2729.} (posthumous) Oppenheimer, J. Robert; Smith, Alice Kimball; Weiner, Charles (1980). Robert Oppenheimer, Letters and Recollections. Cambridge, Massachusetts: Harvard University Press. ISBN 978-0-674-77605-0. OCLC 5946652. (posthumous) Oppenheimer, J. Robert; Metropolis, N.; Rota, Gian-Carlo; Sharp, D. H. (1984). Uncommon Sense. Cambridge, Massachusetts: Birkhäuser Boston. ISBN 978-0-8176-3165-9. OCLC 10458715. (posthumous) Oppenheimer, J. Robert (1989). Atom and Void: Essays on Science and Community. Princeton, New Jersey: Princeton University Press. ISBN 978-0-691-08547-0. OCLC 19981106. (posthumous) Notes  The meaning of the 'J' in J. Robert Oppenheimer has been a source of confusion. Historians Alice Kimball Smith and Charles Weiner sum up the general historical opinion in their volume Robert Oppenheimer: Letters and recollections, on page 1: "Whether the 'J' in Robert's name stood for Julius or, as Robert himself once said, 'for nothing' may never be fully resolved. His brother Frank surmised that the 'J' was symbolic, a gesture in the direction of naming the eldest son after the father but at the same time a signal that his parents did not want Robert to be a 'junior.'" In Peter Goodchild's J. Robert Oppenheimer: Shatterer of Worlds, it is said that Robert's father, Julius, added the empty initial to give Robert's name additional distinction, but Goodchild's book has no footnotes, so the source of this assertion is unclear. Robert's claim that the 'J' stood "for nothing" is taken from an interview conducted by Thomas S. Kuhn on November 18, 1963, which currently resides in the Archive for the History of Quantum Physics. On the other hand, Oppenheimer's birth certificate reads "Julius Robert Oppenheimer".  Oppenheimer spoke these words in the television documentary The Decision to Drop the Bomb (1965).[120] Oppenheimer read the original text in Sanskrit, and the translation is his own.[2] In the literature, the quote usually appears in the form "shatterer of worlds", because this was the form in which it first appeared in print, in Time magazine on November 8, 1948.[26] It later appeared in Robert Jungk's Brighter than a Thousand Suns: A Personal History of the Atomic Scientists (1958),[121] which was based on an interview with Oppenheimer.[122]  He also spoke Dutch, German, French and some Chinese.[82]  Due to the subsequent development of the Standard Model, the muon is now considered to be a lepton and not a meson.[143] Theoretical physics is a branch of physics that employs mathematical models and abstractions of physical objects and systems to rationalize, explain and predict natural phenomena. This is in contrast to experimental physics, which uses experimental tools to probe these phenomena. The advancement of science generally depends on the interplay between experimental studies and theory. In some cases, theoretical physics adheres to standards of mathematical rigour while giving little weight to experiments and observations.[a] For example, while developing special relativity, Albert Einstein was concerned with the Lorentz transformation which left Maxwell's equations invariant, but was apparently uninterested in the Michelson–Morley experiment on Earth's drift through a luminiferous aether.[1] Conversely, Einstein was awarded the Nobel Prize for explaining the photoelectric effect, previously an experimental result lacking a theoretical formulation.[2] Overview A physical theory is a model of physical events. It is judged by the extent to which its predictions agree with empirical observations. The quality of a physical theory is also judged on its ability to make new predictions which can be verified by new observations. A physical theory differs from a mathematical theorem in that while both are based on some form of axioms, judgment of mathematical applicability is not based on agreement with any experimental results.[3][4] A physical theory similarly differs from a mathematical theory, in the sense that the word "theory" has a different meaning in mathematical terms.[b] R i c =     {\displaystyle \mathrm {Ric} =kg} The equations for an Einstein manifold, used in general relativity to describe the curvature of spacetime A physical theory involves one or more relationships between various measurable quantities. Archimedes realized that a ship floats by displacing its mass of water, Pythagoras understood the relation between the length of a vibrating string and the musical tone it produces.[5][6] Other examples include entropy as a measure of the uncertainty regarding the positions and motions of unseen particles and the quantum mechanical idea that (action and) energy are not continuously variable. Theoretical physics consists of several different approaches. In this regard, theoretical particle physics forms a good example. For instance: "phenomenologists" might employ (semi-) empirical formulas and heuristics to agree with experimental results, often without deep physical understanding.[c] "Modelers" (also called "model-builders") often appear much like phenomenologists, but try to model speculative theories that have certain desirable features (rather than on experimental data), or apply the techniques of mathematical modeling to physics problems.[d] Some attempt to create approximate theories, called effective theories, because fully developed theories may be regarded as unsolvable or too complicated. Other theorists may try to unify, formalise, reinterpret or generalise extant theories, or create completely new ones altogether.[e] Sometimes the vision provided by pure mathematical systems can provide clues to how a physical system might be modeled;[f] e.g., the notion, due to Riemann and others, that space itself might be curved. Theoretical problems that need computational investigation are often the concern of computational physics. Theoretical advances may consist in setting aside old, incorrect paradigms (e.g., aether theory of light propagation, caloric theory of heat, burning consisting of evolving phlogiston, or astronomical bodies revolving around the Earth) or may be an alternative model that provides answers that are more accurate or that can be more widely applied. In the latter case, a correspondence principle will be required to recover the previously known result.[7][8] Sometimes though, advances may proceed along different paths. For example, an essentially correct theory may need some conceptual or factual revisions; atomic theory, first postulated millennia ago (by several thinkers in Greece and India) and the two-fluid theory of electricity[9] are two cases in this point. However, an exception to all the above is the wave–particle duality, a theory combining aspects of different, opposing models via the Bohr complementarity principle. Relationship between mathematics and physics Physical theories become accepted if they are able to make correct predictions and no (or few) incorrect ones. The theory should have, at least as a secondary objective, a certain economy and elegance (compare to mathematical beauty), a notion sometimes called "Occam's razor" after the 13th-century English philosopher William of Occam (or Ockham), in which the simpler of two theories that describe the same matter just as adequately is preferred (but conceptual simplicity may mean mathematical complexity).[10] They are also more likely to be accepted if they connect a wide range of phenomena. Testing the consequences of a theory is part of the scientific method. Physical theories can be grouped into three categories: mainstream theories, proposed theories and fringe theories. History Further information: History of physics Theoretical physics began at least 2,300 years ago, under the Pre-socratic philosophy, and continued by Plato and Aristotle, whose views held sway for a millennium. During the rise of medieval universities, the only acknowledged intellectual disciplines were the seven liberal arts of the Trivium like grammar, logic, and rhetoric and of the Quadrivium like arithmetic, geometry, music and astronomy. During the Middle Ages and Renaissance, the concept of experimental science, the counterpoint to theory, began with scholars such as Ibn al-Haytham and Francis Bacon. As the Scientific Revolution gathered pace, the concepts of matter, energy, space, time and causality slowly began to acquire the form we know today, and other sciences spun off from the rubric of natural philosophy. Thus began the modern era of theory with the Copernican paradigm shift in astronomy, soon followed by Johannes Kepler's expressions for planetary orbits, which summarized the meticulous observations of Tycho Brahe; the works of these men (alongside Galileo's) can perhaps be considered to constitute the Scientific Revolution. The great push toward the modern concept of explanation started with Galileo, one of the few physicists who was both a consummate theoretician and a great experimentalist. The analytic geometry and mechanics of Descartes were incorporated into the calculus and mechanics of Isaac Newton, another theoretician/experimentalist of the highest order, writing Principia Mathematica.[11] In it contained a grand synthesis of the work of Copernicus, Galileo and Kepler; as well as Newton's theories of mechanics and gravitation, which held sway as worldviews until the early 20th century. Simultaneously, progress was also made in optics (in particular colour theory and the ancient science of geometrical optics), courtesy of Newton, Descartes and the Dutchmen Snell and Huygens. In the 18th and 19th centuries Joseph-Louis Lagrange, Leonhard Euler and William Rowan Hamilton would extend the theory of classical mechanics considerably.[12] They picked up the interactive intertwining of mathematics and physics begun two millennia earlier by Pythagoras. Among the great conceptual achievements of the 19th and 20th centuries were the consolidation of the idea of energy (as well as its global conservation) by the inclusion of heat, electricity and magnetism, and then light. The laws of thermodynamics, and most importantly the introduction of the singular concept of entropy began to provide a macroscopic explanation for the properties of matter. Statistical mechanics (followed by statistical physics and Quantum statistical mechanics) emerged as an offshoot of thermodynamics late in the 19th century. Another important event in the 19th century was the discovery of electromagnetic theory, unifying the previously separate phenomena of electricity, magnetism and light. The pillars of modern physics, and perhaps the most revolutionary theories in the history of physics, have been relativity theory and quantum mechanics. Newtonian mechanics was subsumed under special relativity and Newton's gravity was given a kinematic explanation by general relativity. Quantum mechanics led to an understanding of blackbody radiation (which indeed, was an original motivation for the theory) and of anomalies in the specific heats of solids — and finally to an understanding of the internal structures of atoms and molecules. Quantum mechanics soon gave way to the formulation of quantum field theory (QFT), begun in the late 1920s. In the aftermath of World War 2, more progress brought much renewed interest in QFT, which had since the early efforts, stagnated. The same period also saw fresh attacks on the problems of superconductivity and phase transitions, as well as the first applications of QFT in the area of theoretical condensed matter. The 1960s and 70s saw the formulation of the Standard model of particle physics using QFT and progress in condensed matter physics (theoretical foundations of superconductivity and critical phenomena, among others), in parallel to the applications of relativity to problems in astronomy and cosmology respectively. All of these achievements depended on the theoretical physics as a moving force both to suggest experiments and to consolidate results — often by ingenious application of existing mathematics, or, as in the case of Descartes and Newton (with Leibniz), by inventing new mathematics. Fourier's studies of heat conduction led to a new branch of mathematics: infinite, orthogonal series.[13] Modern theoretical physics attempts to unify theories and explain phenomena in further attempts to understand the Universe, from the cosmological to the elementary particle scale. Where experimentation cannot be done, theoretical physics still tries to advance through the use of mathematical models. Mainstream theories Mainstream theories (sometimes referred to as central theories) are the body of knowledge of both factual and scientific views and possess a usual scientific quality of the tests of repeatability, consistency with existing well-established science and experimentation. There do exist mainstream theories that are generally accepted theories based solely upon their effects explaining a wide variety of data, although the detection, explanation, and possible composition are subjects of debate. Examples Analog models of gravity Big Bang Causality Chaos theory Classical field theory Classical mechanics Condensed matter physics (including solid state physics and the electronic structure of materials) Conservation law Conservation of angular momentum Conservation of energy Conservation of mass Conservation of momentum Continuum mechanics Cosmic censorship hypothesis Cosmological Constant CPT symmetry Dark matter Dynamics Dynamo theory Electromagnetism Electroweak interaction Field theory Fluctuation theorem Fluid dynamics Fluid mechanics Fundamental interaction General relativity Gravitational constant Heisenberg's uncertainty principle Kinetic theory of gases Laws of thermodynamics Maxwell's equations Newton's laws of motion Pauli exclusion principle Perturbation theory (quantum mechanics) Physical cosmology Planck constant Poincaré recurrence theorem Quantum biology Quantum chaos Quantum chromodynamics Quantum complexity theory Quantum computing Quantum dynamics Quantum electrochemistry Quantum electrodynamics Quantum field theory Quantum field theory in curved spacetime Quantum geometry Quantum information theory Quantum logic Quantum mechanics Quantum optics Quantum physics Quantum thermodynamics Relativistic quantum mechanics Scattering theory Solid mechanics Special relativity Spin–statistics theorem Spontaneous symmetry breaking Standard Model Statistical mechanics Statistical physics Theory of relativity Thermodynamics Wave–particle duality Weak interaction Proposed theories The proposed theories of physics are usually relatively new theories which deal with the study of physics which include scientific approaches, means for determining the validity of models and new types of reasoning used to arrive at the theory. However, some proposed theories include theories that have been around for decades and have eluded methods of discovery and testing. Proposed theories can include fringe theories in the process of becoming established (and, sometimes, gaining wider acceptance). Proposed theories usually have not been tested. In addition to the theories like those listed below, there are also different interpretations of quantum mechanics, which may or may not be considered different theories since it is debatable whether they yield different predictions for physical experiments, even in principle. For example, AdS/CFT correspondence, Chern–Simons theory, graviton, magnetic monopole, string theory, theory of everything. Fringe theories Fringe theories include any new area of scientific endeavor in the process of becoming established and some proposed theories. It can include speculative sciences. This includes physics fields and physical theories presented in accordance with known evidence, and a body of associated predictions have been made according to that theory. Some fringe theories go on to become a widely accepted part of physics. Other fringe theories end up being disproven. Some fringe theories are a form of protoscience and others are a form of pseudoscience. The falsification of the original theory sometimes leads to reformulation of the theory. Examples Aether (classical element) Luminiferous aether Digital physics Electrogravitics Stochastic electrodynamics Tesla's dynamic theory of gravity Thought experiments vs real experiments Main article: Thought experiment "Thought" experiments are situations created in one's mind, asking a question akin to "suppose you are in this situation, assuming such is true, what would follow?". They are usually created to investigate phenomena that are not readily experienced in every-day situations. Famous examples of such thought experiments are Schrödinger's cat, the EPR thought experiment, simple illustrations of time dilation, and so on. These usually lead to real experiments designed to verify that the conclusion (and therefore the assumptions) of the thought experiments are correct. The EPR thought experiment led to the Bell inequalities, which were then tested to various degrees of rigor, leading to the acceptance of the current formulation of quantum mechanics and probabilism as a working hypothesis. See also List of theoretical physicists Philosophy of physics Symmetry in quantum mechanics Timeline of developments in theoretical physics Notes  There is some debate as to whether or not theoretical physics uses mathematics to build intuition and illustrativeness to extract physical insight (especially when normal experience fails), rather than as a tool in formalizing theories. This links to the question of it using mathematics in a less formally rigorous, and more intuitive or heuristic way than, say, mathematical physics.  Sometimes the word "theory" can be used ambiguously in this sense, not to describe scientific theories, but research (sub)fields and programmes. Examples: relativity theory, quantum field theory, string theory.  The work of Johann Balmer and Johannes Rydberg in spectroscopy, and the semi-empirical mass formula of nuclear physics are good candidates for examples of this approach.  The Ptolemaic and Copernican models of the Solar system, the Bohr model of hydrogen atoms and nuclear shell model are good candidates for examples of this approach.  Arguably these are the most celebrated theories in physics: Newton's theory of gravitation, Einstein's theory of relativity and Maxwell's theory of electromagnetism share some of these attributes.  This approach is often favoured by (pure) mathematicians and mathematical physicists. The Los Alamos Laboratory, also known as Project Y, was a secret laboratory established by the Manhattan Project and operated by the University of California during World War II. Its mission was to design and build the first atomic bombs. Robert Oppenheimer was its first director, serving from 1943 to December 1945, when he was succeeded by Norris Bradbury. In order to enable scientists to freely discuss their work while preserving security, the laboratory was located in a remote part of New Mexico. The wartime laboratory occupied buildings that had once been part of the Los Alamos Ranch School. The development effort initially concentrated on a gun-type fission weapon using plutonium called Thin Man. In April 1944, the Los Alamos Laboratory determined that the rate of spontaneous fission in plutonium bred in a nuclear reactor was too great due to the presence of plutonium-240 and would cause a predetonation, a nuclear chain reaction before the core was fully assembled. Oppenheimer then reorganized the laboratory and orchestrated an all-out and ultimately successful effort on an alternative design proposed by John von Neumann, an implosion-type nuclear weapon, which was called Fat Man. A variant of the gun-type design known as Little Boy was developed using uranium-235. Chemists at the Los Alamos Laboratory developed methods of purifying uranium and plutonium, the latter a metal that only existed in microscopic quantities when Project Y began. Its metallurgists found that plutonium had unexpected properties, but were nonetheless able to cast it into metal spheres. The laboratory built the Water Boiler, an aqueous homogeneous reactor that was the third reactor in the world to become operational. It also researched the Super, a hydrogen bomb that would use a fission bomb to ignite a nuclear fusion reaction in deuterium and tritium. The Fat Man design was tested in the Trinity nuclear test in July 1945. Project Y personnel formed pit crews and assembly teams for the atomic bombings of Hiroshima and Nagasaki and participated in the bombing as weaponeers and observers. After the war ended, the laboratory supported the Operation Crossroads nuclear tests at Bikini Atoll. A new Z Division was created to control testing, stockpiling and bomb assembly activities, which were concentrated at Sandia Base. The Los Alamos Laboratory became Los Alamos Scientific Laboratory in 1947. Origins Nuclear fission and atomic bombs The discovery of the neutron by James Chadwick in 1932,[2] followed by the discovery of nuclear fission by chemists Otto Hahn and Fritz Strassmann in 1938,[3][4] and its explanation (and naming) by physicists Lise Meitner and Otto Frisch soon after,[5][6] opened up the possibility of a controlled nuclear chain reaction using uranium. At the time, few scientists in the United States thought that an atomic bomb was practical,[7] but the possibility that a German atomic bomb project would develop atomic weapons concerned refugee scientists from Nazi Germany and other fascist countries, leading to the drafting of the Einstein–Szilard letter to warn President Franklin D. Roosevelt. This prompted preliminary research in the United States, beginning in late 1939.[8] In nuclear fission, the atomic nucleus of a heavy element splits into two or more light ones when a neutron is captured. If more neutrons are emitted, a nuclear chain reaction becomes possible. Progress was slow in the United States, but in Britain, Otto Frisch and Rudolf Peierls, two refugee physicists from Germany at the University of Birmingham, examined the theoretical issues involved in developing, producing and using atomic bombs. They considered what would happen to a sphere of pure uranium-235, and found that not only could a chain reaction occur, but it might require as little as 1 kilogram (2.2 lb) of uranium-235 to unleash the energy of hundreds of tons of TNT. Their superior, Mark Oliphant, took the Frisch–Peierls memorandum to Sir Henry Tizard, the chairman of the Committee for the Scientific Survey of Air Warfare (CSSAW), who in turn passed it on to George Paget Thomson, to whom the CSSAW had delegated responsibility for uranium research.[9] CSSAW created the MAUD Committee to investigate.[10] In its final report in July 1941, the MAUD Committee concluded that an atomic bomb was not only feasible, but might be produced as early as 1943.[11] In response, the British government created a nuclear weapons project known as Tube Alloys.[12] There was still little urgency in the United States, which unlike Britain was not yet engaged in World War II, so Oliphant flew there in late August 1941,[13] and spoke to American scientists including his friend Ernest Lawrence at the University of California. He not only managed to convince them that an atomic bomb was feasible, but inspired Lawrence to convert his 37-inch (94 cm) cyclotron into a giant mass spectrometer for isotope separation,[14] a technique Oliphant had pioneered in 1934.[15] In turn, Lawrence brought in his friend and colleague Robert Oppenheimer to double-check the physics of the MAUD Committee report, which was discussed at a meeting at the General Electric Research Laboratory in Schenectady, New York, on 21 October 1941.[16] In December 1941, the S-1 Section of the Office of Scientific Research and Development (OSRD) placed Arthur H. Compton in charge of the design of the bomb.[17][18] He delegated the task of bomb design and research into fast neutron calculations—the key to calculations of critical mass and weapon detonation—to Gregory Breit, who was given the title of "Co-ordinator of Rapid Rupture", and Oppenheimer as an assistant. But Breit disagreed with other scientists working at the Metallurgical Laboratory, particularly Enrico Fermi, over the security arrangements,[19] and resigned on 18 May 1942.[20] Compton then appointed Oppenheimer to replace him.[21] John H. Manley, a physicist at the Metallurgical Laboratory, was assigned to assist Oppenheimer by contacting and coordinating experimental physics groups scattered across the country.[20] Oppenheimer and Robert Serber of the University of Illinois examined the problems of neutron diffusion—how neutrons moved in a nuclear chain reaction—and hydrodynamics—how the explosion produced by a chain reaction might behave.[22] Bomb design concepts In nuclear fusion, the nuclei of light elements are fused to create a heavier element. To review this work and the general theory of fission reactions, Oppenheimer and Fermi convened meetings at the University of Chicago in June and at the University of California in Berkeley, in July with theoretical physicists Hans Bethe, John Van Vleck, Edward Teller, Emil Konopinski, Robert Serber, Stan Frankel, and Eldred C. Nelson, the latter three former students of Oppenheimer, and experimental physicists Emilio Segrè, Felix Bloch, Franco Rasetti, John Manley, and Edwin McMillan. They tentatively confirmed that a fission bomb was theoretically possible.[23] There were still many unknown factors. The properties of pure uranium-235 were relatively unknown; even more so those of plutonium, a chemical element that had only recently been discovered by Glenn Seaborg and his team in February 1941, but which was theoretically fissile. The scientists at the Berkeley conference envisioned breeding plutonium in nuclear reactors from uranium-238 atoms that absorbed neutrons from fissioning uranium-235 atoms. At this point no reactor had been built, and only microscopic quantities of plutonium were available that had been produced by cyclotrons.[24] There were many ways of arranging the fissile material into a critical mass. The simplest was shooting a "cylindrical plug" into a sphere of "active material" with a "tamper"—dense material that would focus neutrons inward and keep the reacting mass together to increase its efficiency.[25] They also explored designs involving spheroids, a primitive form of "implosion" suggested by Richard C. Tolman, and the possibility of autocatalytic methods, which would increase the efficiency of the bomb as it exploded.[26] Considering the idea of the fission bomb theoretically settled—at least until more experimental data was available—the Berkeley conference then turned in a different direction. Edward Teller pushed for discussion of a more powerful bomb: the "Super", usually referred to today as a "hydrogen bomb", which would use the explosive force of a detonating fission bomb to ignite a nuclear fusion reaction between deuterium and tritium.[27] Teller proposed scheme after scheme, but Bethe rejected each one. The fusion idea was set aside to concentrate on producing fission bombs.[28] Teller also raised the speculative possibility that an atomic bomb might "ignite" the atmosphere because of a hypothetical fusion reaction of nitrogen nuclei,[29] but Bethe calculated that this could not happen,[30] and a report co-authored with Teller showed that "no self-propagating chain of nuclear reactions is likely to be started".[31] Bomb laboratory concept Oppenheimer's deft handling of the July conference impressed his colleagues; his insight and ability to handle even the most difficult people came as a surprise even to those who knew him well.[32] In the wake of the conference, Oppenheimer saw that while they had come to grips with the physics, considerable work was still required on the engineering, chemistry, metallurgy and ordnance aspects of building an atomic bomb. He became convinced that bomb design would require an environment where people could freely discuss problems and thereby reduce wasteful duplication of effort. He reasoned that this could best be reconciled with security by creating a central laboratory in an isolated location.[33][34] Brigadier General Leslie R. Groves Jr. became director of the Manhattan Project on 23 September 1942.[35] He visited Berkeley to look at Lawrence's calutrons, and met with Oppenheimer, who gave him a report on bomb design on 8 October.[36] Groves was interested in Oppenheimer's proposal to establish a separate bomb design laboratory. When they met again in Chicago a week later, he invited Oppenheimer to discuss the issue. Groves had to catch a train to New York, so he asked Oppenheimer to accompany him so that they could continue the discussion. Groves, Oppenheimer, and Colonel James C. Marshall and Lieutenant Colonel Kenneth Nichols all squeezed into a single compartment where they talked about how a bomb laboratory could be created, and how it would function.[33] Groves subsequently had Oppenheimer come to Washington, D.C., where the matter was discussed with Vannevar Bush, the director of the OSRD, and James B. Conant, the chairman of the National Defense Research Committee (NDRC). On 19 October, Groves approved the establishment of a bomb laboratory.[34] While Oppenheimer seemed the logical person to direct the new laboratory, which became known as Project Y, he had little administrative experience; Bush, Conant, Lawrence and Harold Urey all expressed reservations about this.[37] Moreover, unlike his other project leaders—Lawrence at the Berkeley Radiation Laboratory, Compton at the Metallurgical Project in Chicago, and Urey at the SAM Laboratories in New York—Oppenheimer did not have a Nobel Prize, raising concerns that he might not have the prestige to deal with distinguished scientists. There were also security concerns;[38] many of Oppenheimer's closest associates were active members of the Communist Party, including his wife Kitty,[39] girlfriend Jean Tatlock,[40] brother Frank, and Frank's wife Jackie.[41] In the end, Groves personally issued instructions to clear Oppenheimer on 20 July 1943.[38] Site selection Map of Los Alamos site, New Mexico, 1943–45 The idea of locating Project Y at the Metallurgical Laboratory in Chicago, or the Clinton Engineer Works in Oak Ridge, Tennessee, was considered, but in the end it was decided that a remote location would be best.[42] A site in the vicinity of Los Angeles was rejected on security grounds, and one near Reno, Nevada as being too inaccessible. On Oppenheimer's recommendation, the search was narrowed to the vicinity of Albuquerque, New Mexico, where Oppenheimer owned a ranch in the Sangre de Cristo Range.[43] The climate was mild, there were air and rail connections to Albuquerque, it was sufficiently distant from the West Coast of the United States for a Japanese attack not to be an issue, and the population density was low.[42] In October 1942, Major John H. Dudley of the Manhattan District (the military component of the Manhattan Project) surveyed sites around Gallup, Las Vegas, La Ventana, Jemez Springs, and Otowi,[44] and recommended the one near Jemez Springs.[42] On 16 November, Oppenheimer, Groves, Dudley and others toured the site. Oppenheimer feared that the high cliffs surrounding the site would make people feel claustrophobic, while the engineers were concerned with the possibility of flooding. The party then moved on to the Otowi site, the vicinity of the Los Alamos Ranch School. Oppenheimer was impressed by and expressed a strong preference for the site, citing its natural beauty and views of the Sangre de Cristo Mountains, which, he hoped, would inspire those who would work on the project.[45][46] The engineers were concerned about the poor access road, and whether the water supply would be adequate, but otherwise felt that it was ideal.[47] The United States Under Secretary of War, Robert P. Patterson, approved the acquisition of the site on 25 November 1942, authorizing $440,000 for the purchase of the site of 54,000 acres (22,000 ha), all but 8,900 acres (3,600 ha) of which were already owned by the Federal Government.[48] Secretary of Agriculture Claude R. Wickard granted use of some 45,100 acres (18,300 ha) of United States Forest Service land to the War Department "for so long as the military necessity continues".[49] The need for land for a new road, and later for a right of way for a 25-mile (40 km) power line, eventually brought wartime land purchases to 45,737 acres (18,509.1 ha), but only $414,971 was ultimately spent.[48] The big ticket items were the school, which cost $350,000, and the Anchor Ranch, which cost $25,000.[50] Both hired lawyers to negotiate deals with the government, but Hispanic homesteaders were paid as little as $7 an acre (equivalent to $118 in 2022).[51] Grazing permits were withdrawn, and private land was purchased or condemned under eminent domain using the authority of the Second War Powers Act.[52] Petitions of condemnation were worded to cover all mineral, water, timber and other rights, so private individuals would have no reason whatsoever to enter the area.[53] The site acquired an irregular shape due to abutting the Bandelier National Monument and a Native American sacred burial ground.[52] Construction An important consideration in the acquisition of the site was the existence of the Los Alamos Ranch School. This consisted of 54 buildings, of which 27 were houses, dormitories or other quarters providing 46,626 square feet (4,331.7 m2) of accommodation. The remaining buildings included a sawmill, ice house, barns, carpentry shop, stables and garages, all totalling 29,560 square feet (2,746 m2). At the nearby Anchor Ranch there were four houses and a barn.[54] Construction work was supervised by the Albuquerque Engineer District until 15 March 1944, when the Manhattan Engineer District assumed responsibility.[52] Willard C. Kruger and Associates of Santa Fe, New Mexico, was engaged as architect and engineer. Black & Veatch was brought in for the design of utilities in December 1945. The former was paid $743,706.68 and the latter $164,116 by the time the Manhattan Project ended at the end of 1946.[55] The Albuquerque District supervised $9.3 million of construction at Los Alamos, and the Manhattan District, another $30.4 million.[52] The initial work was contracted to the M. M. Sundt Company of Tucson, Arizona, with work commenced in December 1942. Groves initially allocated $300,000 for construction, three times Oppenheimer's estimate, with a planned completion date of 15 March 1943. It soon became clear that the scope of Project Y was far greater than expected, and by the time Sundt finished on 30 November 1943, over $7 million had been spent.[56] The Zia Company took over responsibility for maintenance in April 1946.[57] Four-family apartment units at Los Alamos Oppenheimer initially estimated that the work could be performed by 50 scientists and 50 technicians. Groves tripled this number to 300.[56] The actual population, including family members, was about 3,500 by the end of 1943, 5,700 by the end of 1944, 8,200 by the end of 1945, and 10,000 by the close of 1946.[58] The most desirable accommodation were the six existing log and stone cottages that had once housed the headmaster and the Los Alamos Ranch School faculty. They were the only dwellings at Los Alamos that had bathtubs, and became known as "Bathtub Row".[56][59] Oppenheimer lived on Bathtub Row; his next-door neighbor was Captain W. S. "Deak" Parsons, the head of the Ordnance and Engineering Division.[60] Parsons' house was slightly larger, because Parsons had two children and Oppenheimer, at that point, had only one.[61] After Bathtub Row, the next most desirable accommodation was the apartments built by Sundt. A typical two-storey building held four families. Each Sundt apartment had two or three bedrooms, a kitchen with a cranky black coal stove, and a small bathroom. J. E. Morgan and Sons supplied 56 prefabricated dwellings that became known as "Morganville". The Robert E. McKee Company built a part of the town known as "McKeeville".[56] In June through October 1943, and again in June and July 1944, numbers outstripped the available accommodation and personnel were temporarily lodged in Frijoles Canyon.[62] The houses at CEW and HEW were basic but of a higher standard (as specified by Nichols) than the houses at Los Alamos (as specified by Groves), but Nichols said to Los Alamos scientists that housing there was Groves' problem not his.[63] Rents were set based on the income of the occupant.[64] Transient visitors to Los Alamos were accommodated in the Fuller Lodge, the Guest Cottage or the Big House, which had once been part of the Los Alamos Ranch School.[65] A school was established in 1943, catering for both grade school and high school, and 140 children were enrolled; 350 by 1946. Education was free, as was a nursery school for working mothers.[66] With 18 grade-school teachers, 13 high-school teachers, and a superintendent, it enjoyed an excellent teacher:pupil ratio.[67] Numerous technical buildings were constructed. Most were of a semi-permanent type, using gypsum board. They were heated from a central heating plant. Initially this was Boiler House No. 1, which had two coal-fired boilers. This was replaced by Boiler House No. 2, which had six oil-fired boilers. In addition to the main site at Los Alamos, some 25 outlying sites were developed for experimental work.[68] The Technical Area at Los Alamos. There was a perimeter fence around the entire site, but also an inner fence shown here around the Technical Area. The growth of the town outpaced the sewage system,[68] and by late 1945 there were electrical outages. Lights had to be shut off during the day, and between 7 and 10 pm. Water also ran short. During the autumn of 1945, consumption was 585,000 US gallons (2,210,000 L) per day, but the water supply could furnish only 475,000 US gallons (1,800,000 L). On 19 December, pipes that had been laid above ground to save time in 1943 froze, cutting off the supply completely. Residents had to draw water from 15 tanker trucks that carried 300,000 US gallons (1,100,000 L) per day.[69] Because its name was secret, Los Alamos was referred to as "Site Y"; to residents it was known as "The Hill".[70] Because they lived on Federal land, the state of New Mexico did not allow residents of Los Alamos to vote in elections, although it did require them to pay state income taxes.[71][72] A drawn-out series of legal and legislative battles lay ahead before the residents of Los Alamos became fully-fledged citizens of New Mexico on 10 June 1949.[73] Birth certificates of babies born in Los Alamos during the war listed their place of birth as PO Box 1663 in Santa Fe. All letters and packages came through that address.[74] Initially Los Alamos was to have been a military laboratory with Oppenheimer and other researchers commissioned into the Army. Oppenheimer went so far as to order himself a lieutenant colonel's uniform, but two key physicists, Robert Bacher and Isidor Rabi, balked at the idea. Conant, Groves and Oppenheimer then devised a compromise whereby the laboratory was operated by the University of California.[75] Financial and procurement activities were the responsibility of the University of California under a 1 January 1943 letter of intent from the OSRD. This was superseded by a formal contract with the Manhattan District on 20 April 1943, which was backdated to 1 January. Financial operations were directed by the resident business officer, J. A. D. Muncy.[76] The intent was that it would be militarized when the time came to finally assemble the bomb, but by this time the Los Alamos Laboratory had grown so large that this was considered both impractical and unnecessary,[37] as the anticipated difficulties regarding civilians working on dangerous tasks had not occurred.[76] Organization Military Colonel John M. Harman was the first post commander at Los Alamos. He joined the Santa Fe office as a lieutenant colonel on 19 January 1943, and was promoted to colonel on 15 February.[77] Los Alamos officially became a military establishment on 1 April 1943, and he moved to Los Alamos on 19 April.[77][78] He was succeeded by Lieutenant Colonel C. Whitney Ashbridge, a graduate of the Los Alamos Ranch School,[79] in May 1943. In turn, Ashbridge was succeeded by Lieutenant Colonel Gerald R. Tyler in October 1944,[77][80] Colonel Lyle E. Seaman in November 1945, and Colonel Herb C. Gee in September 1946.[77] The post commander was answerable directly to Groves, and was responsible for the township, government property and the military personnel.[81] The main gate at Los Alamos Four military units were assigned to the post. The MP Detachment, 4817th Service Command Unit, arrived from Fort Riley, Kansas, in April 1943. Its initial strength was 7 officers and 196 enlisted men; by December 1946 it had 9 officers and 486 men, and was manning 44 guard posts 24 hours a day.[82] The Provisional Engineer Detachment (PED), 4817th Service Command Unit, was activated at Camp Claiborne, Louisiana, on 10 April 1943. These men performed jobs around the post such as working in the boiler plant, the motor pool and the mess halls. They also maintained the buildings and roads. It reached a peak strength of 465 men, and was disbanded on 1 July 1946.[83] The 1st Provisional Women's Army Auxiliary Corps (WAAC) Detachment was activated at Fort Sill, Oklahoma, on 17 April 1943. Its initial strength was just one officer and seven auxiliaries. The WAAC became the Women's Army Corps (WAC) on 24 August 1943, and the detachment became part of the 4817th Service Command Unit, with a strength of two officers and 43 enlisted women. They were sworn into the United States Army by Ashbridge. It reached a peak strength of about 260 women in August 1945. The WACs did a wider variety of jobs than the PED; some were cooks, drivers and telephone operators, while others served as librarians, clerks and hospital technicians. Some performed highly specialized scientific research inside the Technical Area.[83] The Special Engineer Detachment (SED) was activated in October 1943 as part of the 9812th Technical Service Unit. It was made up of men with technical skills or advanced education, and was mostly drawn from the defunct Army Specialized Training Program.[83] War Department policy forbade giving deferments from the draft to men under 22, so they were assigned to the SED.[84] It reached a peak strength of 1,823 men in August 1945. SED personnel worked in all areas of the Los Alamos Laboratory.[83] Civilian Passage between buildings A and B in the Technical Area As director of the Los Alamos Laboratory, Oppenheimer was no longer answerable to Compton, but reported directly to Groves.[78] He was responsible for the technical and scientific aspects of Project Y.[81] He assembled the nucleus of his staff from the groups that had been working for him on neutron calculations.[85] These included his secretary, Priscilla Greene,[86] Serber and McMillan from his own group, and Emilio Segrè and Joseph W. Kennedy's groups from the University of California, J. H. Williams' group from the University of Minnesota, Joe McKibben's group from the University of Wisconsin, Felix Bloch's group from Stanford University and Marshall Holloway's from Purdue University. He also secured the services of Hans Bethe and Robert Bacher from the Radiation Laboratory at MIT, Edward Teller, Robert F. Christy, Darol K. Froman, Alvin C. Graves and John H. Manley and his group from the Manhattan Project's Metallurgical Laboratory, and Robert R. Wilson and his group, which included Richard Feynman, that had been performing Manhattan Project research at Princeton University. They brought with them a great deal of valuable scientific equipment. Wilson's group dismantled the cyclotron at Harvard University and had it shipped to Los Alamos; McKibben's brought two Van de Graaff generators from Wisconsin; and Manley's brought the Cockcroft–Walton accelerator from the University of Illinois.[85] Communications with the outside world went through a single Forest Service line until April 1943,[87] when it was replaced by five Army telephone lines. This was increased to eight in March 1945.[88] There were also three teletypewriters with encoding machines. The first was installed in March 1943, and two more were added in May 1943. One was removed in November 1945.[88] There were telephones in the offices, but none in private residences, as the Army regarded this as a security hazard. There were some public phones in the township for emergencies. Since there was no way to prevent the lines being tapped, classified information could not be discussed over the phone lines. Initially the phone lines were operable only during business hours until enough WACs arrived to staff the switchboard around the clock.[89] Isidor Isaac Rabi, Dorothy McKibbin, Robert Oppenheimer and Victor Weisskopf at Oppenheimer's home in Los Alamos in 1944 Women at Los Alamos were encouraged to work, due to the shortage of labor and security concerns over bringing in local workers. About 60 wives of scientists were at work in Technical Area by September 1943. About 200 of the 670 workers in the laboratory, hospital and school were women in October 1944. Most worked in administration, but many women such as Lilli Hornig,[90] Jane Hamilton Hall,[91] and Peggy Titterton worked as scientists and technicians.[92] Charlotte Serber headed the A-5 (Library) Group.[93] A large group of women worked on numerical calculations in the T-5 (Computations) Group.[90] Dorothy McKibbin ran the Santa Fe office, which opened at 109 East Palace Avenue on 27 March 1943.[94] The Los Alamos Laboratory had a governing board, the members of which were Oppenheimer, Bacher, Bethe, Kennedy, D. L. Hughes (Personnel Director), D. P. Mitchell (Procurement Director) and Deak Parsons. McMillan, George Kistiakowsky and Kenneth Bainbridge were later added.[95] The laboratory was organized into five divisions: Administration (A), Theoretical (T) under Bethe, Experimental Physics (P) under Bacher, Chemistry and Metallurgy (CM) under Kennedy, and Ordnance and Engineering (E) under Parsons.[96][97] All the divisions expanded during 1943 and 1944, but T Division, despite trebling in size, remained the smallest, while E Division grew to be the largest. Security clearance was a problem. Scientists (including, at first, Oppenheimer) had to be given access to the Technical Area without proper clearance. In the interest of efficiency, Groves approved an abbreviated process by which Oppenheimer vouched for senior scientists, and three other employees were sufficient to vouch for a junior scientist or technician.[98] The Los Alamos Laboratory was reinforced by a British Mission under James Chadwick. The first to arrive were Otto Frisch and Ernest Titterton; later arrivals included Niels Bohr and his son Aage Bohr, and Sir Geoffrey Taylor, an expert on hydrodynamics who made a major contribution to the understanding of the Rayleigh–Taylor instability.[99] This instability at the interface between two fluids of different densities occurs when the lighter fluid is pushing the heavier,[100] and was vital to the interpretation of experiments with explosives, predicting the effects of an explosion, the design of the neutron initiators, and the design of the atomic bomb itself. Chadwick remained only for a few months; he was succeeded as head of the British Mission by Rudolf Peierls. The original idea, favored by Groves, was that the British scientists would work as a group under Chadwick, who would farm out work to them. This was soon discarded in favor of having the British Mission fully integrated into the laboratory. They worked in most of its divisions, only being excluded from plutonium chemistry and metallurgy.[101][99] With the passage of the Atomic Energy Act of 1946, known as the McMahon Act, all British government employees had to leave. All had left by the end of 1946, except for Titterton, who was granted a special dispensation, and remained until 12 April 1947. The British Mission ended when he departed.[102][103] Gun-type weapon design Research Los Alamos Technical Area Photograph of the Tech Area, with the buildings marked. They seem to be randomly scattered. Ashley Pond and the Fuller Lodge are in the background. Map of the Tech Area. In 1943, development efforts were directed to a gun-type fission weapon using plutonium called Thin Man.[104][105] The names for all three atomic bomb designs—Fat Man, Thin Man, and Little Boy—were chosen by Serber based on their shapes. Thin Man was a long device, and its name came from the Dashiell Hammett detective novel and series of movies of the same name. The Fat Man was round and fat, and was named after Sydney Greenstreet's "Kasper Gutman" character in The Maltese Falcon. Little Boy came last, and was named after Elisha Cook, Jr.'s character in the same film, as referred to by Humphrey Bogart.[106] A series of conferences in April and May 1943 laid out the laboratory's plan for the rest of the year. Oppenheimer estimated the critical mass of a uranium-235 gadget with a formula based on diffusion theory derived at Berkeley by Stan Frankel and E. C. Nelson. This gave a value for a uranium-235 gadget with a perfect tamper of 25 kg; but this was only an approximation. It was based on simplifying assumptions, notably that all neutrons had the same speed, that all collisions were elastic, that they were scattered isotropically, and that the mean free path of neutrons in the core and tamper were the same. Bethe's T Division, particularly Serber's T-2 (Diffusion Theory) Group and Feynman's T-4 (Diffusion Problems) Groups, would spend the next few months working on improved models.[107][108] Bethe and Feynman also developed a formula for the efficiency of the reaction.[109] No formula could be more accurate than the values put into it; the values for the cross sections were dubious, and had not yet been determined for plutonium. Measurement of these values would be a priority, but the laboratory possessed just 1 gram of uranium-235, and only a few micrograms of plutonium.[107] This task fell to Bacher's P Division. Williams P-2 (Electrostatic Generator) Group carried out the first experiment in July 1943, when it used the larger of the two Van de Graaff generators to measure the ratio of the neutron per fission in plutonium against that of uranium-235.[110] This involved some negotiation with the Metallurgical Laboratory to obtain 165 μg of plutonium, which was received at Los Alamos on 10 July 1943. Bacher was able to report that the number of neutrons per fission of plutonium-239 was 2.64 ± 0.2, about 1.2 times as much as uranium-235.[111] Titterton and Boyce McDaniel of Wilson's P-1 (Cyclotron) Group attempted to measure the time it took for prompt neutrons to be emitted from a uranium-235 nucleus when it fissions.[112] They calculated that most were emitted in less than 1 nanosecond. Subsequent experiments demonstrated that fission took less than a nanosecond too. Confirmation of the theorists' contention that the number of neutrons emitted per fission was the same for both fast and slow neutrons took longer, and was not completed until the autumn of 1944.[110] John von Neumann visited the Los Alamos Laboratory in September 1943 and participated in discussions of the damage that an atomic bomb would do. He explained that while the damage done by a small explosion was proportional to the impulse (the average pressure of the explosion times its duration), the damage from large explosions such as an atomic bomb would be determined by the peak pressure, which depends on the cube root of its energy. Bethe then calculated that a 10 kilotonnes of TNT (42 TJ) explosion would result in an overpressure of 0.1 standard atmospheres (10 kPa) at 3.5 kilometers (2.2 mi), and therefore result in severe damage within that radius. Von Neumann also suggested that, because pressure increases when shock waves bounce off solid objects, the damage could be increased if the bomb was detonated at an altitude comparable to the damage radius, approximately 1 to 2 kilometers (3,300 to 6,600 ft).[109][113] Development Parsons was appointed the head of Ordnance and Engineering Division in June 1943 on the recommendation of Bush and Conant.[114] To staff the division, Tolman, who acted as a coordinator of the gun development effort, brought in John Streib, Charles Critchfield and Seth Neddermeyer from the National Bureau of Standards.[115] The division was initially organized into five groups, with original group leaders being McMillan of the E-1 (Proving Ground) Group, Kenneth Bainbridge of the E-2 (Instrumentation) Group, Robert Brode of the E-3 (Fuse Development) Group, Critchfield of the E-4 (Projectile, Target, and Source) Group and Neddermeyer of the E-5 (Implosion) Group. Two more groups were added in the autumn of 1943, the E-7 (Delivery) Group under Norman Ramsey and the E-8 (Interior Ballistics) Group under Joseph O. Hirschfelder.[114] Long, tube-like casings. In the background are several ovoid casings and a tow truck. A row of Thin Man casings. Fat Man casings are visible in the background. The tow truck was used by the 216th Army Air Forces Base Unit to move them. A proving ground was established at the Anchor Ranch. The gun would be an unusual one, and it had to be designed in the absence of crucial data about the critical mass. The design criteria were that the gun would have a muzzle velocity of 3,000 feet per second (910 m/s); that the tube would weigh only 1 short ton (0.91 t) instead of the conventional 5 short tons (4.5 t) for a tube with that energy; that, as a consequence it would be made of alloyed steel; that it should have a maximum breech pressure of 75,000 pounds per square inch (520,000 kPa); and that it should have three independent primers. Because it would need to be fired only once, the barrel could be made lighter than the conventional gun. Nor did it require rifling or recoil mechanisms. Pressure curves were computed under Hirschfelder's supervision at the Geophysical Laboratory prior to his joining the Los Alamos Laboratory.[116] While they waited for the guns to be fabricated by the Naval Gun Factory, various propellants were tested. Hirschfelder sent John L. Magee to the Bureau of Mines' Experimental Mine at Bruceton, Pennsylvania to test the propellant and ignition system.[117] Test firing was conducted at the Anchor Ranch with a 3-inch (76 mm)/50 caliber gun. This allowed the fine-tuning of the testing instrumentation. The first two tubes arrived at Los Alamos on 10 March 1944, and test firing began at the Anchor Ranch under the direction of Thomas H. Olmstead, who had experience in such work at the Naval Proving Ground in Dahlgren, Virginia. The primers were tested and found to work at pressures up to 80,000 pounds per square inch (550,000 kPa). Brode's group investigated the fusing systems, testing radar altimeters, proximity fuses and barometric altimeter fuses.[118] Tests were conducted with a frequency modulated type radar altimeter known as AYD and a pulse type known as 718. The AYD modifications were made by the Norden Laboratories Corporation under an OSRD contract. When the manufacturer of 718, RCA, was contacted, it was learned that a new tail warning radar, AN/APS-13, later nicknamed Archie, was just entering production, which could be adapted for use as a radar altimeter. The third unit to be made was delivered to Los Alamos in April 1944. In May it was tested by diving an AT-11. This was followed by full-scale drop testing in June and July. These were very successful, whereas the AYD continued to suffer from problems. Archie was therefore adopted, although the scarcity of units in August 1944 precluded wholescale destructive testing.[118] Testing of Silverplate Boeing B-29 Superfortress aircraft with Thin Man bomb shapes was carried out at Muroc Army Air Field in March and June 1944.[119] Plutonium At a meeting of the S-1 Executive Committee on 14 November 1942, Chadwick had expressed a fear that the alpha particles emitted by plutonium could produce neutrons in light elements present as impurities, which in turn would produce fission in the plutonium and cause a predetonation, a chain reaction before the core was fully assembled. This had been considered by Oppenheimer and Seaborg the month before, and the latter had calculated that neutron emitters like boron had to be restricted to one part in a hundred billion. There was some doubt about whether a chemical process could be developed that could ensure this level of purity, and Chadwick brought the matter to the S-1 Executive Committee's attention for it to be considered further. Four days later, though, Lawrence, Oppenheimer, Compton and McMillan reported to Conant that they had confidence that the exacting purity requirement could be met.[120] A ring of electrorefined plutonium. It has a purity of 99.96%, weighs 5.3 kg, and is about 11 cm in diameter. It is enough plutonium for one bomb core. The ring shape helps with criticality safety. Only microscopic quantities of plutonium were available until the X-10 Graphite Reactor at the Clinton Engineer Works came online on 4 November 1943,[121][122] but there were already some worrying signs. When plutonium fluoride was produced at the Metallurgical Laboratory, it was sometimes light colored, and sometimes dark, although the chemical process was the same. When they managed to reduce it to plutonium metal in November 1943, the density was measured at 15 g/cm3, and a measurement using X-ray scattering techniques pointed to a density of 13 g/cm3. This was bad; it had been assumed that its density was the same as uranium, about 19 g/cm3. If these figures were correct, far more plutonium would be needed for a bomb. Kennedy disliked Seaborg's ambitious and attention-seeking manner, and with Arthur Wahl had devised a procedure for plutonium purification independent of Seaborg's group. When they got hold of a sample in February, this procedure was tested. That month the Metallurgical Laboratory announced that it had determined that there were two different fluorides: the light colored plutonium tetrafluoride (PuF4) and the dark plutonium trifluoride (PuF3). The chemists soon discovered how to make them selectively, and the former turned out to be easier to reduce to metal. Measurements in March 1944 indicated a density of between 19 and 20 g/cm3.[123] Eric Jette's CM-8 (Plutonium Metallurgy) Group began experimenting with plutonium metal after gram quantities were received at the Los Alamos Laboratory in March 1944. By heating it, the metallurgists discovered five temperatures between 137 and 580 °C (279 and 1,076 °F) at which it suddenly started absorbing heat without increasing in temperature. This was a strong indication of multiple allotropes of plutonium; but was initially considered too bizarre to be true. Further testing confirmed a state change around 135 °C (275 °F); it entered the δ phase, with a density of 16 g/cm3. Seaborg had claimed that plutonium had a melting point of around 950 to 1,000 °C (1,740 to 1,830 °F), about that of uranium, but the metallurgists at the Los Alamos Laboratory soon discovered that it melted at around 635 °C (1,175 °F). The chemists then turned to techniques for removing light element impurities from the plutonium; but on 14 July 1944, Oppenheimer informed Kennedy that this would no longer be required.[124] A graph showing change in density with increasing temperature upon sequential phase transitions between alpha, beta, gamma, delta, delta' and epsilon phases Plutonium has six allotropes at ambient pressure: alpha (α), beta (β), gamma (γ), delta (δ), delta prime (δ'), & epsilon (ε) [125] The notion of spontaneous fission had been raised by Niels Bohr and John Archibald Wheeler in their 1939 treatment of the mechanism of nuclear fission.[126] The first attempt to discover spontaneous fission in uranium was made by Willard Libby, but he failed to detect it.[127] It had been observed in Britain by Frisch and Titterton, and independently in the Soviet Union by Georgy Flyorov and Konstantin Petrzhak in 1940; the latter are generally credited with the discovery.[128][129] Compton had also heard from the French physicist Pierre Auger that Frédéric Joliot-Curie had detected what might have been spontaneous fission in polonium. If true, it might preclude the use of polonium in the neutron initiators; if true for plutonium, it might mean that the gun-type design would not work. The consensus at the Los Alamos Laboratory was that it was not true, and that Joliot-Curie's results had been distorted by impurities.[130] At the Los Alamos Laboratory, Emilio Segrè's P-5 (Radioactivity) Group set out to measure it in uranium-234, −235 and −238, plutonium, polonium, protactinium and thorium.[131] They were not too worried about the plutonium itself; their main concern was the issue Chadwick had raised about interaction with light element impurities. Segrè and his group of young physicists set up their experiment in an old Forest Service log cabin in Pajarito Canyon, about 14 miles (23 km) from the Technical Area, in order to minimize background radiation emanating for other research at the Los Alamos Laboratory.[132] By August 1943, they had good values for all the elements tested except for plutonium, which they were unable to measure accurately enough because the only sample they had was five 20 μg samples created by the 60-inch cyclotron at Berkeley.[133] They did observe that measurements taken at Los Alamos were greater than those made at Berkeley, which they attributed to cosmic rays, which are more numerous at Los Alamos, which is 7,300 feet (2,200 m) above sea level.[134] While their measurements indicated a spontaneous fission rate of 40 fissions per gram per hour, which was high but acceptable, the error margin was unacceptably large. In April 1944 they received a sample from the X-10 Graphite Reactor. Tests soon indicated 180 fissions per gram per hour, which was unacceptably high. It fell to Bacher to inform Compton, who was visibly shaken.[135] Suspicion fell on plutonium-240, an isotope that had not yet been discovered, but whose existence had been suspected, it being simply created by a plutonium-239 nucleus absorbing a neutron. What had not been suspected was its high spontaneous fission rate. Segrè's group measured it at 1.6 million fissions per gram per hour, compared with just 40 per gram per hour for plutonium-239. [136] This meant that reactor-bred plutonium was unsuitable for use in a gun-type weapon. The plutonium-240 would start the chain reaction too quickly, causing a predetonation that would release enough energy to disperse the critical mass before enough plutonium reacted. A faster gun was suggested but found to be impractical. So too was the possibility of separating the isotopes, as plutonium-240 is even harder to separate from plutonium-239 than uranium-235 from uranium-238.[137] Implosion-type weapon design Explosive lenses are used to compress a fissile core inside an implosion-type nuclear weapon. Work on an alternative method of bomb design, known as implosion, had begun by Neddermeyer's E-5 (Implosion) group. Serber and Tolman had conceived implosion during the April 1943 conferences as a means of assembling pieces of fissionable material together to form a critical mass. Neddermeyer took a different tack, attempting to crush a hollow cylinder into a solid bar.[138] The idea was to use explosives to crush a subcritical amount of fissile material into a smaller and denser form. When the fissile atoms are packed closer together, the rate of neutron capture increases, and they form a critical mass. The metal needs to travel only a very short distance, so the critical mass is assembled in much less time than it would take with the gun method.[139] At the time, the idea of using explosives in this manner was quite novel. To facilitate the work, a small plant was established at the Anchor Ranch for casting explosive shapes.[138] Throughout 1943, implosion was considered a backup project in case the gun-type proved impractical for some reason.[140] Theoretical physicists like Bethe, Oppenheimer and Teller were intrigued by the idea of a design of an atomic bomb that made more efficient use of fissile material, and permitted the use of material of lower purity. These were advantages of particular attraction to Groves. But while Neddermeyer's 1943 and early 1944 investigations into implosion showed promise, it was clear that the problem would be much more difficult from a theoretical and engineering perspective than the gun design. In July 1943, Oppenheimer wrote to John von Neumann, asking for his help, and suggesting that he visit Los Alamos where he could get "a better idea of this somewhat Buck Rogers project".[141] At the time, von Neumann was working for the Navy Bureau of Ordnance, Princeton University, the Army's Aberdeen Proving Ground and the NDRC. Oppenheimer, Groves and Parsons appealed to Tolman and Rear Admiral William R. Purnell to release von Neumann. He visited Los Alamos from 20 September to 4 October 1943. Drawing on his recent work with blast waves and shaped charges used in armor-piercing shells, he suggested using a high-explosive shaped charge to implode a spherical core. A meeting of the Governing Board on 23 September resolved to approach George Kistiakowsky, a renowned expert on explosives then working for OSRD, to join the Los Alamos Laboratory.[142] Although reluctant, he did so in November. He became a full-time staff member on 16 February 1944, becoming Parsons' deputy for implosion; McMillan became his deputy for the gun-type. The maximum size of the bomb was determined at this time from the size of the 5-by-12-foot (1.5 by 3.7 m) bomb bay of the B-29.[143] Diagram showing fast explosive, slow explosive, uranium tamper, plutonium core and neutron initiator. An implosion-type nuclear bomb. In the center is the neutron initiator (red). It is surrounded by the plutonium hemispheres. There is a small air gap (white, not in the original Fat Man design) and then the uranium tamper. Around that is the aluminium pusher (purple). This is encased in the explosive lenses (gold). Colors are the same as in the diagram opposite. By July 1944, Oppenheimer had concluded that plutonium could not be used in a gun design, and opted for implosion. The accelerated effort on an implosion design, codenamed Fat Man, began in August 1944 when Oppenheimer implemented a sweeping reorganization of the Los Alamos laboratory to focus on implosion.[144] Two new groups were created at Los Alamos to develop the implosion weapon, X (for explosives) Division headed by Kistiakowsky and G (for gadget) Division under Robert Bacher.[145][146] Although Teller was head of the T-1 (Implosion and Super) Group, Bethe considered that Teller was spending too much time on the Super, which had been given a low priority by Bethe and Oppenheimer. In June 1944, Oppenheimer created a dedicated Super Group under Teller, who was made directly responsible to Oppenheimer, and Peierls became head of the T-1 (Implosion) Group.[147][148] In September, Teller's group became the F-1 (Super and General Theory) Group, part of the Enrico Fermi's new F (Fermi) Division.[149] The new design that von Neumann and T Division, most notably Rudolf Peierls, devised used explosive lenses to focus the explosion onto a spherical shape using a combination of both slow and fast high explosives.[150] A visit by Sir Geoffrey Taylor in May 1944 raised questions about the stability of the interface between the core and the depleted uranium tamper. As a result, the design was made more conservative. The ultimate expression of this was the adoption of Christy's proposal that the core be solid instead of hollow.[151] The design of lenses that detonated with the proper shape and velocity turned out to be slow, difficult and frustrating.[150] Various explosives were tested before settling on composition B as the fast explosive and baratol as the slow explosive.[152] The final design resembled a soccer ball, with 20 hexagonal and 12 pentagonal lenses, each weighing about 80 pounds (36 kg). Getting the detonation just right required fast, reliable and safe electrical detonators, of which there were two for each lens for reliability.[153][154] It was therefore decided to use exploding-bridgewire detonators, a new invention developed at Los Alamos by a group led by Luis Alvarez. A contract for their manufacture was given to Raytheon.[155] To study the behavior of converging shock waves, Robert Serber devised the RaLa Experiment, which used the short-lived radioisotope lanthanum-140, a potent source of gamma radiation. The gamma ray source was placed in the center of a metal sphere surrounded by the explosive lenses, which in turn were inside in an ionization chamber. This allowed the taking of an X-ray movie of the implosion. The lenses were designed primarily using this series of tests.[156] In his history of the Los Alamos project, David Hawkins wrote: "RaLa became the most important single experiment affecting the final bomb design".[157] Within the explosives was the 4.5-inch (110 mm) thick aluminum pusher, which provided a smooth transition from the relatively low density explosive to the next layer, the 3-inch (76 mm) thick tamper of natural uranium. Its main job was to hold the critical mass together as long as possible, but it would also reflect neutrons back into the core. Some part of it might fission as well. To prevent predetonation by an external neutron, the tamper was coated in a thin layer of boron.[153] Norris Bradbury, group leader for bomb assembly, stands next to the partially assembled Gadget atop the Trinity test tower. Later, he became the director of Los Alamos vice Oppenheimer. A polonium-beryllium modulated neutron initiator, known as an "urchin" because its shape resembled a sea urchin,[158] was developed to start the chain reaction at precisely the right moment.[159] This work with the chemistry and metallurgy of radioactive polonium was directed by Charles Allen Thomas of the Monsanto Company and became known as the Dayton Project.[160] Testing required up to 500 curies per month of polonium, which Monsanto was able to deliver.[161] The whole assembly was encased in a duralumin bomb casing to protect it from bullets and flak.[153] The ultimate task of the metallurgists was to determine how to cast plutonium into a sphere. The brittle α phase that exists at room temperature changes to the plastic β phase at higher temperatures. Attention then shifted to the even more malleable δ phase that normally exists in the 300 to 450 °C (572 to 842 °F) range. It was found that this was stable at room temperature when alloyed with aluminum, but aluminum emits neutrons when bombarded with alpha particles, which would exacerbate the pre-ignition problem. The metallurgists then hit upon a plutonium–gallium alloy, which stabilized the δ phase and could be hot pressed into the desired spherical shape. As plutonium was found to corrode readily, the sphere was coated with nickel.[162] The work proved dangerous. By the end of the war, half the experienced chemists and metallurgists had to be removed from work with plutonium when unacceptably high levels of the element appeared in their urine.[163] A minor fire at Los Alamos in January 1945 led to a fear that a fire in the plutonium laboratory might contaminate the whole town, and Groves authorized the construction of a new facility for plutonium chemistry and metallurgy, which became known as the DP-site.[164] The hemispheres for the first plutonium pit (or core) were produced and delivered on 2 July 1945. Three more hemispheres followed on 23 July and were delivered three days later.[165] Little Boy Main article: Little Boy Following Oppenheimer's reorganization of the Los Alamos Laboratory in July 1944, the work on the uranium gun-type weapon was concentrated in Francis Birch's O-1 (Gun) Group.[166][167] The concept was pursued so that in case of a failure to develop an implosion bomb, at least the enriched uranium could be used.[168] Henceforth the gun-type had to work with enriched uranium only, and this allowed the Thin Man design to be greatly simplified. A high-velocity gun was no longer required, and a simpler weapon could be substituted, one short enough to fit into a B-29 bomb bay. The new design was called Little Boy.[169] A Little Boy unit on Tinian connected to test equipment, possibly to test or charge components within the device After repeated slippages, the first shipment of slightly enriched uranium (13 to 15 percent uranium-235) arrived from Oak Ridge in March 1944. Shipments of highly enriched uranium commenced in June 1944. Criticality experiments and the Water Boiler had priority, so the metallurgists did not receive any until August 1944. [170][171] In the meantime, the CM Division experimented with uranium hydride.[172] This was considered by T Division as a prospective active material. The idea was that the hydrogen's ability as a neutron moderator would compensate for the loss of efficiency, but, as Bethe later recalled, its efficiency was "negligible or less, as Feynman would say", and the idea was dropped by August 1944.[173] Frank Spedding's Ames Project had developed the Ames process, a method of producing uranium metal on an industrial scale, but Cyril Stanley Smith,[174] the CM Division's associate leader in charge of metallurgy,[175] was concerned about using it with highly enriched uranium due to the danger of forming a critical mass. Highly enriched uranium was also far more valuable than natural uranium, and he wanted to avoid the loss of even a milligram. He recruited Richard D. Baker, a chemist who had worked with Spedding, and together they adapted the Ames Process for use at the Los Alamos laboratory.[174] In February Baker and his group made twenty 360 gram reductions and twenty-seven 500 gram reductions with highly enriched uranium tetrafluoride.[176] Two types of gun design were produced: Type A was of high alloy steel, and Type B of more ordinary steel. Type B was chosen for production because it was lighter. The primers and propellant were the same as those previously chosen for Thin Man.[177] Scale test firing of the hollow projectile and target insert was conducted with the 3-inch/50 caliber gun and a 20 mm (0.79 in) Hispano cannon. Starting in December, test firing was done full-scale. Amazingly, the first test case produced turned out to be the best ever made. It was used in four test firings at the Anchor Ranch, and ultimately in the Little Boy used in the bombing of Hiroshima. The design specifications were completed in February 1945, and contracts were let to build the components. Three different plants were used so that no one would have a copy of the complete design. The gun and breech were made by the Naval Gun Factory in Washington, D.C.; the target, case and some other components were by the Naval Ordnance Plant in Center Line, Michigan; and the tail fairing and mounting brackets by the Expert Tool and Die Company in Detroit, Michigan.[178][177] Birch's tidy schedule was disrupted in December by Groves, who ordered Oppenheimer to give priority to the gun-type over implosion, so that the weapon would be ready by 1 July 1945.[179] The bomb, except for the uranium payload, was ready at the beginning of May 1945.[180] The uranium-235 projectile was completed on 15 June, and the target on 24 July.[181] The target and bomb pre-assemblies (partly assembled bombs without the fissile components) left Hunters Point Naval Shipyard, California, on 16 July aboard the cruiser USS Indianapolis, arriving 26 July.[182] The target inserts followed by air on 30 July.[181] Although all of its components had been tested in target and drop tests,[181] no full test of a gun-type nuclear weapon occurred before Hiroshima. There were several reasons for not testing a Little Boy type of device. Primarily, there was insufficient uranium-235.[183] Additionally, the weapon design was simple enough that it was only deemed necessary to do laboratory tests with the gun-type assembly. Unlike the implosion design, which required sophisticated coordination of shaped explosive charges, the gun-type design was considered almost certain to work.[184] Thirty-two drop tests were conducted at Wendover, and only once did the bomb fail to fire. One last-minute modification was made, to allow the powder bags of propellant that fired the gun to be loaded in the bomb bay.[177] The danger of accidental detonation made safety a concern. Little Boy incorporated basic safety mechanisms, but an accidental detonation could still occur. Tests were conducted to see whether a crash could drive the hollow "bullet" onto the "target" cylinder resulting in a massive release of radiation, or possibly nuclear detonation. These showed that this required an impact of 500 times that of gravity, which made it highly unlikely.[185] There was still concern that a crash and a fire could trigger the explosives.[186] If immersed in water, the uranium halves were subject to a neutron moderator effect. While this would not have caused an explosion, it could have created widespread radioactive contamination. For this reason, pilots were advised to crash on land rather than at sea.[185] Water boiler Water Boiler The Water Boiler was an aqueous homogeneous reactor, a type of nuclear reactor in which the nuclear fuel in the form of soluble uranium sulfate is dissolved in water.[187][188] Uranium sulfate was chosen instead of uranium nitrate because sulfur's neutron capture cross section is less than that of nitrogen.[189] The project was proposed by Bacher in April 1943 as part of an ongoing program of measuring critical masses in chain-reacting systems. He saw it also as a means of testing various materials in critical mass systems. T Division were opposed to the project, which was seen as a distraction from studies related to the form of chain reactions found in an atomic bomb, but Bacher prevailed on this point.[190] Calculations related to the Water Boiler did take up an inordinate amount of T Division's time in 1943.[188] The reactor theory developed by Fermi did not apply to the Water Boiler.[191] Little was known about building reactors in 1943. A group was created in Bacher's P Division, the P-7 (Water Boiler) Group, under the leadership of Donald Kerst,[192] that included Charles P. Baker, Gerhart Friedlander, Lindsay Helmholz, Marshall Holloway and Raemer Schreiber. Robert F. Christy from the T-1 Group provided support with the theoretical calculations, in particular, a calculation of the critical mass. He calculated that 600 grams of uranium-235 would form a critical mass in a tamper of infinite size. Initially it was planned to operate the Water Boiler at 10 kW, but Fermi and Samuel K. Allison visited in September 1943, and went over the proposed design. They pointed out the danger of decomposition of the uranium salt, and recommended heavier shielding. It was also noted that radioactive fission products would be created that would have to be chemically removed. As a consequence, it was decided that the Water Boiler would only run at 1 kW until more operating experience had been accumulated, and features needed for high power operation were shelved for the time being.[190] Christy also calculated the area that would become contaminated if an accidental explosion occurred. A site in Los Alamos Canyon was selected that was a safe distance from the township and downstream from the water supply. Known as Omega, it was approved by the Governing Board on 19 August 1943. The Water Boiler was not simple to construct. The two halves of the 12.0625-inch (306.39 mm) stainless steel sphere that was the boiler had to be arc welded because solder would be corroded by the uranium salt. The CM-7 (Miscellaneous Metallurgy) Group produced beryllia bricks for the Water Boiler's tamper in December 1943 and January 1944. They were hot pressed in graphite at 1,000 °C (1,830 °F) at 100 pounds per square inch (690 kPa) for 5 to 20 minutes. Some 53 bricks were made, shaped to fit around the boiler. The building at Omega Site was ready, if incomplete, by 1 February 1944, and the Water Boiler was fully assembled by 1 April. Sufficient enriched uranium had arrived by May to start it up, and it went critical on 9 May 1944.[190][193] It was only the third reactor in the world to do so, the first two being the Chicago Pile-1 reactor at the Metallurgical Laboratory and the X-10 Graphite Reactor at the Clinton Engineer Works.[187] Improved cross-section measurements allowed Christy to refine his criticality estimate to 575 grams. In fact, only 565 grams were required. The accuracy of his prediction surprised Christy more than anyone.[190] In September 1944, the P-7 (Water Boiler) Group became the F-2 (Water Boiler) Group, part of Fermi's F Division.[194] On completion of the planned series of experiments in June 1944, it was decided to rebuild it as a more powerful reactor. The original goal of 10 kW power was discarded in favor of 5 kW, which would keep the cooling requirements simple. It was estimated that it would have a neutron flux of 5 x 1010 neutrons per square centimeter per second. Water cooling was installed, along with additional control rods. This time uranium nitrate was used instead of uranium sulfate because the former could more easily be decontaminated. The tamper of beryllia bricks was surrounded with graphite blocks, as beryllia was hard to procure, and to avoid the (γ, n) reaction in the beryllium,[195] in which gamma rays produced by the reactor-generated neutrons:[196] 9 4Be  +  γ  → 8 4Be  +  n  - 1.66 MeV The reactor commenced operation in December 1944.[195] Super Main article: History of the Teller–Ulam design From the first, research into the Super was directed by Teller, who was its most enthusiastic proponent. Although this work was always considered secondary to the objective of developing a fission bomb, the prospect of creating more powerful bombs was sufficient to keep it going. The Berkeley summer conference had convinced Teller that the Super was technologically feasible. An important contribution was made by Emil Konopinski, who suggested that deuterium could more easily be ignited if it was mixed with tritium. Bethe noted that a tritium-deuterium (T-D) reaction releases five times as much energy as a deuterium-deuterium (D-D) reaction. This was not immediately followed up, because tritium was hard to obtain, and there were hopes that deuterium could be easily ignited by a fission bomb, but the cross sections of T-D and D-D were measured by Manley's group in Chicago and Holloway's at Purdue.[197] A group of men in shirtsleeves sitting on folding chairs The April 1946 colloquium on the Super. In the front row are (left to right) Norris Bradbury, John Manley, Enrico Fermi and J. M. B. Kellogg. Robert Oppenheimer, in dark coat, is behind Manley; to Oppenheimer's left is Richard Feynman. The Army officer on the left is Colonel Oliver Haywood. By September 1943, the values of the D-D and T-D had been revised upwards, raising hopes that a fusion reaction could be started at lower temperatures. Teller was sufficiently optimistic about the Super, and sufficiently concerned about reports that the Germans were interested in deuterium, to ask the Governing Board to raise its priority. The board agreed to some extent, but ruled that only one person could be spared to work on it full-time. Oppenheimer designated Konopinski, who would spend the rest of the war working on it. Nonetheless, in February 1944, Teller added Stanislaw Ulam, Jane Roberg, Geoffrey Chew, and Harold and Mary Argo to his T-1 Group. Ulam calculated the inverse Compton cooling, while Roberg worked out the ignition temperature of T-D mixtures.[197][198] Maria Goeppert joined the group in February 1945.[199] Teller argued for an increase in resources for Super research on the basis that it appeared to be far more difficult than anticipated. The board declined to do so, on the grounds that it was unlikely to bear fruit before the war ended, but did not cut it entirely. Indeed, Oppenheimer asked Groves to breed some tritium from deuterium in the X-10 Graphite Reactor. For some months Teller and Bethe argued about the priority of the Super research. In June 1944, Oppenheimer removed Teller and his Super Group from Bethe's T Division and placed it directly under himself. In September, it became the F-1 (Super) Group in Fermi' s F Division.[197][198] Over the following months, Super research continued unabated. It was calculated that burning 1 cubic meter (35 cu ft) of liquid deuterium would release the energy of 1 megatonne of TNT (4.2 PJ), enough to devastate 1,000 square miles (2,600 km2).[200] The Super Group was transferred back to T Division on 14 November 1945.[201] A colloquium on the Super was held at the Los Alamos Laboratory in April 1946 to review the work done during the war. Teller gave an outline of his "Classic Super" concept, and Nicholas Metropolis and Anthony L. Turkevich presented the results of calculations that had been made concerning thermonuclear reactions. The final report on the Super, issued in June and prepared by Teller and his group, remained upbeat about the prospect of the Super being successfully developed, although that impression was not universal among those present at the colloquium.[202] Work had to be curtailed in June 1946 due to the loss of staff.[203] By 1950, calculations would show that the Classic Super would not work; that it would not only be unable to sustain thermonuclear burning in the deuterium fuel, but would be unable to ignite it in the first place.[202] Trinity Main article: Trinity (nuclear test) Herbert Lehr and Harry Daghlian loading the assembled tamper plug containing the plutonium pit and initiator into a sedan for transport from the McDonald Ranch House to the Trinity shot tower Because of the complexity of an implosion-style weapon, it was decided that, despite the waste of fissile material, an initial test would be required. Groves approved the test, subject to the active material being recovered. Consideration was therefore given to a controlled fizzle, but Oppenheimer opted instead for a full-scale nuclear test, codenamed "Trinity".[204] In March 1944, responsibility for planning the test was assigned to Kenneth Bainbridge, a professor of physics at Harvard, working under Kistiakowsky. Bainbridge selected the bombing range near Alamogordo Army Airfield as the site for the test.[205] Bainbridge worked with Captain Samuel P. Davalos on the construction of the Trinity Base Camp and its facilities, which included barracks, warehouses, workshops, an explosive magazine and a commissary.[206] Groves did not relish the prospect of explaining the loss of a billion dollars worth of plutonium to a Senate committee, so a cylindrical containment vessel codenamed "Jumbo" was constructed to recover the active material in the event of a failure. Measuring 25 feet (7.6 m) long and 12 feet (3.7 m) wide, it was fabricated at great expense from 214 long tons (217 t) of iron and steel by Babcock & Wilcox in Barberton, Ohio. Brought in a special railroad car to a siding in Pope, New Mexico, it was transported the last 25 miles (40 km) to the test site on a trailer pulled by two tractors.[207] By the time it arrived, confidence in the implosion method was high enough, and the availability of plutonium was sufficient, that Oppenheimer decided not to use it. Instead, it was placed atop a steel tower 800 yards (730 m) from the weapon as a rough measure of how powerful the explosion would be. In the end, Jumbo survived, although its tower did not, adding credence to the belief that Jumbo would have successfully contained a fizzled explosion.[208][209] Men stand around a large oil-rig type structure. A large round object is being hoisted up. The explosives of "the gadget" were raised to the top of the tower for the final assembly. A pre-test explosion was conducted on 7 May 1945 to calibrate the instruments. A wooden test platform was erected 800 yards (730 m) from Ground Zero and piled with 108 short tons (98 t) of TNT spiked with nuclear fission products in the form of an irradiated uranium slug from the Hanford Site, which was dissolved and poured into tubing inside the explosive. This explosion was observed by Oppenheimer and Groves's new deputy commander, Brigadier General Thomas Farrell. The pre-test produced data that proved vital for the Trinity test.[209][210] For the actual test, the device, nicknamed "the gadget", was hoisted to the top of a 100-foot (30 m) steel tower, as detonation at that height would give a better indication of how the weapon would behave when dropped from a bomber. Detonation in the air maximized the energy applied directly to the target, and generated less nuclear fallout. The gadget was assembled under the supervision of Norris Bradbury at the nearby McDonald Ranch House on 13 July, and precariously winched up the tower the following day.[211] Observers included Bush, Chadwick, Conant, Farrell, Fermi, Groves, Lawrence, Oppenheimer and Tolman. At 05:30 on 16 July 1945 the gadget exploded with an energy equivalent of around 20 kilotons of TNT, leaving a crater of Trinitite (radioactive glass) in the desert 250 feet (76 m) wide. The shock wave was felt over 100 miles (160 km) away, and the mushroom cloud reached 7.5 miles (12.1 km) in height. It was heard as far away as El Paso, Texas, so Groves issued a cover story about an ammunition magazine explosion at Alamogordo Field.[212][213] Project Alberta Main article: Project Alberta Project Alberta, also known as Project A, was formed in March 1945, absorbing existing groups of Parsons's O Division that were working on bomb preparation and delivery. These included Ramsey's O-2 (Delivery) Group, Birch's O-1 (Gun) Group, Bainbridge's X-2 (Development, Engineering, and Tests) Group, Brode's O-3 (Fuse Development) Group and George Galloway's O-4 (Engineering) Group.[214][215] Its role was to support the bomb delivery effort. Parsons became the head of Project Alberta, with Ramsey as his scientific and technical deputy, and Ashworth as his operations officer and military alternate.[216] In all, Project Alberta consisted of 51 Army, Navy and civilian personnel.[217] The 1st Technical Service Detachment, to which the personnel of Project Alberta were administratively assigned, was commanded by Lieutenant Colonel Peer de Silva,[218] and provided security and housing services on Tinian.[219] There were two bomb assembly teams, a Fat Man Assembly Team under Commander Norris Bradbury and Roger Warner, and a Little Boy Assembly Team under Birch. Philip Morrison was the head of the Pit Crew, Bernard Waldman and Luis Alvarez led the Aerial Observation Team,[216][215] and Sheldon Dike was in charge of the Aircraft Ordnance Team.[219] Physicists Robert Serber and William Penney, and US Army Captain James F. Nolan, a medical expert, were special consultants.[220] All members of Project Alberta had volunteered for the mission.[221] Deak Parsons (right) supervises loading the Little Boy bomb into the B-29 Enola Gay. Norman Ramsey is on his left, with his back to the camera. Project Alberta proceeded with the plan to have the Little Boy ready by 1 August, and the first Fat Man ready for use as soon as possible after that.[222] In the meantime, a series of twelve combat missions were flown between 20 and 29 July against targets in Japan using high-explosive pumpkin bombs, versions of the Fat Man with the explosives, but not the fissile core.[223] Project Alberta's Sheldon Dike and Milo Bolstead flew on some of these missions, as did the British observer Group Captain Leonard Cheshire.[224] Four Little Boy pre-assemblies, L-1, L-2, L-5 and L-6 were expended in test drops.[225][226] The Little Boy team had the live bomb completely assembled and ready for use on 31 July.[227] The final item of preparation for the operation came on 29 July 1945. Orders for the attack were issued to General Carl Spaatz on 25 July under the signature of General Thomas T. Handy, the acting Chief of Staff of the United States Army, since General of the Army George C. Marshall was at the Potsdam Conference with President Harry S. Truman.[228] The order designated four targets: Hiroshima, Kokura, Niigata, and Nagasaki, and ordered the attack to be made "as soon as weather will permit after about 3 August".[229] Assembly of a Fat Man unit was a complex operation involving personnel from the High Explosive, Pit, Fusing and Firing teams. To prevent the assembly building from becoming overcrowded and thereby causing an accident, Parsons limited the numbers allowed inside at any time. Personnel waiting to perform a specific task had to wait their turn outside the building. The first Fat Man pre-assembly, known as F13, was assembled by 31 July, and expended in a drop test the next day. This was followed by F18 on 4 August, which was dropped the next day.[230] Three sets of Fat Man pre-assemblies, designated F31, F32, and F33, arrived on B-29s of the 509th Composite Group and 216th Army Air Forces Base Unit on 2 August. On inspection, the high explosive blocks of F32 were found to be badly cracked and unserviceable. The other two were assembled, with F33 earmarked for a rehearsal and F31 for operational use.[231] Fat Man bomb, with liquid asphalt sealant sprayed on the casing's seams, is readied on Tinian. Parsons, as the weaponeer, was in command of the Hiroshima mission. With Second Lieutenant Morris R. Jeppson of the 1st Ordnance Squadron, he inserted the Little Boy's powder bags in the Enola Gay's bomb bay in flight. Before climbing to altitude on approach to the target, Jeppson switched the three safety plugs between the electrical connectors of the internal battery and the firing mechanism from green to red. The bomb was then fully armed. Jeppson monitored its circuits.[232] Four other members of Project Alberta flew on the Hiroshima mission. Luis Alvarez, Harold Agnew and Lawrence H. Johnston were on the instrument plane The Great Artiste. They dropped "Bangometer" canisters to measure the force of the blast, but this was not used to calculate the yield at the time.[233] Bernard Waldman was the camera operator on the observation aircraft. He was equipped with a special high-speed Fastax movie camera with six seconds of film in order to record the blast. Waldman forgot to open the camera shutter, and no film was exposed.[234][235] Other members of the team flew to Iwo Jima in case Enola Gay was forced to land there, but this was not required.[236] Purnell, Parsons, Paul Tibbets, Spaatz and Curtis LeMay met on Guam on 7 August, the day after the Hiroshima attack, to discuss what should be done next. Parsons said that Project Alberta would have a Fat Man bomb ready by 11 August, as originally planned, but Tibbets pointed to weather reports indicating poor flying conditions on that day due to a storm, and asked if it could be readied by 9 August. Parsons agreed to do so.[237] For this mission, Ashworth was the weaponeer, with Lieutenant Philip M. Barnes, of the 1st Ordnance Squadron as assistant weaponeer on the B-29 Bockscar. Walter Goodman and Lawrence H. Johnston were on board the instrumentation aircraft, The Great Artiste. Leonard Cheshire and William Penney were on the observation plane Big Stink.[238] Robert Serber was supposed to be on board but was left behind by the aircraft commander because he had forgotten his parachute.[239] Health and safety A shack surrounded by pine trees. There is snow on the ground. A man and a woman in white lab coats are pulling on a rope, which is attached to a small trolley on a wooden platform. On top of the trolley is a large cylindrical object. Remote handling of a kilocurie source of radiolanthanum for a RaLa Experiment at Los Alamos A medical program was established at Los Alamos under Captain James F. Nolan of the United States Army Medical Corps.[240][241] Initially, a small five-bed infirmary was established for civilians, and a three-bed infirmary for military personnel. More serious cases were handled by the Army's Bruns General Hospital in Santa Fe, but this was soon regarded as unsatisfactory due to the loss of time due to the long trip, and security risks. Nolan recommended that the infirmaries be consolidated and expanded into a 60-bed hospital. A 54-bed hospital was opened in 1944, staffed by Army personnel. A dentist arrived in March 1944.[242] A Veterinary Corps officer, Captain J. Stevenson, had already been assigned to look after the guard dogs.[240] Laboratory facilities for medical research were limited, but some research was conducted into the effects of radiation, and the absorption and toxic effects of metals, particularly plutonium and beryllium, mainly as a result of accidents.[243] The Health Group began conducting urine tests of laboratory workers in early 1945, and many of these revealed dangerous levels of plutonium.[244] Work on the Water Boiler also occasionally exposed workers to dangerous fission products.[245] There were 24 fatal accidents at Los Alamos between its opening in 1943 and September 1946. Most involved construction workers. Four scientists died, including Harry Daghlian and Louis Slotin in criticality accidents involving the demon core.[246] Security Main article: Atomic spies On 10 March 1945, a Japanese fire balloon struck a power line, and the resulting power surge caused the Manhattan Project's reactors at the Hanford site to be temporarily shut down.[247] This generated great concern at Los Alamos that the site might come under attack. One night found everyone staring at a strange light in the sky. Oppenheimer later recalled this demonstrated that "even a group of scientists is not proof against the errors of suggestion and hysteria".[248] With so many people involved, security was a difficult task. A special Counter Intelligence Corps detachment was formed to handle the Manhattan Project's security issues.[249] By 1943, it was clear that the Soviet Union was attempting to penetrate the project.[250] The most successful Soviet spy was Klaus Fuchs of the British Mission.[251] The 1950 revelation of his espionage activities damaged the United States' nuclear cooperation with Britain and Canada.[252] Subsequently, other instances of espionage were uncovered, leading to the arrest of Harry Gold, David Greenglass and Ethel and Julius Rosenberg.[253] Other spies like Theodore Hall remained unknown for decades.[254] Post-war After the war ended on 14 August 1945, Oppenheimer informed Groves of his intention to resign as director of the Los Alamos Laboratory, but agreed to remain until a suitable replacement could be found. Groves wanted someone with both a solid academic background and a high standing within the project. Oppenheimer recommended Norris Bradbury. This was agreeable to Groves, who liked the fact that as a naval officer Bradbury was both a military man and a scientist. Bradbury accepted the offer on a six-month trial basis. Groves announced this at a meeting of division leaders on 18 September.[255] Parsons arranged for Bradbury to be quickly discharged from the Navy,[256] which awarded him the Legion of Merit for his wartime services.[257] He remained in the Naval Reserve, though, ultimately retiring in 1961 with the rank of captain.[258] On 16 October 1945, there was a ceremony at Los Alamos at which Groves presented the laboratory with the Army-Navy "E" Award, and presented Oppenheimer with a certificate of appreciation. Bradbury became the laboratory's second director the following day.[259][260] Bradbury (left) examines plans for new laboratory sites and permanent housing with Leslie Groves of the Armed Forces Special Weapons Project (center) and Eric Jette (right) in April 1947; Colonel Lyle E. Seeman stands behind Bradbury, second from the left. The first months of Bradbury's directorship were particularly trying. He had hoped that Atomic Energy Act of 1946 would be quickly passed by Congress and the wartime Manhattan Project would be superseded by a new, permanent organization. It soon became clear that this would take more than six months. President Harry S. Truman did not sign the act creating the Atomic Energy Commission into law until 1 August 1946, and it did not become active until 1 January 1947. In the meantime, Groves' legal authority to act was limited.[261] Most of the scientists at Los Alamos were eager to return to their laboratories and universities, and by February 1946 all of the wartime division heads had left, but a talented core remained. Darol Froman became head of Robert Bacher's G division, now renamed M Division. Eric Jette became responsible for Chemistry and Metallurgy, John H. Manley for Physics, George Placzek for Theory, Max Roy for Explosives, and Roger Wagner for Ordnance.[259] Z Division was created in July 1945 to control testing, stock piling, and bomb assembly activities. It was named after Jerrold R. Zacharias, its leader until 17 October 1945, when he returned to MIT, and was succeeded by Roger S. Warner. It moved to Sandia Base between March and July 1946, except for its Z-4 (Mechanical Engineering) Group, which followed in February 1947.[262] The number of personnel at the Los Alamos Laboratory plummeted from its wartime peak of over 3,000 to around 1,000, but many were still living in substandard temporary wartime accommodation.[261] Despite the reduced staff, Bradbury still had to provide support for Operation Crossroads, the nuclear tests in the Pacific.[263] Ralph A. Sawyer was appointed the Technical Director with Marshall Holloway from B Division and Roger Warner from Z Division as associate directors. Two ships were assigned for Los Alamos Laboratory personnel, the USS Cumberland Sound and Albemarle. Operation Crossroads cost the Los Alamos Laboratory over one million dollars, and the services of 150 personnel (about one-eighth of its staff) for nine months.[264] As the United States had only about ten atomic bombs in mid-1946 about one fifth of the stockpile was expended.[265] The Los Alamos Laboratory became the Los Alamos Scientific Laboratory in January 1947.[266] The contract with the University of California that had been negotiated in 1943 allowed the University to terminate it three months after the end of hostilities, and it served notice. There were concerns about the university operating a laboratory outside the state of California. The university was persuaded to rescind its notice,[267] and the operating contract was extended until July 1948.[268] Bradbury would remain director until 1970.[269] The total cost of Project Y up to the end of 1946 was $57.88 million (equivalent to $870 million in 2022).[65] The Manhattan Project was a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the U.S. Army Corps of Engineers. Nuclear physicist Robert Oppenheimer was the director of the Los Alamos Laboratory that designed the actual bombs. The Army component of the project was designated the Manhattan District as its first headquarters were in Manhattan; the placename gradually superseded the official codename, Development of Substitute Materials, for the entire project. Along the way, the project absorbed its earlier British counterpart, Tube Alloys. The Manhattan Project began modestly in 1939, but grew to employ nearly 130,000 people at its peak and cost nearly US$2 billion (equivalent to about $24 billion in 2021).[1] Over 90 percent of the cost was for building factories and to produce fissile material, with less than 10 percent for development and production of the weapons. Research and production took place at more than thirty sites across the United States, the United Kingdom, and Canada. The project led to the development of two types of atomic bombs, both developed concurrently, during the war: a relatively simple gun-type fission weapon and a more complex implosion-type nuclear weapon. The Thin Man gun-type design proved impractical to use with plutonium, so a simpler gun-type design called Little Boy was developed that used uranium-235, an isotope that makes up only 0.7 percent of natural uranium. Because it is chemically identical to the most common isotope, uranium-238, and has almost the same mass, separating the two proved difficult. Three methods were employed for uranium enrichment: electromagnetic, gaseous and thermal. Most of this work was carried out at the Clinton Engineer Works at Oak Ridge, Tennessee. In parallel with the work on uranium was an effort to produce plutonium, which researchers at the University of California, Berkeley, discovered in 1940. After the feasibility of the world's first artificial nuclear reactor, the Chicago Pile-1, was demonstrated in 1942 at the Metallurgical Laboratory in the University of Chicago, the project designed the X-10 Graphite Reactor at Oak Ridge and the production reactors at the Hanford Site in Washington state, in which uranium was irradiated and transmuted into plutonium. The plutonium was then chemically separated from the uranium, using the bismuth phosphate process. The Fat Man plutonium implosion-type weapon was developed in a concerted design and development effort by the Los Alamos Laboratory. The project was also charged with gathering intelligence on the German nuclear weapon project. Through Operation Alsos, Manhattan Project personnel served in Europe, sometimes behind enemy lines, where they gathered nuclear materials and documents, and rounded up German scientists. Despite the Manhattan Project's tight security, Soviet atomic spies successfully penetrated the program. The first nuclear device ever detonated was an implosion-type bomb during the Trinity test, conducted at New Mexico's Alamogordo Bombing and Gunnery Range on 16 July 1945. Little Boy and Fat Man bombs were used a month later in the atomic bombings of Hiroshima and Nagasaki, respectively, with Manhattan Project personnel serving as bomb assembly technicians and weaponeers on the attack aircraft. In the immediate postwar years, the Manhattan Project conducted weapons testing at Bikini Atoll as part of Operation Crossroads, developed new weapons, promoted the development of the network of national laboratories, supported medical research into radiology and laid the foundations for the nuclear navy. It maintained control over American atomic weapons research and production until the formation of the United States Atomic Energy Commission in January 1947. Origins For a chronological guide, see Timeline of the Manhattan Project. The discovery of nuclear fission by German chemists Otto Hahn and Fritz Strassmann in 1938, and its theoretical explanation by Lise Meitner and Otto Frisch, made the development of an atomic bomb a theoretical possibility. There were fears that a German atomic bomb project would develop one first, especially among scientists who were refugees from Nazi Germany and other fascist countries.[2] In August 1939, Hungarian-born physicists Leo Szilard and Eugene Wigner drafted the Einstein–Szilard letter, which warned of the potential development of "extremely powerful bombs of a new type". It urged the United States to take steps to acquire stockpiles of uranium ore and accelerate the research of Enrico Fermi and others into nuclear chain reactions. They had it signed by Albert Einstein and delivered to President Franklin D. Roosevelt. Roosevelt called on Lyman Briggs of the National Bureau of Standards to head the Advisory Committee on Uranium to investigate the issues raised by the letter. Briggs held a meeting on 21 October 1939, which was attended by Szilárd, Wigner and Edward Teller.[3] The committee reported back to Roosevelt in November that uranium "would provide a possible source of bombs with a destructiveness vastly greater than anything now known."[4] Enrico Fermi, John R. Dunning, and Dana P. Mitchell in front of the cyclotron in the basement of Pupin Hall at Columbia University In February 1940, the U.S. Navy awarded Columbia University $6,000 in funding,[5] most of which Enrico Fermi and Szilard spent on purchasing graphite. A team of Columbia professors including Fermi, Szilard, Eugene T. Booth and John Dunning created the first nuclear fission reaction in the Americas, verifying the work of Hahn and Strassmann. The same team subsequently built a series of prototype nuclear reactors (or "piles" as Fermi called them) in Pupin Hall at Columbia, but were not yet able to achieve a chain reaction.[6] The Advisory Committee on Uranium became the National Defense Research Committee (NDRC) on Uranium when that organization was formed on 27 June 1940.[7] Briggs proposed spending $167,000 on research into uranium, particularly the uranium-235 isotope, and plutonium, which was discovered in 1940 at the University of California.[8][note 1] On 28 June 1941, Roosevelt signed Executive Order 8807, which created the Office of Scientific Research and Development (OSRD),[11] with Vannevar Bush as its director. The office was empowered to engage in large engineering projects in addition to research.[8] The NDRC Committee on Uranium became the S-1 Section of the OSRD; the word "uranium" was dropped for security reasons.[12] In Britain, Frisch and Rudolf Peierls at the University of Birmingham had made a breakthrough investigating the critical mass of uranium-235 in June 1939.[13] Their calculations indicated that it was within an order of magnitude of 10 kilograms (22 lb), which was small enough to be carried by a bomber of the day.[14] Their March 1940 Frisch–Peierls memorandum initiated the British atomic bomb project and its MAUD Committee,[15] which unanimously recommended pursuing the development of an atomic bomb.[14] In July 1940, Britain had offered to give the United States access to its scientific research,[16] and the Tizard Mission's John Cockcroft briefed American scientists on British developments. He discovered that the American project was smaller than the British, and not as far advanced.[17] As part of the scientific exchange, the MAUD Committee's findings were conveyed to the United States. One of its members, the Australian physicist Mark Oliphant, flew to the United States in late August 1941 and discovered that data provided by the MAUD Committee had not reached key American physicists. Oliphant then set out to find out why the committee's findings were apparently being ignored. He met with the Uranium Committee and visited Berkeley, California, where he spoke persuasively to Ernest O. Lawrence. Lawrence was sufficiently impressed to commence his own research into uranium. He in turn spoke to James B. Conant, Arthur H. Compton and George B. Pegram. Oliphant's mission was therefore a success; key American physicists were now aware of the potential power of an atomic bomb.[18][19] On 9 October 1941, President Roosevelt approved the atomic program after he convened a meeting with Vannevar Bush and Vice President Henry A. Wallace. To control the program, he created a Top Policy Group consisting of himself—although he never attended a meeting—Wallace, Bush, Conant, Secretary of War Henry L. Stimson, and the Chief of Staff of the Army, General George C. Marshall. Roosevelt chose the Army to run the project rather than the Navy, because the Army had more experience with management of large-scale construction projects. He also agreed to coordinate the effort with that of the British, and on 11 October he sent a message to Prime Minister Winston Churchill, suggesting that they correspond on atomic matters.[20] Feasibility Proposals Six men in suits sitting on chairs, smiling and laughing March 1940 meeting at Berkeley, California: Ernest O. Lawrence, Arthur H. Compton, Vannevar Bush, James B. Conant, Karl T. Compton, and Alfred L. Loomis The S-1 Committee held its meeting on 18 December 1941 "pervaded by an atmosphere of enthusiasm and urgency"[21] in the wake of the attack on Pearl Harbor and the subsequent United States declaration of war upon Japan and then on Germany.[22] Work was proceeding on three different techniques for isotope separation to separate uranium-235 from the more abundant uranium-238. Lawrence and his team at the University of California investigated electromagnetic separation, while Eger Murphree and Jesse Wakefield Beams's team looked into gaseous diffusion at Columbia University, and Philip Abelson directed research into thermal diffusion at the Carnegie Institution of Washington and later the Naval Research Laboratory.[23] Murphree was also the head of an unsuccessful separation project using gas centrifuges.[24] Meanwhile, there were two lines of research into nuclear reactor technology, with Harold Urey continuing research into heavy water at Columbia, while Arthur Compton brought the scientists working under his supervision from Columbia, California and Princeton University to join his team at the University of Chicago, where he organized the Metallurgical Laboratory in early 1942 to study plutonium and reactors using graphite as a neutron moderator.[25] Briggs, Compton, Lawrence, Murphree, and Urey met on 23 May 1942, to finalize the S-1 Committee recommendations, which called for all five technologies to be pursued. This was approved by Bush, Conant, and Brigadier General Wilhelm D. Styer, the chief of staff of Major General Brehon B. Somervell's Services of Supply, who had been designated the Army's representative on nuclear matters.[23] Bush and Conant then took the recommendation to the Top Policy Group with a budget proposal for $54 million for construction by the United States Army Corps of Engineers, $31 million for research and development by OSRD and $5 million for contingencies in fiscal year 1943. The Top Policy Group in turn sent it on 17 June 1942, to the President, who approved it by writing "OK FDR" on the document.[23] Bomb design concepts A series of doodles Different fission bomb assembly methods explored during the July 1942 conference Compton asked theoretical physicist J. Robert Oppenheimer of the University of California to take over research into fast neutron calculations—the key to calculations of critical mass and weapon detonation—from Gregory Breit, who had quit on 18 May 1942 because of concerns over lax operational security.[26] John H. Manley, a physicist at the Metallurgical Laboratory, was assigned to assist Oppenheimer by contacting and coordinating experimental physics groups scattered across the country.[27] Oppenheimer and Robert Serber of the University of Illinois examined the problems of neutron diffusion—how neutrons moved in a nuclear chain reaction—and hydrodynamics—how the explosion produced by a chain reaction might behave. To review this work and the general theory of fission reactions, Oppenheimer and Fermi convened meetings at the University of Chicago in June and at the University of California in July 1942 with theoretical physicists Hans Bethe, John Van Vleck, Edward Teller, Emil Konopinski, Robert Serber, Stan Frankel, and Eldred C. (Carlyle) Nelson, the latter three former students of Oppenheimer, and experimental physicists Emilio Segrè, Felix Bloch, Franco Rasetti, John Henry Manley, and Edwin McMillan. They tentatively confirmed that a fission bomb was theoretically possible.[28] There were still many unknown factors. The properties of pure uranium-235 were relatively unknown, as were those of plutonium, an element that had only been discovered in February 1941 by Glenn Seaborg and his team. The scientists at the (July 1942) Berkeley conference envisioned creating plutonium in nuclear reactors where uranium-238 atoms absorbed neutrons that had been emitted from fissioning uranium-235 atoms. At this point no reactor had been built, and only tiny quantities of plutonium were available from cyclotrons at institutions such as Washington University in St. Louis.[29] Even by December 1943, only two milligrams had been produced.[30] There were many ways of arranging the fissile material into a critical mass. The simplest was shooting a "cylindrical plug" into a sphere of "active material" with a "tamper"—dense material that would focus neutrons inward and keep the reacting mass together to increase its efficiency.[31] They also explored designs involving spheroids, a primitive form of "implosion" suggested by Richard C. Tolman, and the possibility of autocatalytic methods, which would increase the efficiency of the bomb as it exploded.[32] Considering the idea of the fission bomb theoretically settled—at least until more experimental data was available—the 1942 Berkeley conference then turned in a different direction. Edward Teller pushed for discussion of a more powerful bomb: the "super", now usually referred to as a "hydrogen bomb", which would use the explosive force of a detonating fission bomb to ignite a nuclear fusion reaction in deuterium and tritium.[33] Teller proposed scheme after scheme, but Bethe refused each one. The fusion idea was put aside to concentrate on producing fission bombs.[34] Teller also raised the speculative possibility that an atomic bomb might "ignite" the atmosphere because of a hypothetical fusion reaction of nitrogen nuclei.[note 2] Bethe calculated that it could not happen,[36] and a report co-authored by Teller showed that "no self-propagating chain of nuclear reactions is likely to be started."[37] In Serber's account, Oppenheimer mentioned the possibility of this scenario to Arthur Compton, who "didn't have enough sense to shut up about it. It somehow got into a document that went to Washington" and was "never laid to rest".[note 3] Organization Manhattan District The Chief of Engineers, Major General Eugene Reybold, selected Colonel James C. Marshall to head the Army's part of the project in June 1942. Marshall created a liaison office in Washington, D.C., but established his temporary headquarters on the 18th floor of 270 Broadway in New York, where he could draw on administrative support from the Corps of Engineers' North Atlantic Division. It was close to the Manhattan office of Stone & Webster, the principal project contractor, and to Columbia University. He had permission to draw on his former command, the Syracuse District, for staff, and he started with Lieutenant Colonel Kenneth Nichols, who became his deputy.[39][40] Organization chart of the project, showing project headquarters divisions at the top, Manhattan District in the middle, and field offices at the bottom Manhattan Project Organization Chart, 1 May 1946 Because most of his task involved construction, Marshall worked in cooperation with the head of the Corps of Engineers Construction Division, Major General Thomas M. Robbins, and his deputy, Colonel Leslie Groves. Reybold, Somervell, and Styer decided to call the project "Development of Substitute Materials", but Groves felt that this would draw attention. Since engineer districts normally carried the name of the city where they were located, Marshall and Groves agreed to name the Army's component of the project the Manhattan District. This became official on 13 August when Reybold issued the order creating the new district. Informally, it was known as the Manhattan Engineer District, or MED. Unlike other districts, it had no geographic boundaries, and Marshall had the authority of a division engineer. Development of Substitute Materials remained as the official codename of the project as a whole, but was supplanted over time by "Manhattan".[40][41] Marshall later conceded that, "I had never heard of atomic fission but I did know that you could not build much of a plant, much less four of them for $90 million."[42] A single TNT plant that Nichols had recently built in Pennsylvania had cost $128 million.[43] Nor were they impressed with estimates to the nearest order of magnitude, which Groves compared with telling a caterer to prepare for between ten and a thousand guests.[44] A survey team from Stone & Webster had already scouted a site for the production plants. The War Production Board recommended sites around Knoxville, Tennessee, an isolated area where the Tennessee Valley Authority could supply ample electric power and the rivers could provide cooling water for the reactors. After examining several sites, the survey team selected one near Elza, Tennessee. Conant advised that it be acquired at once and Styer agreed but Marshall temporized, awaiting the results of Conant's reactor experiments before taking action.[45] Of the prospective processes, only Lawrence's electromagnetic separation appeared sufficiently advanced for construction to commence.[46] Marshall and Nichols began assembling the resources they would need. The first step was to obtain a high priority rating for the project. The top ratings were AA-1 through AA-4 in descending order, although there was also a special AAA rating reserved for emergencies. Ratings AA-1 and AA-2 were for essential weapons and equipment, so Colonel Lucius D. Clay, the deputy chief of staff at Services and Supply for requirements and resources, felt that the highest rating he could assign was AA-3, although he was willing to provide a AAA rating on request for critical materials if the need arose.[47] Nichols and Marshall were disappointed; AA-3 was the same priority as Nichols' TNT plant in Pennsylvania.[48] Military Policy Committee A man smiling in a suit in suit and one in a uniform chat around a pile of twisted metal. Oppenheimer and Groves at the remains of the Trinity test in September 1945, two months after the test blast and just after the end of World War II. The white overshoes prevented fallout from sticking to the soles of their shoes.[49] Vannevar Bush became dissatisfied with Colonel Marshall's failure to get the project moving forward expeditiously, specifically the failure to acquire the Tennessee site, the low priority allocated to the project by the Army and the location of his headquarters in New York City.[50] Bush felt that more aggressive leadership was required, and spoke to Harvey Bundy and Generals Marshall, Somervell, and Styer about his concerns. He wanted the project placed under a senior policy committee, with a prestigious officer, preferably Styer, as overall director.[48] Somervell and Styer selected Groves for the post, informing him on 17 September of this decision, and that General Marshall ordered that he be promoted to brigadier general,[51] as it was felt that the title "general" would hold more sway with the academic scientists working on the Manhattan Project.[52] Groves' orders placed him directly under Somervell rather than Reybold, with Colonel Marshall now answerable to Groves.[53] Groves established his headquarters in Washington, D.C., on the fifth floor of the New War Department Building, where Colonel Marshall had his liaison office.[54] He assumed command of the Manhattan Project on 23 September 1942. Later that day, he attended a meeting called by Stimson, which established a Military Policy Committee, responsible to the Top Policy Group, consisting of Bush (with Conant as an alternate), Styer and Rear Admiral William R. Purnell.[51] Tolman and Conant were later appointed as Groves' scientific advisers.[55] On 19 September, Groves went to Donald Nelson, the chairman of the War Production Board, and asked for broad authority to issue a AAA rating whenever it was required. Nelson initially balked but quickly caved in when Groves threatened to go to the President.[56] Groves promised not to use the AAA rating unless it was necessary. It soon transpired that for the routine requirements of the project the AAA rating was too high but the AA-3 rating was too low. After a long campaign, Groves finally received AA-1 authority on 1 July 1944.[57] According to Groves, "In Washington you became aware of the importance of top priority. Most everything proposed in the Roosevelt administration would have top priority. That would last for about a week or two and then something else would get top priority".[58] One of Groves' early problems was to find a director for Project Y, the group that would design and build the bomb. The obvious choice was one of the three laboratory heads, Urey, Lawrence, or Compton, but they could not be spared. Compton recommended Oppenheimer, who was already intimately familiar with the bomb design concepts. However, Oppenheimer had little administrative experience, and, unlike Urey, Lawrence, and Compton, had not won a Nobel Prize, which many scientists felt that the head of such an important laboratory should have. There were also concerns about Oppenheimer's security status, as many of his associates were communists, including his wife, Kitty (Katherine Oppenheimer); his girlfriend, Jean Tatlock; and his brother, Frank Oppenheimer. A long conversation on a train in October 1942 convinced Groves and Nichols that Oppenheimer thoroughly understood the issues involved in setting up a laboratory in a remote area and should be appointed as its director. Groves personally waived the security requirements and issued Oppenheimer a clearance on 20 July 1943.[59][60] Collaboration with the United Kingdom Main article: British contribution to the Manhattan Project The British and Americans exchanged nuclear information but did not initially combine their efforts. Britain rebuffed attempts by Bush and Conant in 1941 to strengthen cooperation with its own project, codenamed Tube Alloys, because it was reluctant to share its technological lead and help the United States develop its own atomic bomb.[61] An American scientist who brought a personal letter from Roosevelt to Churchill offering to pay for all research and development in an Anglo-American project was poorly treated, and Churchill did not reply to the letter. The United States as a result decided as early as April 1942 that if its offer was rejected, they should proceed alone.[62] The British, who had made significant contributions early in the war, did not have the resources to carry through such a research program while fighting for their survival. As a result, Tube Alloys soon fell behind its American counterpart.[63] and on 30 July 1942, Sir John Anderson, the minister responsible for Tube Alloys, advised Churchill that: "We must face the fact that ... [our] pioneering work ... is a dwindling asset and that, unless we capitalise it quickly, we shall be outstripped. We now have a real contribution to make to a 'merger.' Soon we shall have little or none."[64] That month Churchill and Roosevelt made an informal, unwritten agreement for atomic collaboration.[65] A large man in uniform and a bespectacled thin man in a suit and tie sit at a desk. Groves confers with James Chadwick, the head of the British Mission. The opportunity for an equal partnership no longer existed, however, as shown in August 1942 when the British unsuccessfully demanded substantial control over the project while paying none of the costs. By 1943 the roles of the two countries had reversed from late 1941;[62] in January Conant notified the British that they would no longer receive atomic information except in certain areas. While the British were shocked by the abrogation of the Churchill-Roosevelt agreement, head of the Canadian National Research Council C. J. Mackenzie was less surprised, writing "I can't help feeling that the United Kingdom group [over] emphasizes the importance of their contribution as compared with the Americans."[65] As Conant and Bush told the British, the order came "from the top".[66] The British bargaining position had worsened; the American scientists had decided that the United States no longer needed outside help, and they wanted to prevent Britain exploiting post-war commercial applications of atomic energy. The committee supported, and Roosevelt agreed to, restricting the flow of information to what Britain could use during the war—especially not bomb design—even if doing so slowed down the American project. By early 1943 the British stopped sending research and scientists to America, and as a result the Americans stopped all information sharing. The British considered ending the supply of Canadian uranium and heavy water to force the Americans to again share, but Canada needed American supplies to produce them.[67] They investigated the possibility of an independent nuclear program, but determined that it could not be ready in time to affect the outcome of the war in Europe.[68] By March 1943 Conant decided that British help would benefit some areas of the project. James Chadwick and one or two other British scientists were important enough that the bomb design team at Los Alamos needed them, despite the risk of revealing weapon design secrets.[69] In August 1943 Churchill and Roosevelt negotiated the Quebec Agreement, which resulted in a resumption of cooperation[70] between scientists working on the same problem. Britain, however, agreed to restrictions on data on the building of large-scale production plants necessary for the bomb.[71] The subsequent Hyde Park Agreement in September 1944 extended this cooperation to the postwar period.[72] The Quebec Agreement established the Combined Policy Committee to coordinate the efforts of the United States, United Kingdom and Canada. Stimson, Bush and Conant served as the American members of the Combined Policy Committee, Field Marshal Sir John Dill and Colonel J. J. Llewellin were the British members, and C. D. Howe was the Canadian member.[73] Llewellin returned to the United Kingdom at the end of 1943 and was replaced on the committee by Sir Ronald Ian Campbell, who in turn was replaced by the British Ambassador to the United States, Lord Halifax, in early 1945. Sir John Dill died in Washington, D.C., in November 1944 and was replaced both as Chief of the British Joint Staff Mission and as a member of the Combined Policy Committee by Field Marshal Sir Henry Maitland Wilson.[74] When cooperation resumed after the Quebec agreement, the Americans' progress and expenditures amazed the British. The United States had already spent more than $1 billion ($13 billion today, equivalent to 20 battleships commissioned at the time), while in 1943, the United Kingdom had spent about £0.5 million ($21 million today). Chadwick thus pressed for British involvement in the Manhattan Project to the fullest extent and abandoned any hopes of an independent British project during the war.[68] With Churchill's backing, he attempted to ensure that every request from Groves for assistance was honored.[75] The British Mission that arrived in the United States in December 1943 included Niels Bohr, Otto Frisch, Klaus Fuchs, Rudolf Peierls, and Ernest Titterton.[76] More scientists arrived in early 1944. While those assigned to gaseous diffusion left by the fall of 1944, the 35 working under Oliphant with Lawrence at Berkeley were assigned to existing laboratory groups and most stayed until the end of the war. The 19 sent to Los Alamos also joined existing groups, primarily related to implosion and bomb assembly, but not the plutonium-related ones.[68] Part of the Quebec Agreement specified that nuclear weapons would not be used against another country without the mutual consent of the US and UK. In June 1945, Wilson agreed that the use of nuclear weapons against Japan would be recorded as a decision of the Combined Policy Committee.[77] The Combined Policy Committee created the Combined Development Trust in June 1944, with Groves as its chairman, to procure uranium and thorium ores on international markets. The Belgian Congo and Canada held much of the world's uranium outside Eastern Europe, and the Belgian government in exile was in London. Britain agreed to give the United States most of the Belgian ore, as it could not use most of the supply without restricted American research.[78] In 1944, the Trust purchased 3,440,000 pounds (1,560,000 kg) of uranium oxide ore from companies operating mines in the Belgian Congo. In order to avoid briefing US Secretary of the Treasury Henry Morgenthau Jr. on the project, a special account not subject to the usual auditing and controls was used to hold Trust monies. Between 1944 and the time he resigned from the Trust in 1947, Groves deposited a total of $37.5 million into the Trust's account.[79] Groves appreciated the early British atomic research and the British scientists' contributions to the Manhattan Project, but stated that the United States would have succeeded without them.[68] He also said that Churchill was "the best friend the atomic bomb project had [as] he kept Roosevelt's interest up ... He just stirred him up all the time by telling him how important he thought the project was."[58] The British wartime participation was crucial to the success of the United Kingdom's independent nuclear weapons program after the war when the McMahon Act of 1946 temporarily ended American nuclear cooperation.[68] Project sites Map of the United States and southern Canada with major project sites marked A selection of US and Canadian sites important to the Manhattan Project. Click on the location for more information. Oak Ridge Main article: Clinton Engineer Works Workers, mostly women, pour out of a cluster of buildings. A billboard exhorts them to "Make C.E.W. COUNT continue to protect project information!" Shift change at the Y-12 uranium enrichment facility at the Clinton Engineer Works in Oak Ridge, Tennessee, on 11 August 1945. By May 1945, 82,000 people were employed at the Clinton Engineer Works.[80] Photograph by the Manhattan District photographer Ed Westcott. The day after he took over the project, Groves took a train to Tennessee with Colonel Marshall to inspect the proposed site there, and Groves was impressed.[81][82] On 29 September 1942, United States Under Secretary of War Robert P. Patterson authorized the Corps of Engineers to acquire 56,000 acres (23,000 ha) of land by eminent domain at a cost of $3.5 million. An additional 3,000 acres (1,200 ha) was subsequently acquired. About 1,000 families were affected by the condemnation order, which came into effect on 7 October.[83] Protests, legal appeals, and a 1943 Congressional inquiry were to no avail.[84] By mid-November U.S. Marshals were tacking notices to vacate on farmhouse doors, and construction contractors were moving in.[85] Some families were given two weeks' notice to vacate farms that had been their homes for generations;[86] others had settled there after being evicted to make way for the Great Smoky Mountains National Park in the 1920s or the Norris Dam in the 1930s.[84] The ultimate cost of land acquisition in the area, which was not completed until March 1945, was only about $2.6 million, which worked out to around $47 an acre.[87] When presented with Public Proclamation Number Two, which declared Oak Ridge a total exclusion area that no one could enter without military permission, the Governor of Tennessee, Prentice Cooper, angrily tore it up.[88] Initially known as the Kingston Demolition Range, the site was officially renamed the Clinton Engineer Works (CEW) in early 1943.[89] While Stone & Webster concentrated on the production facilities, the architectural and engineering firm Skidmore, Owings & Merrill designed and built a residential community for 13,000. The community was located on the slopes of Black Oak Ridge, from which the new town of Oak Ridge got its name.[90] The Army presence at Oak Ridge increased in August 1943 when Nichols replaced Marshall as head of the Manhattan Engineer District. One of his first tasks was to move the district headquarters to Oak Ridge although the name of the district did not change.[91] In September 1943 the administration of community facilities was outsourced to Turner Construction Company through a subsidiary, the Roane-Anderson Company (for Roane and Anderson Counties, in which Oak Ridge was located).[92] Chemical engineers, including William J. (Jenkins) Wilcox Jr. and Warren Fuchs, were part of "frantic efforts" to make 10% to 12% enriched uranium 235, known as the code name "tuballoy tetroxide", with tight security and fast approvals for supplies and materials.[93] The population of Oak Ridge soon expanded well beyond the initial plans, and peaked at 75,000 in May 1945, by which time 82,000 people were employed at the Clinton Engineer Works,[80] and 10,000 by Roane-Anderson.[92] Fine-arts photographer, Josephine Herrick, and her colleague, Mary Steers, helped document the work at Oak Ridge.[94] Los Alamos Main article: Project Y The idea of locating Project Y at Oak Ridge was considered, but in the end it was decided that it should be in a remote location. On Oppenheimer's recommendation, the search for a suitable site was narrowed to the vicinity of Albuquerque, New Mexico, where Oppenheimer owned a ranch. In October 1942, Major John H. Dudley of the Manhattan District was sent to survey the area. He recommended a site near Jemez Springs, New Mexico.[95] On 16 November, Oppenheimer, Groves, Dudley and others toured the site. Oppenheimer feared that the high cliffs surrounding the site would make his people feel claustrophobic, while the engineers were concerned with the possibility of flooding. The party then moved on to the vicinity of the Los Alamos Ranch School. Oppenheimer was impressed and expressed a strong preference for the site, citing its natural beauty and views of the Sangre de Cristo Mountains, which, it was hoped, would inspire those who would work on the project.[96][97] The engineers were concerned about the poor access road, and whether the water supply would be adequate, but otherwise felt that it was ideal.[98] A group of men in shirtsleeves sitting on folding chairs Physicists at a Manhattan District-sponsored colloquium at the Los Alamos Laboratory on the Super in April 1946. In the front row are Norris Bradbury, John Manley, Enrico Fermi and J. (Jerome) M. B. Kellogg. Robert Oppenheimer, in dark coat, is behind Manley; to Oppenheimer's left is Richard Feynman. The Army officer on the left is Colonel Oliver Haywood. Patterson approved the acquisition of the site on 25 November 1942, authorizing $440,000 for the purchase of the site of 54,000 acres (22,000 ha), all but 8,900 acres (3,600 ha) of which were already owned by the Federal Government.[99] Secretary of Agriculture Claude R. Wickard granted use of some 45,100 acres (18,300 ha) of United States Forest Service land to the War Department "for so long as the military necessity continues".[100] The need for land, for a new road, and later for a right of way for a 25-mile (40 km) power line, eventually brought wartime land purchases to 45,737 acres (18,509.1 ha), but only $414,971 was spent.[99] Construction was contracted to the M. M. Sundt Company of Tucson, Arizona, with Willard C. Kruger and Associates of Santa Fe, New Mexico, as architect and engineer. Work commenced in December 1942. Groves initially allocated $300,000 for construction, three times Oppenheimer's estimate, with a planned completion date of 15 March 1943. It soon became clear that the scope of Project Y was greater than expected, and by the time Sundt finished on 30 November 1943, over $7 million had been spent.[101] Map of Los Alamos site, New Mexico, 1943–45 Because it was secret, Los Alamos was referred to as "Site Y" or "the Hill".[102] Birth certificates of babies born in Los Alamos during the war listed their place of birth as PO Box 1663 in Santa Fe.[103] Initially Los Alamos was to have been a military laboratory with Oppenheimer and other researchers commissioned into the Army. Oppenheimer went so far as to order himself a lieutenant colonel's uniform, but two key physicists, Robert Bacher and Isidor Rabi, balked at the idea. Conant, Groves and Oppenheimer then devised a compromise whereby the laboratory was operated by the University of California under contract to the War Department.[104] Chicago Main article: Metallurgical Laboratory An Army-OSRD council on 25 June 1942 decided to build a pilot plant for plutonium production in Red Gate Woods southwest of Chicago. In July, Nichols arranged for a lease of 1,025 acres (415 ha) from the Cook County Forest Preserve District, and Captain James F. Grafton (1908-1969) was appointed Chicago area engineer. It soon became apparent that the scale of operations was too great for the area, and it was decided to build the plant at Oak Ridge, and keep a research and testing facility in Chicago.[105][106] Delays in establishing the plant in Red Gate Woods led Compton to authorize the Metallurgical Laboratory to construct the first nuclear reactor beneath the bleachers of Stagg Field at the University of Chicago. The reactor required an enormous amount of graphite blocks and uranium pellets. At the time, there was a limited source of pure uranium. Frank Spedding of Iowa State University was able to produce only two short tons of pure uranium. Additional three short tons of uranium metal was supplied by Westinghouse Lamp Plant which was produced in a rush with makeshift process. A large square balloon was constructed by Goodyear Tire to encase the reactor.[107][108] On 2 December 1942, a team led by Enrico Fermi initiated the first artificial[note 4] self-sustaining nuclear chain reaction in an experimental reactor known as Chicago Pile-1.[110] The point at which a reaction becomes self-sustaining became known as "going critical". Compton reported the success to Conant in Washington, D.C., by a coded phone call, saying, "The Italian navigator [Fermi] has just landed in the new world."[111][note 5] In January 1943, Grafton's successor, Major Arthur V. Peterson, ordered Chicago Pile-1 dismantled and reassembled at Red Gate Woods, as he regarded the operation of a reactor as too hazardous for a densely populated area.[112] At the Argonne site, Chicago Pile-3, the first heavy water reactor, went critical on 15 May 1944.[113][114] After the war, the operations that remained at Red Gate moved to the new site of the Argonne National Laboratory about 6 miles (9.7 km) away.[106] Hanford Main article: Hanford Engineer Works By December 1942 there were concerns that even Oak Ridge was too close to a major population center (Knoxville) in the unlikely event of a major nuclear accident. Groves recruited DuPont in November 1942 to be the prime contractor for the construction of the plutonium production complex. DuPont was offered a standard cost plus fixed-fee contract, but the President of the company, Walter S. Carpenter, Jr., wanted no profit of any kind, and asked for the proposed contract to be amended to explicitly exclude the company from acquiring any patent rights. This was accepted, but for legal reasons a nominal fee of one dollar was agreed upon. After the war, DuPont asked to be released from the contract early, and had to return 33 cents.[115] A large crowd of sullen looking workmen at a counter where two women are writing. Some of the workmen are wearing identify photographs of themselves on their hats. Hanford workers collect their paychecks at the Union office. DuPont recommended that the site be located far from the existing uranium production facility at Oak Ridge.[116] In December 1942, Groves dispatched Colonel Franklin Matthias and DuPont engineers to scout potential sites. Matthias reported that Hanford Site near Richland, Washington, was "ideal in virtually all respects". It was isolated and near the Columbia River, which could supply sufficient water to cool the reactors that would produce the plutonium. Groves visited the site in January and established the Hanford Engineer Works (HEW), codenamed "Site W".[117] Under Secretary Patterson gave his approval on 9 February, allocating $5 million for the acquisition of 430,000 acres (170,000 ha) of land in the area. The federal government relocated some 1,500 residents of White Bluffs and Hanford, and nearby settlements, as well as the Wanapum and other tribes using the area. A dispute arose with farmers over compensation for crops, which had already been planted before the land was acquired. Where schedules allowed, the Army allowed the crops to be harvested, but this was not always possible.[117] The land acquisition process dragged on and was not completed before the end of the Manhattan Project in December 1946.[118] The dispute did not delay work. Although progress on the reactor design at Metallurgical Laboratory and DuPont was not sufficiently advanced to accurately predict the scope of the project, a start was made in April 1943 on facilities for an estimated 25,000 workers, half of whom were expected to live on-site. By July 1944, some 1,200 buildings had been erected and nearly 51,000 people were living in the construction camp. As area engineer, Matthias exercised overall control of the site.[119] At its peak, the construction camp was the third most populous town in Washington state.[120] Hanford operated a fleet of over 900 buses, more than the city of Chicago.[121] Like Los Alamos and Oak Ridge, Richland was a gated community with restricted access, but it looked more like a typical wartime American boomtown: the military profile was lower, and physical security elements like high fences, towers, and guard dogs were less evident.[122] Canadian sites Main article: Montreal Laboratory British Columbia Cominco had produced electrolytic hydrogen at Trail, British Columbia, since 1930. Urey suggested in 1941 that it could produce heavy water. To the existing $10 million plant consisting of 3,215 cells consuming 75 MW of hydroelectric power, secondary electrolysis cells were added to increase the deuterium concentration in the water from 2.3% to 99.8%. For this process, Hugh Taylor of Princeton developed a platinum-on-carbon catalyst for the first three stages while Urey developed a nickel-chromia one for the fourth stage tower. The final cost was $2.8 million. The Canadian Government did not officially learn of the project until August 1942. Trail's heavy water production started in January 1944 and continued until 1956. Heavy water from Trail was used for Chicago Pile 3, the first reactor using heavy water and natural uranium, which went critical on 15 May 1944.[123] Ontario The Chalk River, Ontario, site was established to rehouse the Allied effort at the Montreal Laboratory away from an urban area. A new community was built at Deep River, Ontario, to provide residences and facilities for the team members. The site was chosen for its proximity to the industrial manufacturing area of Ontario and Quebec, and proximity to a rail head adjacent to a large military base, Camp Petawawa. Located on the Ottawa River, it had access to abundant water. The first director of the new laboratory was Hans von Halban. He was replaced by John Cockcroft in May 1944, who in turn was succeeded by Bennett Lewis in September 1946. A pilot reactor known as ZEEP (zero-energy experimental pile) became the first Canadian reactor, and the first to be completed outside the United States, when it went critical in September 1945, ZEEP remained in use by researchers until 1970.[124] A larger 10 MW NRX reactor, which was designed during the war, was completed and went critical in July 1947.[123] Northwest Territories The Eldorado Mine at Port Radium was a source of uranium ore.[125] Heavy water sites Main article: P-9 Project Although DuPont's preferred designs for the nuclear reactors were helium cooled and used graphite as a moderator, DuPont still expressed an interest in using heavy water as a backup, in case the graphite reactor design proved infeasible for some reason. For this purpose, it was estimated that 3 short tons (2.7 t) of heavy water would be required per month. The P-9 Project was the government's code name for the heavy water production program. As the plant at Trail, which was then under construction, could produce 0.5 short tons (0.45 t) per month, additional capacity was required. Groves therefore authorized DuPont to establish heavy water facilities at the Morgantown Ordnance Works, near Morgantown, West Virginia; at the Wabash River Ordnance Works, near Dana and Newport, Indiana; and at the Alabama Ordnance Works, near Childersburg and Sylacauga, Alabama. Although known as Ordnance Works and paid for under Ordnance Department contracts, they were built and operated by the Army Corps of Engineers. The American plants used a process different from Trail's; heavy water was extracted by distillation, taking advantage of the slightly higher boiling point of heavy water.[126][127] Uranium Ore The majority of the uranium used in the Manhattan Project came from the Shinkolobwe mine in Belgian Congo. The key raw material for the project was uranium, which was used as fuel for the reactors, as feed that was transformed into plutonium, and, in its enriched form, in the atomic bomb itself. There were four known major deposits of uranium in 1940: in Colorado, in northern Canada, in Joachimsthal in Czechoslovakia, and in the Belgian Congo.[128] All but Joachimstal were in Allied hands. A November 1942 survey determined that sufficient quantities of uranium were available to satisfy the project's requirements.[129] Nichols arranged with the State Department for export controls to be placed on uranium oxide and negotiated for the purchase of 1,200 short tons (1,100 t) of uranium ore from the Belgian Congo that was being stored in a warehouse on Staten Island and the remaining stocks of mined ore stored in the Congo. He negotiated with Eldorado Gold Mines for the purchase of ore from its refinery in Port Hope, Ontario, and its shipment in 100-ton lots. The Canadian government subsequently bought up the company's stock until it acquired a controlling interest.[130] While these purchases assured a sufficient supply to meet wartime needs, the American and British leaders concluded that it was in their countries' interest to gain control of as much of the world's uranium deposits as possible. The richest source of ore was the Shinkolobwe mine in the Belgian Congo, but it was flooded and closed. Nichols unsuccessfully attempted to negotiate its reopening and the sale of the entire future output to the United States with Edgar Sengier, the director of the company that owned the mine, the Union Minière du Haut-Katanga.[131] The matter was then taken up by the Combined Policy Committee. As 30 percent of Union Minière's stock was controlled by British interests, the British took the lead in negotiations. Sir John Anderson and Ambassador John Winant hammered out a deal with Sengier and the Belgian government in May 1944 for the mine to be reopened and 1,720 short tons (1,560 t) of ore to be purchased at $1.45 a pound.[132] To avoid dependence on the British and Canadians for ore, Groves also arranged for the purchase of US Vanadium Corporation's stockpile in Uravan, Colorado. Uranium mining in Colorado yielded about 800 short tons (730 t) of ore.[133] Mallinckrodt Incorporated in St. Louis, Missouri, took the raw ore and dissolved it in nitric acid to produce uranyl nitrate. Ether was then added in a liquid–liquid extraction process to separate the impurities from the uranyl nitrate. This was then heated to form uranium trioxide, which was reduced to highly pure uranium dioxide.[134] By July 1942, Mallinckrodt was producing a ton of highly pure oxide a day, but turning this into uranium metal initially proved more difficult for contractors Westinghouse and Metal Hydrides.[135] Production was too slow and quality was unacceptably low. A special branch of the Metallurgical Laboratory was established at Iowa State College in Ames, Iowa, under Frank Spedding to investigate alternatives. This became known as the Ames Project, and its Ames process became available in 1943.[136] Uranium refining at Ames A "bomb" (pressure vessel) containing uranium halide and sacrificial metal, probably magnesium, being lowered into a furnace A "bomb" (pressure vessel) containing uranium halide and sacrificial metal, probably magnesium, being lowered into a furnace   After the reaction, the interior of a bomb coated with remnant slag After the reaction, the interior of a bomb coated with remnant slag   A uranium metal "biscuit" from the reduction reaction A uranium metal "biscuit" from the reduction reaction Isotope separation Natural uranium consists of 99.3% uranium-238 and 0.7% uranium-235, but only the latter is fissile. The chemically identical uranium-235 has to be physically separated from the more plentiful isotope. Various methods were considered for uranium enrichment, most of which was carried out at Oak Ridge.[137] The most obvious technology, the centrifuge, failed, but electromagnetic separation, gaseous diffusion, and thermal diffusion technologies were all successful and contributed to the project. In February 1943, Groves came up with the idea of using the output of some plants as the input for others.[138] Contour map of the Oak Ridge area. There is a river to the south, while the township is in the north. Oak Ridge hosted several uranium separation technologies. The Y-12 electromagnetic separation plant is in the upper right. The K-25 and K-27 gaseous diffusion plants are in the lower left, near the S-50 thermal diffusion plant. The X-10 was for plutonium production. Centrifuges The centrifuge process was regarded as the only promising separation method in April 1942.[139] Jesse Beams had developed such a process at the University of Virginia during the 1930s, but had encountered technical difficulties. The process required high rotational speeds, but at certain speeds harmonic vibrations developed that threatened to tear the machinery apart. It was therefore necessary to accelerate quickly through these speeds. In 1941 he began working with uranium hexafluoride, the only known gaseous compound of uranium, and was able to separate uranium-235. At Columbia, Urey had Karl P. Cohen investigate the process, and he produced a body of mathematical theory making it possible to design a centrifugal separation unit, which Westinghouse undertook to construct.[140] Scaling this up to a production plant presented a formidable technical challenge. Urey and Cohen estimated that producing a kilogram (2.2 lb) of uranium-235 per day would require up to 50,000 centrifuges with 1-meter (3 ft 3 in) rotors, or 10,000 centrifuges with 4-meter (13 ft) rotors, assuming that 4-meter rotors could be built. The prospect of keeping so many rotors operating continuously at high speed appeared daunting,[141] and when Beams ran his experimental apparatus, he obtained only 60% of the predicted yield, indicating that more centrifuges would be required. Beams, Urey and Cohen then began work on a series of improvements which promised to increase the efficiency of the process. However, frequent failures of motors, shafts and bearings at high speeds delayed work on the pilot plant.[142] In November 1942 the centrifuge process was abandoned by the Military Policy Committee following a recommendation by Conant, Nichols and August C. Klein of Stone & Webster.[143] Although the centrifuge method was abandoned by the Manhattan Project, research into it advanced significantly after the war with the introduction of the Zippe-type centrifuge, which was developed in the Soviet Union by Soviet and captured German engineers.[144] It eventually became the preferred method of Uranium isotope separation, being far more economical than the other separation methods used during World War II.[145] Electromagnetic separation Main article: Y-12 Project Electromagnetic isotope separation was developed by Lawrence at the University of California Radiation Laboratory. This method employed devices known as calutrons, a hybrid of the standard laboratory mass spectrometer and the cyclotron magnet. The name was derived from the words California, university and cyclotron.[146] In the electromagnetic process, a magnetic field deflected charged particles according to mass.[147] The process was neither scientifically elegant nor industrially efficient.[148] Compared with a gaseous diffusion plant or a nuclear reactor, an electromagnetic separation plant would consume more scarce materials, require more manpower to operate, and cost more to build. Nonetheless, the process was approved because it was based on proven technology and therefore represented less risk. Moreover, it could be built in stages, and rapidly reach industrial capacity.[146] A large oval-shaped structure Alpha I racetrack at Y-12 Marshall and Nichols discovered that the electromagnetic isotope separation process would require 5,000 short tons (4,500 tonnes) of copper, which was in desperately short supply. However, silver could be substituted, in an 11:10 ratio. On 3 August 1942, Nichols met with Under Secretary of the Treasury Daniel W. Bell and asked for the transfer of 6,000 tons of silver bullion from the West Point Bullion Depository. "Young man," Bell told him, "you may think of silver in tons but the Treasury will always think of silver in troy ounces!"[149] Ultimately 14,700 short tons (13,300 tonnes; 430,000,000 troy ounces) were used.[150] The 1,000-troy-ounce (31 kg) silver bars were cast into cylindrical billets and taken to Phelps Dodge in Bayway, New Jersey, where they were extruded into strips 0.625 inches (15.9 mm) thick, 3 inches (76 mm) wide and 40 feet (12 m) long. These were wound onto magnetic coils by Allis-Chalmers in Milwaukee, Wisconsin. After the war, all the machinery was dismantled and cleaned and the floorboards beneath the machinery were ripped up and burned to recover minute amounts of silver. In the end, only 1/3,600,000th was lost.[150][151] The last silver was returned in May 1970.[152] Responsibility for the design and construction of the electromagnetic separation plant, which came to be called Y-12, was assigned to Stone & Webster by the S-1 Committee in June 1942. The design called for five first-stage processing units, known as Alpha racetracks, and two units for final processing, known as Beta racetracks. In September 1943 Groves authorized construction of four more racetracks, known as Alpha II. Construction began in February 1943.[153] When the plant was started up for testing on schedule in October, the 14-ton vacuum tanks crept out of alignment because of the power of the magnets, and had to be fastened more securely. A more serious problem arose when the magnetic coils started shorting out. In December Groves ordered a magnet to be broken open, and handfuls of rust were found inside. Groves then ordered the racetracks to be torn down and the magnets sent back to the factory to be cleaned. A pickling plant was established on-site to clean the pipes and fittings.[148] The second Alpha I was not operational until the end of January 1944, the first Beta and first and third Alpha I's came online in March, and the fourth Alpha I was operational in April. The four Alpha II racetracks were completed between July and October 1944.[154] A long corridor with many consoles with dials and switches, attended by women seated on high stools Calutron Girls were young women who monitored calutron control panels at Y-12. Gladys Owens, seated in the foreground, was unaware of what she had been involved in.[155] Tennessee Eastman was contracted to manage Y-12 on the usual cost plus fixed-fee basis, with a fee of $22,500 per month plus $7,500 per racetrack for the first seven racetracks and $4,000 per additional racetrack.[156] The calutrons were initially operated by scientists from Berkeley to remove bugs and achieve a reasonable operating rate. They were then turned over to trained Tennessee Eastman operators who had only a high school education. Nichols compared unit production data, and pointed out to Lawrence that the young "hillbilly" girl operators, known as Calutron Girls, were outperforming his PhDs. They agreed to a production race and Lawrence lost, a morale boost for the Tennessee Eastman workers and supervisors. The girls were "trained like soldiers not to reason why", while "the scientists could not refrain from time-consuming investigation of the cause of even minor fluctuations of the dials."[157] Y-12 initially enriched the uranium-235 content to between 13% and 15%, and shipped the first few hundred grams of this to Los Alamos in March 1944. Only 1 part in 5,825 of the uranium feed emerged as final product. Much of the rest was splattered over equipment in the process. Strenuous recovery efforts helped raise production to 10% of the uranium-235 feed by January 1945. In February the Alpha racetracks began receiving slightly enriched (1.4%) feed from the new S-50 thermal diffusion plant. The next month it received enhanced (5%) feed from the K-25 gaseous diffusion plant. By August K-25 was producing uranium sufficiently enriched to feed directly into the Beta tracks.[158] Gaseous diffusion Main article: K-25 The most promising but also the most challenging method of isotope separation was gaseous diffusion. Graham's law states that the rate of effusion of a gas is inversely proportional to the square root of its molecular mass, so in a box containing a semi-permeable membrane and a mixture of two gases, the lighter molecules will pass out of the container more rapidly than the heavier molecules. The gas leaving the container is somewhat enriched in the lighter molecules, while the residual gas is somewhat depleted. The idea was that such boxes could be formed into a cascade of pumps and membranes, with each successive stage containing a slightly more enriched mixture. Research into the process was carried out at Columbia University by a group that included Harold Urey, Karl P. Cohen, and John R. Dunning.[159] Oblique aerial view of an enormous U-shaped building Oak Ridge K-25 plant In November 1942 the Military Policy Committee approved the construction of a 600-stage gaseous diffusion plant.[160] On 14 December, M. W. Kellogg accepted an offer to construct the plant, which was codenamed K-25. A cost plus fixed-fee contract was negotiated, eventually totaling $2.5 million. A separate corporate entity called Kellex was created for the project, headed by Percival C. Keith, one of Kellogg's vice presidents.[161] The process faced formidable technical difficulties. The highly corrosive gas uranium hexafluoride would have to be used, as no substitute could be found, and the motors and pumps would have to be vacuum tight and enclosed in inert gas. The biggest problem was the design of the barrier, which would have to be strong, porous and resistant to corrosion by uranium hexafluoride. The best choice for this seemed to be nickel. Edward Adler and Edward Norris created a mesh barrier from electroplated nickel. A six-stage pilot plant was built at Columbia to test the process, but the Norris-Adler prototype proved to be too brittle. A rival barrier was developed from powdered nickel by Kellex, the Bell Telephone Laboratories and the Bakelite Corporation. In January 1944, Groves ordered the Kellex barrier into production.[162][163] Kellex's design for K-25 called for a four-story 0.5-mile (0.80 km) long U-shaped structure containing 54 contiguous buildings. These were divided into nine sections. Within these were cells of six stages. The cells could be operated independently, or consecutively within a section. Similarly, the sections could be operated separately or as part of a single cascade. A survey party began construction by marking out the 500-acre (2.0 km2) site in May 1943. Work on the main building began in October 1943, and the six-stage pilot plant was ready for operation on 17 April 1944. In 1945 Groves canceled the upper stages of the plant, directing Kellex to instead design and build a 540-stage side feed unit, which became known as K-27. Kellex transferred the last unit to the operating contractor, Union Carbide and Carbon, on 11 September 1945. The total cost, including the K-27 plant completed after the war, came to $480 million.[164] The production plant commenced operation in February 1945, and as cascade after cascade came online, the quality of the product increased. By April 1945, K-25 had attained a 1.1% enrichment and the output of the S-50 thermal diffusion plant began being used as feed. Some product produced the next month reached nearly 7% enrichment. In August, the last of the 2,892 stages commenced operation. K-25 and K-27 achieved their full potential in the early postwar period, when they eclipsed the other production plants and became the prototypes for a new generation of plants.[165] Thermal diffusion Main article: S-50 Project The thermal diffusion process was based on Sydney Chapman and David Enskog's theory, which explained that when a mixed gas passes through a temperature gradient, the heavier one tends to concentrate at the cold end and the lighter one at the warm end. Since hot gases tend to rise and cool ones tend to fall, this can be used as a means of isotope separation. This process was first demonstrated by Klaus Clusius and Gerhard Dickel in Germany in 1938.[166] It was developed by US Navy scientists, but was not one of the enrichment technologies initially selected for use in the Manhattan Project. This was primarily due to doubts about its technical feasibility, but the inter-service rivalry between the Army and Navy also played a part.[167] A factory with three smoking chimneys on a river bend, viewed from above The S-50 plant is the dark building to the upper left behind the Oak Ridge powerhouse (with smoke stacks). The Naval Research Laboratory continued the research under Philip Abelson's direction, but there was little contact with the Manhattan Project until April 1944, when Captain William S. Parsons, the naval officer in charge of ordnance development at Los Alamos, brought Oppenheimer news of encouraging progress in the Navy's experiments on thermal diffusion. Oppenheimer wrote to Groves suggesting that the output of a thermal diffusion plant could be fed into Y-12. Groves set up a committee consisting of Warren K. Lewis, Eger Murphree and Richard Tolman to investigate the idea, and they estimated that a thermal diffusion plant costing $3.5 million could enrich 50 kilograms (110 lb) of uranium per week to nearly 0.9% uranium-235. Groves approved its construction on 24 June 1944.[168] Groves contracted with the H. K. Ferguson Company of Cleveland, Ohio, to build the thermal diffusion plant, which was designated S-50. Groves's advisers, Karl Cohen and W. I. Thompson from Standard Oil,[169] estimated that it would take six months to build. Groves gave Ferguson just four. Plans called for the installation of 2,142 48-foot-tall (15 m) diffusion columns arranged in 21 racks. Inside each column were three concentric tubes. Steam, obtained from the nearby K-25 powerhouse at a pressure of 100 pounds per square inch (690 kPa) and temperature of 545 °F (285 °C), flowed downward through the innermost 1.25-inch (32 mm) nickel pipe, while water at 155 °F (68 °C) flowed upward through the outermost iron pipe. The uranium hexafluoride flowed in the middle copper pipe, and isotope separation of the uranium occurred between the nickel and copper pipes.[170] Work commenced on 9 July 1944, and S-50 began partial operation in September. Ferguson operated the plant through a subsidiary known as Fercleve. The plant produced just 10.5 pounds (4.8 kg) of 0.852% uranium-235 in October. Leaks limited production and forced shutdowns over the next few months, but in June 1945 it produced 12,730 pounds (5,770 kg).[171] By March 1945, all 21 production racks were operating. Initially the output of S-50 was fed into Y-12, but starting in March 1945 all three enrichment processes were run in series. S-50 became the first stage, enriching from 0.71% to 0.89%. This material was fed into the gaseous diffusion process in the K-25 plant, which produced a product enriched to about 23%. This was, in turn, fed into Y-12,[172] which boosted it to about 89%, sufficient for nuclear weapons. About 50 kilograms (110 lb) of uranium enriched to 89% uranium-235 was delivered to Los Alamos by July 1945. The entire 50 kg, along with some 50%-enriched, averaging out to about 85% enriched, were used in the first Little Boy.[173] Plutonium The second line of development pursued by the Manhattan Project used the fissile element plutonium. Although small amounts of plutonium exist in nature, the best way to obtain large quantities of the element is in a nuclear reactor, in which natural uranium is bombarded by neutrons. The uranium-238 is transmuted into uranium-239, which rapidly decays, first into neptunium-239 and then into plutonium-239.[174] Only a small amount of the uranium-238 will be transformed, so the plutonium must be chemically separated from the remaining uranium, from any initial impurities, and from fission products.[174] X-10 Graphite Reactor Main article: X-10 Graphite Reactor Two workmen on a movable platform similar to that used by window washers, stick a rod into one of many small holes in the wall in front of them. Workers load uranium slugs into the X-10 Graphite Reactor. In March 1943, DuPont began construction of a plutonium plant on a 112-acre (0.5 km2) site at Oak Ridge. Intended as a pilot plant for the larger production facilities at Hanford, it included the air-cooled X-10 Graphite Reactor, a chemical separation plant, and support facilities. Because of the subsequent decision to construct water-cooled reactors at Hanford, only the chemical separation plant operated as a true pilot.[175] The X-10 Graphite Reactor consisted of a huge block of graphite, 24 feet (7.3 m) long on each side, weighing around 1,500 short tons (1,400 t), surrounded by 7 feet (2.1 m) of high-density concrete as a radiation shield.[175] The greatest difficulty was encountered with the uranium slugs produced by Mallinckrodt and Metal Hydrides. These somehow had to be coated in aluminum to avoid corrosion and the escape of fission products into the cooling system. The Grasselli Chemical Company attempted to develop a hot dipping process without success. Meanwhile, Alcoa tried canning. A new process for flux-less welding was developed, and 97% of the cans passed a standard vacuum test, but high temperature tests indicated a failure rate of more than 50%. Nonetheless, production began in June 1943. The Metallurgical Laboratory eventually developed an improved welding technique with the help of General Electric, which was incorporated into the production process in October 1943.[176] Watched by Fermi and Compton, the X-10 Graphite Reactor went critical on 4 November 1943 with about 30 short tons (27 t) of uranium. A week later the load was increased to 36 short tons (33 t), raising its power generation to 500 kW, and by the end of the month the first 500 mg of plutonium was created.[177] Modifications over time raised the power to 4,000 kW in July 1944. X-10 operated as a production plant until January 1945, when it was turned over to research activities.[178] Hanford reactors Main article: Hanford Engineer Works Although an air-cooled design was chosen for the reactor at Oak Ridge to facilitate rapid construction, it was recognized that this would be impractical for the much larger production reactors. Initial designs by the Metallurgical Laboratory and DuPont used helium for cooling, before they determined that a water-cooled reactor would be simpler, cheaper and quicker to build.[179] The design did not become available until 4 October 1943; in the meantime, Matthias concentrated on improving the Hanford Site by erecting accommodations, improving the roads, building a railway switch line, and upgrading the electricity, water and telephone lines.[180] An aerial view of the Hanford B-Reactor site from June 1944. At center is the reactor building. Small trucks dot the landscape and give a sense of scale. Two large water towers loom above the plant. Aerial view of Hanford B-Reactor site, June 1944 As at Oak Ridge, the most difficulty was encountered while canning the uranium slugs, which commenced at Hanford in March 1944. They were pickled to remove dirt and impurities, dipped in molten bronze, tin, and aluminum-silicon alloy, canned using hydraulic presses, and then capped using arc welding under an argon atmosphere. Finally, they were subjected to a series of tests to detect holes or faulty welds. Disappointingly, most canned slugs initially failed the tests, resulting in an output of only a handful of canned slugs per day. But steady progress was made and by June 1944 production increased to the point where it appeared that enough canned slugs would be available to start Reactor B on schedule in August 1944.[181] Work began on Reactor B, the first of six planned 250 MW reactors, on 10 October 1943.[182] The reactor complexes were given letter designations A through F, with B, D and F sites chosen to be developed first, as this maximised the distance between the reactors. They would be the only ones constructed during the Manhattan Project.[183] Some 390 short tons (350 t) of steel, 17,400 cubic yards (13,300 m3) of concrete, 50,000 concrete blocks and 71,000 concrete bricks were used to construct the 120-foot (37 m) high building. Construction of the reactor itself commenced in February 1944.[184] Watched by Compton, Matthias, DuPont's Crawford Greenewalt, Leona Woods and Fermi, who inserted the first slug, the reactor was powered up beginning on 13 September 1944. Over the next few days, 838 tubes were loaded and the reactor went critical. Shortly after midnight on 27 September, the operators began to withdraw the control rods to initiate production. At first all appeared well but around 03:00 the power level started to drop and by 06:30 the reactor had shut down completely. The cooling water was investigated to see if there was a leak or contamination. The next day the reactor started up again, only to shut down once more.[185][186] Fermi contacted Chien-Shiung Wu, who identified the cause of the problem as neutron poisoning from xenon-135, which has a half-life of 9.2 hours.[187] Fermi, Woods, Donald J. Hughes and John Archibald Wheeler then calculated the nuclear cross section of xenon-135, which turned out to be 30,000 times that of uranium.[188] DuPont engineer George Graves had deviated from the Metallurgical Laboratory's original design in which the reactor had 1,500 tubes arranged in a circle, and had added an additional 504 tubes to fill in the corners. The scientists had originally considered this overengineering a waste of time and money, but Fermi realized that by loading all 2,004 tubes, the reactor could reach the required power level and efficiently produce plutonium.[189] Reactor D was started on 17 December 1944 and Reactor F on 25 February 1945.[190] Separation process A contour map showing the fork of the Columbia and Yakima rivers and the boundary of the land, with seven small red squares marked on it Map of the Hanford Site. Railroads flank the plants to the north and south. Reactors are the three northernmost red squares, along the Columbia River. The separation plants are the lower two red squares from the grouping south of the reactors. The bottom red square is the 300 area. Meanwhile, the chemists considered the problem of how plutonium could be separated from uranium when its chemical properties were not known. Working with the minute quantities of plutonium available at the Metallurgical Laboratory in 1942, a team under Charles M. Cooper developed a lanthanum fluoride process for separating uranium and plutonium, which was chosen for the pilot separation plant. A second separation process, the bismuth phosphate process, was subsequently developed by Seaborg and Stanly G. Thomson.[191] This process worked by toggling plutonium between its +4 and +6 oxidation states in solutions of bismuth phosphate. In the former state, the plutonium was precipitated; in the latter, it stayed in solution and the other products were precipitated.[192] Greenewalt favored the bismuth phosphate process due to the corrosive nature of lanthanum fluoride, and it was selected for the Hanford separation plants.[193] Once X-10 began producing plutonium, the pilot separation plant was put to the test. The first batch was processed at 40% efficiency but over the next few months this was raised to 90%.[178] At Hanford, top priority was initially given to the installations in the 300 area. This contained buildings for testing materials, preparing uranium, and assembling and calibrating instrumentation. One of the buildings housed the canning equipment for the uranium slugs, while another contained a small test reactor. Notwithstanding the high priority allocated to it, work on the 300 area fell behind schedule due to the unique and complex nature of the 300 area facilities, and wartime shortages of labor and materials.[194] Early plans called for the construction of two separation plants in each of the areas known as 200-West and 200-East. This was subsequently reduced to two, the T and U plants, in 200-West and one, the B plant, at 200-East.[195] Each separation plant consisted of four buildings: a process cell building or "canyon" (known as 221), a concentration building (224), a purification building (231) and a magazine store (213). The canyons were each 800 feet (240 m) long and 65 feet (20 m) wide. Each consisted of forty 17.7-by-13-by-20-foot (5.4 by 4.0 by 6.1 m) cells.[196] Work began on 221-T and 221-U in January 1944, with the former completed in September and the latter in December. The 221-B building followed in March 1945. Because of the high levels of radioactivity involved, all work in the separation plants had to be conducted by remote control using closed-circuit television, something unheard of in 1943. Maintenance was carried out with the aid of an overhead crane and specially designed tools. The 224 buildings were smaller because they had less material to process, and it was less radioactive. The 224-T and 224-U buildings were completed on 8 October 1944, and 224-B followed on 10 February 1945. The purification methods that were eventually used in 231-W were still unknown when construction commenced on 8 April 1944, but the plant was complete and the methods were selected by the end of the year.[197] On 5 February 1945, Matthias hand-delivered the first shipment of 80 g of 95%-pure plutonium nitrate to a Los Alamos courier in Los Angeles.[190] Weapon design Main article: Project Y Long, tube-like casings. In the background are several ovoid casings and a tow truck. A row of Thin Man casings. Fat Man casings are visible in the background. In 1943, development efforts were directed to a gun-type fission weapon with plutonium called Thin Man. Initial research on the properties of plutonium was done using cyclotron-generated plutonium-239, which was extremely pure, but could only be created in very small amounts. The idea behind the Thin Man design was to fire one subcritical mass of plutonium at another and the collision would create a nuclear explosion.[198] Los Alamos received the first sample of plutonium from the Clinton X-10 reactor in April 1944 and within days Emilio Segrè discovered a problem: the reactor-bred plutonium had a higher concentration of plutonium-240, resulting in up to five times the spontaneous fission rate of cyclotron plutonium.[199] Seaborg had correctly predicted in March 1943 that some of the plutonium-239 would absorb a neutron and become plutonium-240.[200] This made reactor plutonium unsuitable for use in a gun-type weapon. The plutonium-240 would start the chain reaction too quickly, causing a predetonation that would release enough energy to disperse the critical mass with a minimal amount of plutonium reacted (a fizzle). A faster gun was suggested but found to be impractical. The possibility of separating the isotopes was considered and rejected, as plutonium-240 is even harder to separate from plutonium-239 than uranium-235 from uranium-238.[201] Work on an alternative method of bomb design, known as implosion, had begun earlier under the direction of the physicist Seth Neddermeyer. Implosion used explosives to crush a subcritical sphere of fissile material into a smaller and denser form. When the fissile atoms are packed closer together, the rate of neutron capture increases, and the mass becomes a critical mass. The metal needs to travel only a very short distance, so the critical mass is assembled in much less time than it would take with the gun method.[202] Neddermeyer's 1943 and early 1944 investigations into implosion showed promise, but also made it clear that the problem would be much more difficult from a theoretical and engineering perspective than the gun design.[203] In September 1943, John von Neumann, who had experience with shaped charges used in armor-piercing shells, argued that not only would implosion reduce the danger of predetonation and fizzle, but would make more efficient use of the fissionable material.[204] He proposed using a spherical configuration instead of the cylindrical one that Neddermeyer was working on.[205] Diagram showing fast explosive, slow explosive, uranium tamper, plutonium core and neutron initiator An implosion-type nuclear bomb By July 1944, Oppenheimer had concluded plutonium could not be used in a gun design, and opted for implosion. The accelerated effort on an implosion design, codenamed Fat Man, began in August 1944 when Oppenheimer implemented a sweeping reorganization of the Los Alamos laboratory to focus on implosion.[206] Two new groups were created at Los Alamos to develop the implosion weapon, X (for explosives) Division headed by explosives expert George Kistiakowsky and G (for gadget) Division under Robert Bacher.[207][208] The new design that von Neumann and T (for theoretical) Division, most notably Rudolf Peierls, had devised used explosive lenses to focus the explosion onto a spherical shape using a combination of both slow and fast high explosives.[209] The design of lenses that detonated with the proper shape and velocity turned out to be slow, difficult and frustrating.[209] Various explosives were tested before settling on composition B as the fast explosive and baratol as the slow explosive.[210] The final design resembled a soccer ball, with 20 hexagonal and 12 pentagonal lenses, each weighing about 80 pounds (36 kg). Getting the detonation just right required fast, reliable and safe electrical detonators, of which there were two for each lens for reliability.[211] It was therefore decided to use exploding-bridgewire detonators, a new invention developed at Los Alamos by a group led by Luis Alvarez. A contract for their manufacture was given to Raytheon.[212] To study the behavior of converging shock waves, Robert Serber devised the RaLa Experiment, which used the short-lived radioisotope lanthanum-140, a potent source of gamma radiation. The gamma ray source was placed in the center of a metal sphere surrounded by the explosive lenses, which in turn were inside in an ionization chamber. This allowed the taking of an X-ray movie of the implosion. The lenses were designed primarily using this series of tests.[213] In his history of the Los Alamos project, David Hawkins wrote: "RaLa became the most important single experiment affecting the final bomb design".[214] Within the explosives was the 4.5-inch (110 mm) thick aluminum pusher, which provided a smooth transition from the relatively low density explosive to the next layer, the 3-inch (76 mm) thick tamper of natural uranium. Its main job was to hold the critical mass together as long as possible, but it would also reflect neutrons back into the core. Some part of it might fission as well. To prevent predetonation by an external neutron, the tamper was coated in a thin layer of boron.[211] A polonium-beryllium modulated neutron initiator, known as an "urchin" because its shape resembled a sea urchin,[215] was developed to start the chain reaction at precisely the right moment.[216] This work with the chemistry and metallurgy of radioactive polonium was directed by Charles Allen Thomas of the Monsanto Company and became known as the Dayton Project.[217] Testing required up to 500 curies per month of polonium, which Monsanto was able to deliver.[218] The whole assembly was encased in a duralumin bomb casing to protect it from bullets and flak.[211] A shack surrounded by pine trees. There is snow on the ground. A man and a woman in white lab coats are pulling on a rope, which is attached to a small trolley on a wooden platform. On top of the trolley is a large cylindrical object. Remote handling of a kilocurie source of radiolanthanum for a RaLa Experiment at Los Alamos The ultimate task of the metallurgists was to determine how to cast plutonium into a sphere. The difficulties became apparent when attempts to measure the density of plutonium gave inconsistent results. At first contamination was believed to be the cause, but it was soon determined that there were multiple allotropes of plutonium.[219] The brittle α phase that exists at room temperature changes to the plastic β phase at higher temperatures. Attention then shifted to the even more malleable δ phase that normally exists in the 300 °C to 450 °C range. It was found that this was stable at room temperature when alloyed with aluminum, but aluminum emits neutrons when bombarded with alpha particles, which would exacerbate the pre-ignition problem. The metallurgists then hit upon a plutonium-gallium alloy, which stabilized the δ phase and could be hot pressed into the desired spherical shape. As plutonium was found to corrode readily, the sphere was coated with nickel.[220] The work proved dangerous. By the end of the war, half the experienced chemists and metallurgists had to be removed from work with plutonium when unacceptably high levels of the element appeared in their urine.[221] A minor fire at Los Alamos in January 1945 led to a fear that a fire in the plutonium laboratory might contaminate the whole town, and Groves authorized the construction of a new facility for plutonium chemistry and metallurgy, which became known as the DP-site.[222] The hemispheres for the first plutonium pit (or core) were produced and delivered on 2 July 1945. Three more hemispheres followed on 23 July and were delivered three days later.[223] In contrast to the plutonium Fat Man, the uranium gun-type Little Boy weapon was straightforward if not trivial to design. Overall responsibility for it was assigned to Parsons's Ordnance (O) Division, with the design, development, and technical work at Los Alamos consolidated under Lieutenant Commander Francis Birch's group. The gun-type design now had to work with enriched uranium only, and this allowed the design to be greatly simplified. A high-velocity gun was no longer required, and a simpler weapon was substituted.[224][225] Trinity Main article: Trinity (nuclear test) Because of the complexity of an implosion-style weapon, it was decided that, despite the waste of fissile material, an initial test would be required. Groves approved the test, subject to the active material being recovered. Consideration was therefore given to a controlled fizzle, but Oppenheimer opted instead for a full-scale nuclear test, codenamed "Trinity".[226] Men stand around a large oil-rig type structure. A large round object is being hoisted up. The explosives of "the gadget" were raised to the top of the tower for the final assembly. In March 1944, planning for the test was assigned to Kenneth Bainbridge, a professor of physics at Harvard, working under Kistiakowsky. Bainbridge selected the bombing range near Alamogordo Army Airfield as the site for the test.[227] Bainbridge worked with Captain Samuel P. Davalos on the construction of the Trinity Base Camp and its facilities, which included barracks, warehouses, workshops, an explosive magazine and a commissary.[228] Groves did not relish the prospect of explaining to a Senate committee the loss of a billion dollars worth of plutonium, so a cylindrical containment vessel codenamed "Jumbo" was constructed to recover the active material in the event of a failure. Measuring 25 feet (7.6 m) long and 12 feet (3.7 m) wide, it was fabricated at great expense from 214 short tons (194 t) of iron and steel by Babcock & Wilcox in Barberton, Ohio. Brought in a special railroad car to a siding in Pope, New Mexico, it was transported the last 25 miles (40 km) to the test site on a trailer pulled by two tractors.[229] By the time it arrived, however, confidence in the implosion method was high enough, and the availability of plutonium was sufficient, that Oppenheimer decided not to use it. Instead, it was placed atop a steel tower 800 yards (730 m) from the weapon as a rough measure of how powerful the explosion would be. In the end, Jumbo survived, although its tower did not, adding credence to the belief that Jumbo would have successfully contained a fizzled explosion.[230][231] A pre-test explosion was conducted on 7 May 1945 to calibrate the instruments. A wooden test platform was erected 800 yards (730 m) from Ground Zero and piled with 100 short tons (91 t) of TNT spiked with nuclear fission products in the form of an irradiated uranium slug from Hanford, which was dissolved and poured into tubing inside the explosive. This explosion was observed by Oppenheimer and Groves's new deputy commander, Brigadier General Thomas Farrell. The pre-test produced data that proved vital for the Trinity test.[231][232] The Trinity test of the Manhattan Project was the first detonation of a nuclear weapon. For the actual test, the weapon, nicknamed "the gadget", was hoisted to the top of a 100-foot (30 m) steel tower, as detonation at that height would give a better indication of how the weapon would behave when dropped from a bomber. Detonation in the air maximized the energy applied directly to the target, and generated less nuclear fallout. The gadget was assembled under the supervision of Norris Bradbury at the nearby McDonald Ranch House on 13 July, and precariously winched up the tower the following day.[233] Observers included Bush, Chadwick, Conant, Farrell, Fermi, Groves, Lawrence, Oppenheimer and Tolman. At 05:30 on 16 July 1945 the gadget exploded with an energy equivalent of around 20 kilotons of TNT, leaving a crater of Trinitite (radioactive glass) in the desert 250 feet (76 m) wide. The shock wave was felt over 100 miles (160 km) away, and the mushroom cloud reached 7.5 miles (12.1 km) in height. It was heard as far away as El Paso, Texas, so Groves issued a cover story about an ammunition magazine explosion at Alamogordo Field.[234][235] Oppenheimer later recalled that, while witnessing the explosion, he thought of a verse from the Hindu holy book, the Bhagavad Gita (XI,12): कालोऽस्मि लोकक्षयकृत्प्रवृद्धो लोकान्समाहर्तुमिह प्रवृत्तः। ऋतेऽपि त्वां न भविष्यन्ति सर्वे येऽवस्थिताः प्रत्यनीकेषु योधाः॥११- ३२॥ If the radiance of a thousand suns were to burst at once into the sky, that would be like the splendor of the mighty one ...[236][237] Years later he would explain that another verse had also entered his head at that time: We knew the world would not be the same. A few people laughed, a few people cried. Most people were silent. I remembered the line from the Hindu scripture, the Bhagavad Gita; Vishnu is trying to persuade the Prince that he should do his duty and, to impress him, takes on his multi-armed form and says, 'Now I am become Death, the destroyer of worlds.' I suppose we all thought that, one way or another.[238][note 6] Personnel At its peak in June 1944, the Manhattan Project employed about 129,000 workers, of whom 84,500 were construction workers, 40,500 were plant operators and 1,800 were military personnel. As construction activity fell off, the workforce declined to 100,000 a year later, but the number of military personnel increased to 5,600. Procuring the required numbers of workers, especially highly skilled workers, in competition with other vital wartime programs proved very difficult.[242] Due to high turnover, over 500,000 people worked on the project.[243] In 1943, Groves obtained a special temporary priority for labor from the War Manpower Commission. In March 1944, both the War Production Board and the War Manpower Commission gave the project their highest priority.[244] The Kansas commission director stated that from April to July 1944 every qualified applicant in the state who visited a United States Employment Service office was urged to work at the Hanford Site. No other job was offered until the applicant definitively rejected the offer.[245] A large crowd of men and women in uniform listens to a fat man in uniform speaking at a microphone. They are wearing the Army Service Forces sleeve patch. The women are at the front and the men at the back. Beside him is the flag of the Army Corps of Engineers. Behind them are wooden two-storey buildings. Major General Leslie R. Groves, Jr., speaks to service personnel Oak Ridge Tennessee in August 1945. Tolman and Conant, in their role as the project's scientific advisers, drew up a list of candidate scientists and had them rated by scientists already working on the project. Groves then sent a personal letter to the head of their university or company asking for them to be released for essential war work.[246] At the University of Wisconsin–Madison, Stanislaw Ulam gave one of his students, Joan Hinton, an exam early, so she could leave to do war work. A few weeks later, Ulam received a letter from Hans Bethe, inviting him to join the project.[247] Conant personally persuaded Kistiakowsky to join the project.[248] One source of skilled personnel was the Army itself, particularly the Army Specialized Training Program. In 1943, the MED created the Special Engineer Detachment (SED), with an authorized strength of 675. Technicians and skilled workers drafted into the Army were assigned to the SED. Another source was the Women's Army Corps (WAC). Initially intended for clerical tasks handling classified material, the WACs were soon tapped for technical and scientific tasks as well.[249] On 1 February 1945, all military personnel assigned to the MED, including all SED detachments, were assigned to the 9812th Technical Service Unit, except at Los Alamos, where military personnel other than SED, including the WACs and Military Police, were assigned to the 4817th Service Command Unit.[250] An Associate Professor of Radiology at the University of Rochester School of Medicine, Stafford L. Warren, was commissioned as a colonel in the United States Army Medical Corps, and appointed as chief of the MED's Medical Section and Groves' medical advisor. Warren's initial task was to staff hospitals at Oak Ridge, Richland and Los Alamos.[251] The Medical Section was responsible for medical research, but also for the MED's health and safety programs. This presented an enormous challenge, because workers were handling a variety of toxic chemicals, using hazardous liquids and gases under high pressures, working with high voltages, and performing experiments involving explosives, not to mention the largely unknown dangers presented by radioactivity and handling fissile materials.[252] Yet in December 1945, the National Safety Council presented the Manhattan Project with the Award of Honor for Distinguished Service to Safety in recognition of its safety record. Between January 1943 and June 1945, there were 62 fatalities and 3,879 disabling injuries, which was about 62 percent below the rate of private industry.[253] Secrecy Uncle Sam has removed his hat and is rolling up his sleeves. On the wall in front of him are three monkeys and the slogan: What you see here/ What you do here/ What you hear here/ When you leave here/ Let it stay here. A billboard encouraging secrecy among Oak Ridge workers Byron Price, head of the government's Office of Censorship, called the Manhattan Project the best-kept secret of the war.[254] A 1945 Life article estimated that before the Hiroshima and Nagasaki bombings "probably no more than a few dozen men in the entire country knew the full meaning of the Manhattan Project, and perhaps only a thousand others even were aware that work on atoms was involved." The magazine wrote that the more than 100,000 others employed with the project "worked like moles in the dark". Warned that disclosing the project's secrets was punishable by 10 years in prison or a fine of US$10,000 (equivalent to $163,000 in 2022), they saw enormous quantities of raw materials enter factories with nothing coming out and monitored "dials and switches while behind thick concrete walls mysterious reactions took place" without knowing the purpose of their jobs.[255][256][257][258][259] In December 1945 the United States Army published a secret report analysing and assessing the security apparatus surrounding the Manhattan Project. The report states that the Manhattan Project was "more drastically guarded than any other highly secret war development." The security infrastructure surrounding the Manhattan Project was so vast and thorough that in the early days of the project in 1943, security investigators vetted 400,000 potential employees and 600 companies that would be involved in all aspects of the project for potential security risks.[260] Although at times the most important employer in the nation for government bureaucrats assigning manpower, they only knew of the "Pasco secret project"; one said that until Hiroshima "we had no idea what was being made".[245] Oak Ridge security personnel considered any private party with more than seven people as suspicious, and residents—who believed that US government agents were secretly among them—avoided repeatedly inviting the same guests. Although original residents of the area could be buried in existing cemeteries, every coffin was reportedly opened for inspection.[259] Everyone, including top military officials, and their automobiles were searched when entering and exiting project facilities. One Oak Ridge worker stated that "if you got inquisitive, you were called on the carpet within two hours by government secret agents. Usually those summoned to explain were then escorted bag and baggage to the gate and ordered to keep going".[261] Despite being told that their work would help end the war and perhaps all future wars,[261] not seeing or understanding the results of their often tedious duties—or even typical side effects of factory work such as smoke from smokestacks—and the war in Europe ending without the use of their work, caused serious morale problems among workers and caused many rumors to spread. One manager stated after the war: Well it wasn't that the job was tough ... it was confusing. You see, no one knew what was being made in Oak Ridge, not even me, and a lot of the people thought they were wasting their time here. It was up to me to explain to the dissatisfied workers that they were doing a very important job. When they asked me what, I'd have to tell them it was a secret. But I almost went crazy myself trying to figure out what was going on.[258] Another worker told of how, working in a laundry, she every day held "a special instrument" to uniforms and listened for "a clicking noise". She learned only after the war that she had been performing the important task of checking for radiation with a geiger counter. To improve morale among such workers Oak Ridge created an extensive system of intramural sports leagues, including 10 baseball teams, 81 softball teams, and 26 football teams.[258] Censorship Security poster, warning office workers to close drawers and put documents in safes when not being used Voluntary censorship of atomic information began before the Manhattan Project. After the start of the European war in 1939 American scientists began avoiding publishing military-related research, and in 1940 scientific journals began asking the National Academy of Sciences to clear articles. William L. Laurence of The New York Times, who wrote an article on atomic fission in The Saturday Evening Post of 7 September 1940, later learned that government officials asked librarians nationwide in 1943 to withdraw the issue.[262] The Soviets noticed the silence, however. In April 1942 nuclear physicist Georgy Flyorov wrote to Josef Stalin on the absence of articles on nuclear fission in American journals; this resulted in the Soviet Union establishing its own atomic bomb project.[263] The Manhattan Project operated under tight security lest its discovery induce Axis powers, especially Germany, to accelerate their own nuclear projects or undertake covert operations against the project.[264] The Office of Censorship, by contrast, relied on the press to comply with a voluntary code of conduct it published, and the project at first avoided notifying the office. By early 1943 newspapers began publishing reports of large construction in Tennessee and Washington based on public records, and the office began discussing with the project how to maintain secrecy. In June the Office of Censorship asked newspapers and broadcasters to avoid discussing "atom smashing, atomic energy, atomic fission, atomic splitting, or any of their equivalents. The use for military purposes of radium or radioactive materials, heavy water, high voltage discharge equipment, cyclotrons." The office also asked to avoid discussion of "polonium, uranium, ytterbium, hafnium, protactinium, radium, rhenium, thorium, deuterium"; only uranium was sensitive, but was listed with other elements to hide its importance.[265][254] Soviet spies Main article: Atomic spies The prospect of sabotage was always present, and sometimes suspected when there were equipment failures. While there were some problems believed to be the result of careless or disgruntled employees, there were no confirmed instances of Axis-instigated sabotage.[266] However, on 10 March 1945, a Japanese fire balloon struck a power line, and the resulting power surge caused the three reactors at Hanford to be temporarily shut down.[267] With so many people involved, security was a difficult task. A special Counter Intelligence Corps detachment was formed to handle the project's security issues.[268] By 1943, it was clear that the Soviet Union was attempting to penetrate the project. Lieutenant Colonel Boris T. Pash, the head of the Counter Intelligence Branch of the Defense Command, investigated suspected Soviet espionage at the Radiation Laboratory in Berkeley. Oppenheimer informed Pash that he had been approached by a fellow professor at Berkeley, Haakon Chevalier, about passing information to the Soviet Union.[269] The most successful Soviet spy was Klaus Fuchs, a member of the British Mission who played an important part at Los Alamos.[270] The 1950 revelation of his espionage activities damaged the United States' nuclear cooperation with Britain and Canada.[271] Subsequently, other instances of espionage were uncovered, leading to the arrest of Harry Gold, David Greenglass, and Julius and Ethel Rosenberg.[272] Other spies like George Koval and Theodore Hall remained unknown for decades.[273] The value of the espionage is difficult to quantify, as the principal constraint on the Soviet atomic bomb project was a shortage of uranium ore. The consensus is that espionage saved the Soviets one or two years of effort.[274] Foreign intelligence Main articles: Alsos Mission and Operation Epsilon Soldiers and workmen, some wearing steel helmet, clamber over what looks like a giant manhole. Allied soldiers dismantle the German experimental nuclear reactor at Haigerloch. In addition to developing the atomic bomb, the Manhattan Project was charged with gathering intelligence on the German nuclear energy project. It was believed that the Japanese nuclear weapons program was not far advanced because Japan had little access to uranium ore, but it was initially feared that Germany was very close to developing its own weapons. At the instigation of the Manhattan Project, a bombing and sabotage campaign was carried out against heavy water plants in German-occupied Norway.[275] A small mission was created, jointly staffed by the Office of Naval Intelligence, OSRD, the Manhattan Project, and Army Intelligence (G-2), to investigate enemy scientific developments. It was not restricted to those involving nuclear weapons.[276] The Chief of Army Intelligence, Major General George V. Strong, appointed Boris Pash to command the unit,[277] which was codenamed "Alsos", a Greek word meaning "grove".[278] The Alsos Mission to Italy questioned staff of the physics laboratory at the University of Rome following the capture of the city in June 1944.[279] Meanwhile, Pash formed a combined British and American Alsos mission in London under the command of Captain Horace K. Calvert to participate in Operation Overlord.[280] Groves considered the risk that the Germans might attempt to disrupt the Normandy landings with radioactive poisons was sufficient to warn General Dwight D. Eisenhower and send an officer to brief his chief of staff, Lieutenant General Walter Bedell Smith.[281] Under the codename Operation Peppermint, special equipment was prepared and Chemical Warfare Service teams were trained in its use.[282] Following in the wake of the advancing Allied armies, Pash and Calvert interviewed Frédéric Joliot-Curie about the activities of German scientists. They spoke to officials at Union Minière du Haut Katanga about uranium shipments to Germany. They tracked down 68 tons of ore in Belgium and 30 tons in France. The interrogation of German prisoners indicated that uranium and thorium were being processed in Oranienburg, 20 miles north of Berlin, so Groves arranged for it to be bombed on 15 March 1945.[283] An Alsos team went to Stassfurt in the Soviet Occupation Zone and retrieved 11 tons of ore from WIFO.[284] In April 1945, Pash, in command of a composite force known as T-Force, conducted Operation Harborage, a sweep behind enemy lines of the cities of Hechingen, Bisingen, and Haigerloch that were the heart of the German nuclear effort. T-Force captured the nuclear laboratories, documents, equipment and supplies, including heavy water and 1.5 tons of metallic uranium.[285][286] Alsos teams rounded up German scientists including Kurt Diebner, Otto Hahn, Walther Gerlach, Werner Heisenberg, and Carl Friedrich von Weizsäcker, who were taken to England where they were interned at Farm Hall, a bugged house in Godmanchester. After the bombs were detonated in Japan, the Germans were forced to confront the fact that the Allies had done what they could not.[287] Atomic bombings of Hiroshima and Nagasaki Main article: Atomic bombings of Hiroshima and Nagasaki Preparations A shiny metal four-engined aircraft stands on a runway. The crew pose in front of it. Silverplate B-29 Straight Flush. The tail code of the 444th Bombardment Group is painted on for security reasons. The only Allied aircraft capable of carrying the 17-foot (5.2 m) long Thin Man or the 59-inch (150 cm) wide Fat Man was the British Avro Lancaster, but using a British aircraft would have caused difficulties with maintenance. Groves hoped that the American Boeing B-29 Superfortress could be modified to carry Thin Man by joining its two bomb bays together.[288] This became unnecessary after Thin man was abandoned, as a Little Boy was short enough to fit into a B-29 bomb bay,[225] but modifications were still required. The Chief of United States Army Air Forces (USAAF), General Henry H. Arnold assured Groves that no effort would be spared to modify B-29s to do the job, and he designated Major General Oliver P. Echols as the USAAF liaison to the Manhattan Project. In turn, Echols named Colonel Roscoe C. Wilson as his alternate, and Wilson became Manhattan Project's main USAAF contact.[289] Commencing in November 1943, the Army Air Forces Materiel Command at Wright Field, Ohio, began Silverplate, the codename for the modification of the to carry atomic bombs. Test drops were carried out at Muroc Army Air Field and the Naval Ordnance Test Station in California with Thin Man and Fat Man pumpkin bombs to test their ballistic, fuzing and stability characteristics.[290] The 509th Composite Group was activated on 17 December 1944 at Wendover Army Air Field, Utah, under the command of Colonel Paul W. Tibbets. This base, close to the border with Nevada, was codenamed "Kingman" or "W-47". Training was conducted at Wendover and at Batista Army Airfield, Cuba, where the 393rd Bombardment Squadron practiced long-distance flights over water and dropped pumpkin bombs.[291] Roosevelt instructed Groves that if the atomic bombs were ready before the war with Germany ended, he should be ready to drop them on Germany, but Japan was regarded as the most likely target.[292] A special unit known as Project Alberta was formed at Los Alamos under Parsons's command to assist in preparing and delivering the bombs.[291] Commander Frederick L. Ashworth from Alberta met with Fleet Admiral Chester W. Nimitz on Guam in February 1945 to inform him of the Manhattan Project. While he was there, Ashworth selected North Field on Tinian as a base for the 509th Composite Group, and he reserved space for the group and its buildings. The group deployed there in July 1945.[293] Farrell arrived at Tinian on 30 July as the Manhattan Project representative.[294] Purnell went to Tinian as the representative of the Military Policy Committee.[294] Most of the components for Little Boy left San Francisco on the cruiser USS Indianapolis on 16 July and arrived on Tinian on 26 July. Four days later the ship was sunk by a Japanese submarine. The remaining components, which included six highly enriched uranium rings, were delivered by three Douglas C-54 Skymasters of the 509th Group's 320th Troop Carrier Squadron.[295] Two Fat Man assemblies travelled to Tinian in specially modified 509th Composite Group B-29s. The first plutonium core went in a special C-54.[296] In late April, a joint targeting committee of the Manhattan District and USAAF was established to determine which cities in Japan should be targets, and recommended Kokura, Hiroshima, Niigata, and Kyoto. At this point, Secretary of War Henry L. Stimson intervened, announcing that he would be making the targeting decision, and that he would not authorize the bombing of Kyoto on the grounds of its historical and religious significance. Groves therefore asked Arnold to remove Kyoto not just from the list of nuclear targets, but from targets for conventional bombing as well.[297] Nagasaki was substituted.[298] Bombings In May 1945, the Interim Committee was created to advise on wartime and postwar use of nuclear energy. The committee was chaired by Stimson, with James F. Byrnes, a former US Senator soon to be Secretary of State, as President Harry S. Truman's personal representative; Ralph A. Bard, the Under Secretary of the Navy; William L. Clayton, the Assistant Secretary of State; Vannevar Bush; Karl T. Compton; James B. Conant; and George L. Harrison, an assistant to Stimson and president of New York Life Insurance Company. The Interim Committee in turn established a scientific panel consisting of Arthur Compton, Fermi, Lawrence and Oppenheimer to advise it on scientific issues. In its presentation to the Interim Committee, the scientific panel offered its opinion not just on the likely physical effects of an atomic bomb, but on its probable military and political impact.[299] At the Potsdam Conference in Germany, Truman was informed that the Trinity test had been successful. He told Stalin, the leader of the Soviet Union, that the US had a new superweapon, without giving any details. This was the first official communication to the Soviet Union about the bomb, but Stalin already knew about it from spies.[300] With the authorization to use the bomb against Japan already given, no alternatives were considered after the Japanese rejection of the Potsdam Declaration.[301] Two mushroom clouds rise vertically. Little Boy explodes over Hiroshima, Japan, 6 August 1945 (left); Fat Man explodes over Nagasaki, Japan, 9 August 1945 (right). On 6 August 1945, a Boeing B-29 Superfortress (Enola Gay) of the 393d Bombardment Squadron, piloted by Tibbets, lifted off from North Field with a Little Boy in its bomb bay. Hiroshima, the headquarters of the 2nd General Army and Fifth Division and a port of embarkation, was the primary target of the mission, with Kokura and Nagasaki as alternatives. With Farrell's permission, Parsons, the weaponeer in charge of the mission, completed the bomb assembly in the air to minimize the risks of a nuclear explosion in the event of a crash during takeoff.[302] The bomb detonated at an altitude of 1,750 feet (530 m) with a blast that was later estimated to be the equivalent of 13 kilotons of TNT.[303] An area of approximately 4.7 square miles (12 km2) was destroyed. Japanese officials determined that 69% of Hiroshima's buildings were destroyed and another 6–7% damaged. About 70,000 to 80,000 people, of whom 20,000 were Japanese combatants and 20,000 were Korean slave laborers, or some 30% of the population of Hiroshima, were killed immediately, and another 70,000 injured.[304][305][306] On the morning of 9 August 1945, a second B-29 (Bockscar), piloted by the 393d Bombardment Squadron's commander, Major Charles W. Sweeney, lifted off with a Fat Man on board. This time, Ashworth served as weaponeer and Kokura was the primary target. Sweeney took off with the weapon already armed but with the electrical safety plugs still engaged. When they reached Kokura, they found cloud cover had obscured the city, prohibiting the visual attack required by orders. After three runs over the city, and with fuel running low, they headed for the secondary target, Nagasaki. Ashworth decided that a radar approach would be used if the target was obscured, but a last-minute break in the clouds over Nagasaki allowed a visual approach as ordered. The Fat Man was dropped over the city's industrial valley midway between the Mitsubishi Steel and Arms Works in the south and the Mitsubishi-Urakami Ordnance Works in the north. The resulting explosion had a blast yield equivalent to 21 kilotons of TNT, roughly the same as the Trinity blast, but was confined to the Urakami Valley, and a major portion of the city was protected by the intervening hills, resulting in the destruction of about 44% of the city. The bombing also crippled the city's industrial production extensively and killed 23,200–28,200 Japanese industrial workers and 150 Japanese soldiers.[307] Overall, an estimated 35,000–40,000 people were killed and 60,000 injured.[308][309] Groves expected to have another atomic bomb ready for use on 19 August, with three more in September and a further three in October.[310] Two more Fat Man assemblies were readied, and scheduled to leave Kirtland Field for Tinian on 11 and 14 August.[309] At Los Alamos, technicians worked 24 hours straight to cast another plutonium core.[311] Although cast, it still needed to be pressed and coated, which would take until 16 August.[312] It could therefore have been ready for use on 19 August. On 10 August, Truman secretly requested that additional atomic bombs not be dropped on Japan without his express authority.[313] Groves suspended the third core's shipment on his own authority on 13 August.[313] On 11 August, Groves phoned Warren with orders to organize a survey team to report on the damage and radioactivity at Hiroshima and Nagasaki. A party equipped with portable Geiger counters arrived in Hiroshima on 8 September headed by Farrell and Warren, with Japanese Rear Admiral Masao Tsuzuki, who acted as a translator. They remained in Hiroshima until 14 September and then surveyed Nagasaki from 19 September to 8 October.[314] This and other scientific missions to Japan provided valuable scientific and historical data.[315] The necessity of the bombings of Hiroshima and Nagasaki became a subject of controversy among historians. Some questioned whether an "atomic diplomacy" would not have attained the same goals and disputed whether the bombings or the Soviet declaration of war on Japan was decisive.[310] The Franck Report was the most notable effort pushing for a demonstration but was turned down by the Interim Committee's scientific panel.[316] The Szilárd petition, drafted in July 1945 and signed by dozens of scientists working on the Manhattan Project, was a late attempt at warning President Harry S. Truman about his responsibility in using such weapons.[317][318] After the war Men in suits and uniforms stand on a dais decorated with bunting and salute. Presentation of the Army–Navy "E" Award at Los Alamos on 16 October 1945. Standing, left to right: J. Robert Oppenheimer, unidentified, unidentified, Kenneth Nichols, Leslie Groves, Robert Gordon Sproul, William Sterling Parsons. Seeing the work they had not understood produce the Hiroshima and Nagasaki bombs amazed the workers of the Manhattan Project as much as the rest of the world; newspapers in Oak Ridge announcing the Hiroshima bomb sold for $1 ($12 today).[256][254] Although the bombs' existence was public, secrecy continued, and many workers remained ignorant of their jobs; one stated in 1946, "I don't know what the hell I'm doing besides looking into a ——— and turning a ——— alongside a ———. I don't know anything about it, and there's nothing to say". Many residents continued to avoid discussion of "the stuff" in ordinary conversation despite it being the reason for their town's existence.[259] In anticipation of the bombings, Groves had Henry DeWolf Smyth prepare a history for public consumption. Atomic Energy for Military Purposes, better known as the "Smyth Report", was released to the public on 12 August 1945.[319] Groves and Nichols presented Army–Navy "E" Awards to key contractors, whose involvement had hitherto been secret. Over 20 awards of the Presidential Medal for Merit were made to key contractors and scientists, including Bush and Oppenheimer. Military personnel received the Legion of Merit, including the commander of the Women's Army Corps detachment, Captain Arlene G. Scheidenhelm.[320] At Hanford, plutonium production fell off as Reactors B, D and F wore out, poisoned by fission products and swelling of the graphite moderator known as the Wigner effect. The swelling damaged the charging tubes where the uranium was irradiated to produce plutonium, rendering them unusable. In order to maintain the supply of polonium for the urchin initiators, production was curtailed and the oldest unit, B pile, was closed down so at least one reactor would be available in the future. Research continued, with DuPont and the Metallurgical Laboratory developing a redox solvent extraction process as an alternative plutonium extraction technique to the bismuth phosphate process, which left unspent uranium in a state from which it could not easily be recovered.[321] Bomb engineering was carried out by the Z Division, named for its director, Dr. Jerrold R. Zacharias from Los Alamos.[322] Z Division was initially located at Wendover Field but moved to Oxnard Field, New Mexico, in September 1945 to be closer to Los Alamos. This marked the beginning of Sandia Base. Nearby Kirtland Field was used as a B-29 base for aircraft compatibility and drop tests.[323] By October, all the staff and facilities at Wendover had been transferred to Sandia.[324] As reservist officers were demobilized, they were replaced by about fifty hand-picked regular officers.[325] Nichols recommended that S-50 and the Alpha tracks at Y-12 be closed down. This was done in September.[326] Although performing better than ever,[327] the Alpha tracks could not compete with K-25 and the new K-27, which had commenced operation in January 1946. In December, the Y-12 plant was closed, thereby cutting the Tennessee Eastman payroll from 8,600 to 1,500 and saving $2 million a month.[328] A man in a suit is seated at a desk, signing a document. Seven men in suits gather around him. President Harry S. Truman signs the Atomic Energy Act of 1946, establishing the United States Atomic Energy Commission. Nowhere was demobilization more of a problem than at Los Alamos, where there was an exodus of talent. Much remained to be done. The bombs used on Hiroshima and Nagasaki were like laboratory pieces; work would be required to make them simpler, safer and more reliable. Implosion methods needed to be developed for uranium in place of the wasteful gun method, and composite uranium-plutonium cores were needed now that plutonium was in short supply because of the problems with the reactors. However, uncertainty about the future of the laboratory made it hard to induce people to stay. Oppenheimer returned to his job at the University of California and Groves appointed Norris Bradbury as an interim replacement; Bradbury remained in the post for the next 25 years.[324] Groves attempted to combat the dissatisfaction caused by the lack of amenities with a construction program that included an improved water supply, three hundred houses, and recreation facilities.[321] Two Fat Man-type detonations were conducted at Bikini Atoll in July 1946 as part of Operation Crossroads to investigate the effect of nuclear weapons on warships.[329] Able was detonated on 1 July 1946. The more spectacular Baker was detonated underwater on 25 July 1946.[330] After the bombings at Hiroshima and Nagasaki, a number of Manhattan Project physicists founded the Bulletin of the Atomic Scientists, which began as an emergency action undertaken by scientists who saw urgent need for an immediate educational program about atomic weapons.[331] In the face of the destructiveness of the new weapons and in anticipation of the nuclear arms race several project members including Bohr, Bush and Conant expressed the view that it was necessary to reach agreement on international control of nuclear research and atomic weapons. The Baruch Plan, unveiled in a speech to the newly formed United Nations Atomic Energy Commission (UNAEC) in June 1946, proposed the establishment of an international atomic development authority, but was not adopted.[332] Following a domestic debate over the permanent management of the nuclear program, the United States Atomic Energy Commission (AEC) was created by the Atomic Energy Act of 1946 to take over the functions and assets of the Manhattan Project. It established civilian control over atomic development, and separated the development, production and control of atomic weapons from the military. Military aspects were taken over by the Armed Forces Special Weapons Project (AFSWP).[333] Although the Manhattan Project ceased to exist on 31 December 1946, the Manhattan District was not abolished until 15 August 1947.[334] Cost Manhattan Project costs through 31 December 1945[335] Site Cost (1945 USD) Cost (2021 USD) % of total Oak Ridge $1.19 billion $14.4 billion 62.9% Hanford $390 million $4.72 billion 20.6% Special operating materials $103 million $1.25 billion 5.5% Los Alamos $74.1 million $895 million 3.9% Research and development $69.7 million $843 million 3.7% Government overhead $37.3 million $450 million 2.0% Heavy water plants $26.8 million $324 million 1.4% Total $1.89 billion $22.8 billion The project expenditure through 1 October 1945 was $1.845 billion, equivalent to less than nine days of wartime spending, and was $2.191 billion when the AEC assumed control on 1 January 1947. Total allocation was $2.4 billion. Over 90% of the cost was for building plants and producing the fissionable materials, and less than 10% for development and production of the weapons.[336][337] A total of four weapons (the Trinity gadget, Little Boy, Fat Man, and an unused Fat Man bomb) were produced by the end of 1945, making the average cost per bomb around $500 million in 1945 dollars. By comparison, the project's total cost by the end of 1945 was about 90% of the total spent on the production of US small arms (not including ammunition) and 34% of the total spent on US tanks during the same period.[335] Overall, it was the second most expensive weapons project undertaken by the United States in World War II, behind only the design and production of the Boeing B-29 Superfortress.[338] Legacy See also: Nuclear weapons in popular culture The Lake Ontario Ordnance Works (LOOW) near Niagara Falls became a principal repository for Manhattan Project waste for the Eastern United States.[339] All of the radioactive materials stored at the LOOW site—including thorium, uranium, and the world's largest concentration of radium-226—were buried in an "Interim Waste Containment Structure" (in the foreground) in 1991.[340][341][342] The political and cultural impacts of the development of nuclear weapons were profound and far-reaching. William Laurence of The New York Times, the first to use the phrase "Atomic Age",[343] became the official correspondent for the Manhattan Project in spring 1945. In 1943 and 1944 he unsuccessfully attempted to persuade the Office of Censorship to permit writing about the explosive potential of uranium, and government officials felt that he had earned the right to report on the biggest secret of the war. Laurence witnessed both the Trinity test[344] and the bombing of Nagasaki and wrote the official press releases prepared for them. He went on to write a series of articles extolling the virtues of the new weapon. His reporting before and after the bombings helped to spur public awareness of the potential of nuclear technology and motivated its development in the United States and the Soviet Union.[345] The wartime Manhattan Project left a legacy in the form of the network of national laboratories: the Lawrence Berkeley National Laboratory, Los Alamos National Laboratory, Oak Ridge National Laboratory, Argonne National Laboratory, and Ames Laboratory. Two more were established by Groves soon after the war, the Brookhaven National Laboratory at Upton, New York, and the Sandia National Laboratories at Albuquerque, New Mexico. Groves allocated $72 million to them for research activities in fiscal year 1946–1947.[346] They would be in the vanguard of the kind of large-scale research that Alvin Weinberg, the director of the Oak Ridge National Laboratory, would call Big Science.[347] The Naval Research Laboratory had long been interested in the prospect of using nuclear power for warship propulsion, and sought to create its own nuclear project. In May 1946, Nimitz, now Chief of Naval Operations, decided that the Navy should instead work with the Manhattan Project. A group of naval officers were assigned to Oak Ridge, the most senior of whom was Captain Hyman G. Rickover, who became assistant director there. They immersed themselves in the study of nuclear energy, laying the foundations for a nuclear-powered navy.[348] A similar group of Air Force personnel arrived at Oak Ridge in September 1946 with the aim of developing nuclear aircraft.[349] Their Nuclear Energy for the Propulsion of Aircraft (NEPA) project ran into formidable technical difficulties, and was ultimately cancelled.[350] The ability of the new reactors to create radioactive isotopes in previously unheard-of quantities sparked a revolution in nuclear medicine in the immediate postwar years. Starting in mid-1946, Oak Ridge began distributing radioisotopes to hospitals and universities. Most of the orders were for iodine-131 and phosphorus-32, which were used in the diagnosis and treatment of cancer. In addition to medicine, isotopes were also used in biological, industrial and agricultural research.[351] On handing over control to the Atomic Energy Commission, Groves bid farewell to the people who had worked on the Manhattan Project: Five years ago, the idea of Atomic Power was only a dream. You have made that dream a reality. You have seized upon the most nebulous of ideas and translated them into actualities. You have built cities where none were known before. You have constructed industrial plants of a magnitude and to a precision heretofore deemed impossible. You built the weapon which ended the War and thereby saved countless American lives. With regard to peacetime applications, you have raised the curtain on vistas of a new world.[352] In 2014, the United States Congress passed a law providing for a national park dedicated to the history of the Manhattan Project.[353] The Manhattan Project National Historical Park was established on 10 November 2015.[354] Notes A nuclear weapon[a] is an explosive device that derives its destructive force from nuclear reactions, either fission (fission bomb) or a combination of fission and fusion reactions (thermonuclear bomb), producing a nuclear explosion. Both bomb types release large quantities of energy from relatively small amounts of matter. The first test of a fission ("atomic") bomb released an amount of energy approximately equal to 20,000 tons of TNT (84 TJ).[1] The first thermonuclear ("hydrogen") bomb test released energy approximately equal to 10 million tons of TNT (42 PJ). Nuclear bombs have had yields between 10 tons TNT (the W54) and 50 megatons for the Tsar Bomba (see TNT equivalent). A thermonuclear weapon weighing as little as 600 pounds (270 kg) can release energy equal to more than 1.2 megatonnes of TNT (5.0 PJ).[2] A nuclear device no larger than a conventional bomb can devastate an entire city by blast, fire, and radiation. Since they are weapons of mass destruction, the proliferation of nuclear weapons is a focus of international relations policy. Nuclear weapons have been deployed twice in war, by the United States against the Japanese cities of Hiroshima and Nagasaki in 1945 during World War II. Testing and deployment Nuclear weapons have only twice been used in war, both times by the United States against Japan near the end of World War II. On August 6, 1945, the U.S. Army Air Forces detonated a uranium gun-type fission bomb nicknamed "Little Boy" over the Japanese city of Hiroshima; three days later, on August 9, the U.S. Army Air Forces detonated a plutonium implosion-type fission bomb nicknamed "Fat Man" over the Japanese city of Nagasaki. These bombings caused injuries that resulted in the deaths of approximately 200,000 civilians and military personnel.[3] The ethics of these bombings and their role in Japan's surrender are subjects of debate. Since the atomic bombings of Hiroshima and Nagasaki, nuclear weapons have been detonated over 2,000 times for testing and demonstration. Only a few nations possess such weapons or are suspected of seeking them. The only countries known to have detonated nuclear weapons—and acknowledge possessing them—are (chronologically by date of first test) the United States, the Soviet Union (succeeded as a nuclear power by Russia), the United Kingdom, France, China, India, Pakistan, and North Korea. Israel is believed to possess nuclear weapons, though, in a policy of deliberate ambiguity, it does not acknowledge having them. Germany, Italy, Turkey, Belgium and the Netherlands are nuclear weapons sharing states.[4][5][b] South Africa is the only country to have independently developed and then renounced and dismantled its nuclear weapons.[6] The Treaty on the Non-Proliferation of Nuclear Weapons aims to reduce the spread of nuclear weapons, but its effectiveness has been questioned. Modernisation of weapons continues to this day.[7] Types Main article: Nuclear weapon design The Trinity test of the Manhattan Project was the first detonation of a nuclear weapon, which led J. Robert Oppenheimer to recall verses from the Hindu scripture Bhagavad Gita: "If the radiance of a thousand suns were to burst at once into the sky, that would be like the splendor of the mighty one "... "I am become Death, the destroyer of worlds".[8] Robert Oppenheimer, principal leader of the Manhattan Project, often referred to as the "father of the atomic bomb". There are two basic types of nuclear weapons: those that derive the majority of their energy from nuclear fission reactions alone, and those that use fission reactions to begin nuclear fusion reactions that produce a large amount of the total energy output.[9] Fission weapons The two basic fission weapon designs All existing nuclear weapons derive some of their explosive energy from nuclear fission reactions. Weapons whose explosive output is exclusively from fission reactions are commonly referred to as atomic bombs or atom bombs (abbreviated as A-bombs). This has long been noted as something of a misnomer, as their energy comes from the nucleus of the atom, just as it does with fusion weapons. In fission weapons, a mass of fissile material (enriched uranium or plutonium) is forced into supercriticality—allowing an exponential growth of nuclear chain reactions—either by shooting one piece of sub-critical material into another (the "gun" method) or by compression of a sub-critical sphere or cylinder of fissile material using chemically fueled explosive lenses. The latter approach, the "implosion" method, is more sophisticated and more efficient (smaller, less massive, and requiring less of the expensive fissile fuel) than the former. A major challenge in all nuclear weapon designs is to ensure that a significant fraction of the fuel is consumed before the weapon destroys itself. The amount of energy released by fission bombs can range from the equivalent of just under a ton to upwards of 500,000 tons (500 kilotons) of TNT (4.2 to 2.1×106 GJ).[10] All fission reactions generate fission products, the remains of the split atomic nuclei. Many fission products are either highly radioactive (but short-lived) or moderately radioactive (but long-lived), and as such, they are a serious form of radioactive contamination. Fission products are the principal radioactive component of nuclear fallout. Another source of radioactivity is the burst of free neutrons produced by the weapon. When they collide with other nuclei in the surrounding material, the neutrons transmute those nuclei into other isotopes, altering their stability and making them radioactive. The most commonly used fissile materials for nuclear weapons applications have been uranium-235 and plutonium-239. Less commonly used has been uranium-233. Neptunium-237 and some isotopes of americium may be usable for nuclear explosives as well, but it is not clear that this has ever been implemented, and their plausible use in nuclear weapons is a matter of dispute.[11] Fusion weapons Main article: Thermonuclear weapon The basics of the Teller–Ulam design for a hydrogen bomb: a fission bomb uses radiation to compress and heat a separate section of fusion fuel. The other basic type of nuclear weapon produces a large proportion of its energy in nuclear fusion reactions. Such fusion weapons are generally referred to as thermonuclear weapons or more colloquially as hydrogen bombs (abbreviated as H-bombs), as they rely on fusion reactions between isotopes of hydrogen (deuterium and tritium). All such weapons derive a significant portion of their energy from fission reactions used to "trigger" fusion reactions, and fusion reactions can themselves trigger additional fission reactions.[12] Only six countries—United States, Russia, United Kingdom, China, France, and India—have conducted thermonuclear weapon tests. Whether India has detonated a "true" multi-staged thermonuclear weapon is controversial.[13] North Korea claims to have tested a fusion weapon as of January 2016, though this claim is disputed.[14] Thermonuclear weapons are considered much more difficult to successfully design and execute than primitive fission weapons. Almost all of the nuclear weapons deployed today use the thermonuclear design because it is more efficient.[15] Thermonuclear bombs work by using the energy of a fission bomb to compress and heat fusion fuel. In the Teller-Ulam design, which accounts for all multi-megaton yield hydrogen bombs, this is accomplished by placing a fission bomb and fusion fuel (tritium, deuterium, or lithium deuteride) in proximity within a special, radiation-reflecting container. When the fission bomb is detonated, gamma rays and X-rays emitted first compress the fusion fuel, then heat it to thermonuclear temperatures. The ensuing fusion reaction creates enormous numbers of high-speed neutrons, which can then induce fission in materials not normally prone to it, such as depleted uranium. Each of these components is known as a "stage", with the fission bomb as the "primary" and the fusion capsule as the "secondary". In large, megaton-range hydrogen bombs, about half of the yield comes from the final fissioning of depleted uranium.[10] Virtually all thermonuclear weapons deployed today use the "two-stage" design described above, but it is possible to add additional fusion stages—each stage igniting a larger amount of fusion fuel in the next stage. This technique can be used to construct thermonuclear weapons of arbitrarily large yield. This is in contrast to fission bombs, which are limited in their explosive power due to criticality danger (premature nuclear chain reaction caused by too-large amounts of pre-assembled fissile fuel). The largest nuclear weapon ever detonated, the Tsar Bomba of the USSR, which released an energy equivalent of over 50 megatons of TNT (210 PJ), was a three-stage weapon. Most thermonuclear weapons are considerably smaller than this, due to practical constraints from missile warhead space and weight requirements.[16] Edward Teller, often referred to as the "father of the hydrogen bomb" Fusion reactions do not create fission products, and thus contribute far less to the creation of nuclear fallout than fission reactions, but because all thermonuclear weapons contain at least one fission stage, and many high-yield thermonuclear devices have a final fission stage, thermonuclear weapons can generate at least as much nuclear fallout as fission-only weapons. Furthermore, high yield thermonuclear explosions (most dangerously ground bursts) have the force to lift radioactive debris upwards past the tropopause into the stratosphere, where the calm non-turbulent winds permit the debris to travel great distances from the burst, eventually settling and unpredictably contaminating areas far removed from the target of the explosion. Other types Main articles: Boosted fission weapon, Neutron bomb, Radiological warfare, Induced gamma emission, and Antimatter weapon There are other types of nuclear weapons as well. For example, a boosted fission weapon is a fission bomb that increases its explosive yield through a small number of fusion reactions, but it is not a fusion bomb. In the boosted bomb, the neutrons produced by the fusion reactions serve primarily to increase the efficiency of the fission bomb. There are two types of boosted fission bomb: internally boosted, in which a deuterium-tritium mixture is injected into the bomb core, and externally boosted, in which concentric shells of lithium-deuteride and depleted uranium are layered on the outside of the fission bomb core. The external method of boosting enabled the USSR to field the first partially-thermonuclear weapons, but it is now obsolete because it demands a spherical bomb geometry, which was adequate during the 1950s arms race when bomber aircraft were the only available delivery vehicles. The detonation of any nuclear weapon is accompanied by a blast of neutron radiation. Surrounding a nuclear weapon with suitable materials (such as cobalt or gold) creates a weapon known as a salted bomb. This device can produce exceptionally large quantities of long-lived radioactive contamination. It has been conjectured that such a device could serve as a "doomsday weapon" because such a large quantity of radioactivities with half-lives of decades, lifted into the stratosphere where winds would distribute it around the globe, would make all life on the planet extinct. In connection with the Strategic Defense Initiative, research into the nuclear pumped laser was conducted under the DOD program Project Excalibur but this did not result in a working weapon. The concept involves the tapping of the energy of an exploding nuclear bomb to power a single-shot laser that is directed at a distant target. During the Starfish Prime high-altitude nuclear test in 1962, an unexpected effect was produced which is called a nuclear electromagnetic pulse. This is an intense flash of electromagnetic energy produced by a rain of high-energy electrons which in turn are produced by a nuclear bomb's gamma rays. This flash of energy can permanently destroy or disrupt electronic equipment if insufficiently shielded. It has been proposed to use this effect to disable an enemy's military and civilian infrastructure as an adjunct to other nuclear or conventional military operations. By itself it could as well be useful to terrorists for crippling a nation's economic electronics-based infrastructure. Because the effect is most effectively produced by high altitude nuclear detonations (by military weapons delivered by air, though ground bursts also produce EMP effects over a localized area), it can produce damage to electronics over a wide, even continental, geographical area. Research has been done into the possibility of pure fusion bombs: nuclear weapons that consist of fusion reactions without requiring a fission bomb to initiate them. Such a device might provide a simpler path to thermonuclear weapons than one that required the development of fission weapons first, and pure fusion weapons would create significantly less nuclear fallout than other thermonuclear weapons because they would not disperse fission products. In 1998, the United States Department of Energy divulged that the United States had, "...made a substantial investment" in the past to develop pure fusion weapons, but that, "The U.S. does not have and is not developing a pure fusion weapon", and that, "No credible design for a pure fusion weapon resulted from the DOE investment".[17] Nuclear isomers provide a possible pathway to fissionless fusion bombs. These are naturally occurring isotopes (178m2Hf being a prominent example) which exist in an elevated energy state. Mechanisms to release this energy as bursts of gamma radiation (as in the hafnium controversy) have been proposed as possible triggers for conventional thermonuclear reactions. Antimatter, which consists of particles resembling ordinary matter particles in most of their properties but having opposite electric charge, has been considered as a trigger mechanism for nuclear weapons.[18][19][20] A major obstacle is the difficulty of producing antimatter in large enough quantities, and there is no evidence that it is feasible beyond the military domain.[21] However, the U.S. Air Force funded studies of the physics of antimatter in the Cold War, and began considering its possible use in weapons, not just as a trigger, but as the explosive itself.[22] A fourth generation nuclear weapon design[18] is related to, and relies upon, the same principle as antimatter-catalyzed nuclear pulse propulsion.[23] Most variation in nuclear weapon design is for the purpose of achieving different yields for different situations, and in manipulating design elements to attempt to minimize weapon size,[10] radiation hardness or requirements for special materials, especially fissile fuel or tritium. Tactical nuclear weapons Soviet OTR-21 Tochka missile. Capable of firing a 100 kiloton nuclear warhead a distance of 185 km Some nuclear weapons are designed for special purposes; most of these are for non-strategic (decisively war-winning) purposes and are referred to as tactical nuclear weapons. The neutron bomb purportedly conceived by Sam Cohen is a thermonuclear weapon that yields a relatively small explosion but a relatively large amount of neutron radiation. Such a weapon could, according to tacticians, be used to cause massive biological casualties while leaving inanimate infrastructure mostly intact and creating minimal fallout. Because high energy neutrons are capable of penetrating dense matter, such as tank armor, neutron warheads were procured in the 1980s (though not deployed in Europe, as intended, over the objections of NATO allies) for use as tactical payloads for US Army artillery shells (200 mm W79 and 155 mm W82) and short range missile forces. Soviet authorities announced similar intentions for neutron warhead deployment in Europe; indeed claimed to have originally invented the neutron bomb, but their deployment on USSR tactical nuclear forces is unverifiable.[citation needed] A type of nuclear explosive most suitable for use by ground special forces was the Special Atomic Demolition Munition, or SADM, sometimes popularly known as a suitcase nuke. This is a nuclear bomb that is man-portable, or at least truck-portable, and though of a relatively small yield (one or two kilotons) is sufficient to destroy important tactical targets such as bridges, dams, tunnels, important military or commercial installations, etc. either behind enemy lines or pre-emptively on friendly territory soon to be overtaken by invading enemy forces. These weapons require plutonium fuel and are particularly "dirty". They also demand especially stringent security precautions in their storage and deployment.[citation needed] Small "tactical" nuclear weapons were deployed for use as antiaircraft weapons. Examples include the USAF AIR-2 Genie, the AIM-26 Falcon and US Army Nike Hercules. Missile interceptors such as the Sprint and the Spartan also used small nuclear warheads (optimized to produce neutron or X-ray flux) but were for use against enemy strategic warheads.[citation needed] Other small, or tactical, nuclear weapons were deployed by naval forces for use primarily as antisubmarine weapons. These included nuclear depth bombs or nuclear armed torpedoes. Nuclear mines for use on land or at sea are also possibilities.[citation needed] Weapons delivery See also: Nuclear weapons delivery, Nuclear triad, Strategic bomber, Intercontinental ballistic missile, and Submarine-launched ballistic missile The first nuclear weapons were gravity bombs, such as this "Fat Man" weapon dropped on Nagasaki, Japan. They were large and could only be delivered by heavy bomber aircraft A demilitarized, commercial launch of the Russian Strategic Rocket Forces R-36 ICBM; also known by the NATO reporting name: SS-18 Satan. Upon its first fielding in the late 1960s, the SS-18 remains the single highest throw weight missile delivery system ever built. The system used to deliver a nuclear weapon to its target is an important factor affecting both nuclear weapon design and nuclear strategy. The design, development, and maintenance of delivery systems are among the most expensive parts of a nuclear weapons program; they account, for example, for 57% of the financial resources spent by the United States on nuclear weapons projects since 1940.[24] The simplest method for delivering a nuclear weapon is a gravity bomb dropped from aircraft; this was the method used by the United States against Japan. This method places few restrictions on the size of the weapon. It does, however, limit attack range, response time to an impending attack, and the number of weapons that a country can field at the same time. With miniaturization, nuclear bombs can be delivered by both strategic bombers and tactical fighter-bombers. This method is the primary means of nuclear weapons delivery; the majority of U.S. nuclear warheads, for example, are free-fall gravity bombs, namely the B61.[10][needs update] Montage of an inert test of a United States Trident SLBM (submarine launched ballistic missile), from submerged to the terminal, or re-entry phase, of the multiple independently targetable reentry vehicles Preferable from a strategic point of view is a nuclear weapon mounted on a missile, which can use a ballistic trajectory to deliver the warhead over the horizon. Although even short-range missiles allow for a faster and less vulnerable attack, the development of long-range intercontinental ballistic missiles (ICBMs) and submarine-launched ballistic missiles (SLBMs) has given some nations the ability to plausibly deliver missiles anywhere on the globe with a high likelihood of success. More advanced systems, such as multiple independently targetable reentry vehicles (MIRVs), can launch multiple warheads at different targets from one missile, reducing the chance of a successful missile defense. Today, missiles are most common among systems designed for delivery of nuclear weapons. Making a warhead small enough to fit onto a missile, though, can be difficult.[10] Tactical weapons have involved the most variety of delivery types, including not only gravity bombs and missiles but also artillery shells, land mines, and nuclear depth charges and torpedoes for anti-submarine warfare. An atomic mortar has been tested by the United States. Small, two-man portable tactical weapons (somewhat misleadingly referred to as suitcase bombs), such as the Special Atomic Demolition Munition, have been developed, although the difficulty of combining sufficient yield with portability limits their military utility.[10] Nuclear strategy Main articles: Nuclear strategy and Deterrence theory See also: Pre-emptive nuclear strike, Nuclear peace, Essentials of Post–Cold War Deterrence, Single Integrated Operational Plan, Nuclear warfare, and On Thermonuclear War Nuclear warfare strategy is a set of policies that deal with preventing or fighting a nuclear war. The policy of trying to prevent an attack by a nuclear weapon from another country by threatening nuclear retaliation is known as the strategy of nuclear deterrence. The goal in deterrence is to always maintain a second strike capability (the ability of a country to respond to a nuclear attack with one of its own) and potentially to strive for first strike status (the ability to destroy an enemy's nuclear forces before they could retaliate). During the Cold War, policy and military theorists considered the sorts of policies that might prevent a nuclear attack, and they developed game theory models that could lead to stable deterrence conditions.[25] The now decommissioned United States' Peacekeeper missile was an ICBM developed to replace the Minuteman missile in the late 1980s. Each missile, like the heavier lift Russian SS-18 Satan, could contain up to ten nuclear warheads (shown in red), each of which could be aimed at a different target. A factor in the development of MIRVs was to make complete missile defense difficult for an enemy country. Different forms of nuclear weapons delivery (see above) allow for different types of nuclear strategies. The goals of any strategy are generally to make it difficult for an enemy to launch a pre-emptive strike against the weapon system and difficult to defend against the delivery of the weapon during a potential conflict. This can mean keeping weapon locations hidden, such as deploying them on submarines or land mobile transporter erector launchers whose locations are difficult to track, or it can mean protecting weapons by burying them in hardened missile silo bunkers. Other components of nuclear strategies included using missile defenses to destroy the missiles before they land, or implementing civil defense measures using early-warning systems to evacuate citizens to safe areas before an attack. Weapons designed to threaten large populations or to deter attacks are known as strategic weapons. Nuclear weapons for use on a battlefield in military situations are called tactical weapons. Critics of nuclear war strategy often suggest that a nuclear war between two nations would result in mutual annihilation. From this point of view, the significance of nuclear weapons is to deter war because any nuclear war would escalate out of mutual distrust and fear, resulting in mutually assured destruction. This threat of national, if not global, destruction has been a strong motivation for anti-nuclear weapons activism. Critics from the peace movement and within the military establishment[citation needed] have questioned the usefulness of such weapons in the current military climate. According to an advisory opinion issued by the International Court of Justice in 1996, the use of (or threat of use of) such weapons would generally be contrary to the rules of international law applicable in armed conflict, but the court did not reach an opinion as to whether or not the threat or use would be lawful in specific extreme circumstances such as if the survival of the state were at stake. Ballistic missile submarines have been of great strategic importance for the United States, Russia, and other nuclear powers since they entered service in the Cold War, as they can hide from reconnaissance satellites and fire their nuclear weapons with virtual impunity. Another deterrence position is that nuclear proliferation can be desirable. In this case, it is argued that, unlike conventional weapons, nuclear weapons deter all-out war between states, and they succeeded in doing this during the Cold War between the U.S. and the Soviet Union.[26] In the late 1950s and early 1960s, Gen. Pierre Marie Gallois of France, an adviser to Charles de Gaulle, argued in books like The Balance of Terror: Strategy for the Nuclear Age (1961) that mere possession of a nuclear arsenal was enough to ensure deterrence, and thus concluded that the spread of nuclear weapons could increase international stability. Some prominent neo-realist scholars, such as Kenneth Waltz and John Mearsheimer, have argued, along the lines of Gallois, that some forms of nuclear proliferation would decrease the likelihood of total war, especially in troubled regions of the world where there exists a single nuclear-weapon state. Aside from the public opinion that opposes proliferation in any form, there are two schools of thought on the matter: those, like Mearsheimer, who favored selective proliferation,[27] and Waltz, who was somewhat more non-interventionist.[28][29] Interest in proliferation and the stability-instability paradox that it generates continues to this day, with ongoing debate about indigenous Japanese and South Korean nuclear deterrent against North Korea.[30] The threat of potentially suicidal terrorists possessing nuclear weapons (a form of nuclear terrorism) complicates the decision process. The prospect of mutually assured destruction might not deter an enemy who expects to die in the confrontation. Further, if the initial act is from a stateless terrorist instead of a sovereign nation, there might not be a nation or specific target to retaliate against. It has been argued, especially after the September 11, 2001, attacks, that this complication calls for a new nuclear strategy, one that is distinct from that which gave relative stability during the Cold War.[31] Since 1996, the United States has had a policy of allowing the targeting of its nuclear weapons at terrorists armed with weapons of mass destruction.[32] A Minuteman III ICBM test launch from Vandenberg Air Force Base, United States. MIRVed land-based ICBMs are considered destabilizing because they tend to put a premium on striking first. Robert Gallucci argues that although traditional deterrence is not an effective approach toward terrorist groups bent on causing a nuclear catastrophe, Gallucci believes that "the United States should instead consider a policy of expanded deterrence, which focuses not solely on the would-be nuclear terrorists but on those states that may deliberately transfer or inadvertently leak nuclear weapons and materials to them. By threatening retaliation against those states, the United States may be able to deter that which it cannot physically prevent.".[33] Graham Allison makes a similar case, arguing that the key to expanded deterrence is coming up with ways of tracing nuclear material to the country that forged the fissile material. "After a nuclear bomb detonates, nuclear forensics cops would collect debris samples and send them to a laboratory for radiological analysis. By identifying unique attributes of the fissile material, including its impurities and contaminants, one could trace the path back to its origin."[34] The process is analogous to identifying a criminal by fingerprints. "The goal would be twofold: first, to deter leaders of nuclear states from selling weapons to terrorists by holding them accountable for any use of their weapons; second, to give leaders every incentive to tightly secure their nuclear weapons and materials."[34] According to the Pentagon's June 2019 "Doctrine for Joint Nuclear Operations" of the Joint Chiefs of Staffs website Publication, "Integration of nuclear weapons employment with conventional and special operations forces is essential to the success of any mission or operation."[35][36] Governance, control, and law Main articles: Treaty on the Non-Proliferation of Nuclear Weapons, Strategic Arms Limitation Talks, Intermediate-Range Nuclear Forces Treaty, START I, START II, Strategic Offensive Reductions Treaty, Comprehensive Nuclear-Test-Ban Treaty, Lahore Declaration, and New START See also: Anti-nuclear movement The International Atomic Energy Agency was created in 1957 to encourage peaceful development of nuclear technology while providing international safeguards against nuclear proliferation. Because they are weapons of mass destruction, the proliferation and possible use of nuclear weapons are important issues in international relations and diplomacy. In most countries, the use of nuclear force can only be authorized by the head of government or head of state.[c] Despite controls and regulations governing nuclear weapons, there is an inherent danger of "accidents, mistakes, false alarms, blackmail, theft, and sabotage".[37] In the late 1940s, lack of mutual trust prevented the United States and the Soviet Union from making progress on arms control agreements. The Russell–Einstein Manifesto was issued in London on July 9, 1955, by Bertrand Russell in the midst of the Cold War. It highlighted the dangers posed by nuclear weapons and called for world leaders to seek peaceful resolutions to international conflict. The signatories included eleven pre-eminent intellectuals and scientists, including Albert Einstein, who signed it just days before his death on April 18, 1955. A few days after the release, philanthropist Cyrus S. Eaton offered to sponsor a conference—called for in the manifesto—in Pugwash, Nova Scotia, Eaton's birthplace. This conference was to be the first of the Pugwash Conferences on Science and World Affairs, held in July 1957. By the 1960s, steps were taken to limit both the proliferation of nuclear weapons to other countries and the environmental effects of nuclear testing. The Partial Nuclear Test Ban Treaty (1963) restricted all nuclear testing to underground nuclear testing, to prevent contamination from nuclear fallout, whereas the Treaty on the Non-Proliferation of Nuclear Weapons (1968) attempted to place restrictions on the types of activities signatories could participate in, with the goal of allowing the transference of non-military nuclear technology to member countries without fear of proliferation. UN vote on adoption of the Treaty on the Prohibition of Nuclear Weapons on July 7, 2017   Yes   No   Did not vote In 1957, the International Atomic Energy Agency (IAEA) was established under the mandate of the United Nations to encourage development of peaceful applications of nuclear technology, provide international safeguards against its misuse, and facilitate the application of safety measures in its use. In 1996, many nations signed the Comprehensive Nuclear-Test-Ban Treaty,[38] which prohibits all testing of nuclear weapons. A testing ban imposes a significant hindrance to nuclear arms development by any complying country.[39] The Treaty requires the ratification by 44 specific states before it can go into force; as of 2012, the ratification of eight of these states is still required.[38] Additional treaties and agreements have governed nuclear weapons stockpiles between the countries with the two largest stockpiles, the United States and the Soviet Union, and later between the United States and Russia. These include treaties such as SALT II (never ratified), START I (expired), INF, START II (never in effect), SORT, and New START, as well as non-binding agreements such as SALT I and the Presidential Nuclear Initiatives[40] of 1991. Even when they did not enter into force, these agreements helped limit and later reduce the numbers and types of nuclear weapons between the United States and the Soviet Union/Russia. Nuclear weapons have also been opposed by agreements between countries. Many nations have been declared Nuclear-Weapon-Free Zones, areas where nuclear weapons production and deployment are prohibited, through the use of treaties. The Treaty of Tlatelolco (1967) prohibited any production or deployment of nuclear weapons in Latin America and the Caribbean, and the Treaty of Pelindaba (1964) prohibits nuclear weapons in many African countries. As recently as 2006 a Central Asian Nuclear Weapon Free Zone was established among the former Soviet republics of Central Asia prohibiting nuclear weapons. Large stockpile with global range (dark blue), smaller stockpile with global range (medium blue), small stockpile with regional range (light blue). In 1996, the International Court of Justice, the highest court of the United Nations, issued an Advisory Opinion concerned with the "Legality of the Threat or Use of Nuclear Weapons". The court ruled that the use or threat of use of nuclear weapons would violate various articles of international law, including the Geneva Conventions, the Hague Conventions, the UN Charter, and the Universal Declaration of Human Rights. Given the unique, destructive characteristics of nuclear weapons, the International Committee of the Red Cross calls on States to ensure that these weapons are never used, irrespective of whether they consider them lawful or not.[41] Additionally, there have been other, specific actions meant to discourage countries from developing nuclear arms. In the wake of the tests by India and Pakistan in 1998, economic sanctions were (temporarily) levied against both countries, though neither were signatories with the Nuclear Non-Proliferation Treaty. One of the stated casus belli for the initiation of the 2003 Iraq War was an accusation by the United States that Iraq was actively pursuing nuclear arms (though this was soon discovered not to be the case as the program had been discontinued). In 1981, Israel had bombed a nuclear reactor being constructed in Osirak, Iraq, in what it called an attempt to halt Iraq's previous nuclear arms ambitions; in 2007, Israel bombed another reactor being constructed in Syria. In 2013, Mark Diesendorf said that governments of France, India, North Korea, Pakistan, UK, and South Africa have used nuclear power and/or research reactors to assist nuclear weapons development or to contribute to their supplies of nuclear explosives from military reactors.[42] The two tied-for-lowest points for the Doomsday Clock have been in 1953, when the Clock was set to two minutes until midnight after the U.S. and the Soviet Union began testing hydrogen bombs, and in 2018, following the failure of world leaders to address tensions relating to nuclear weapons and climate change issues.[43] Disarmament Main article: Nuclear disarmament For statistics on possession and deployment, see List of states with nuclear weapons. The USSR and United States nuclear weapon stockpiles throughout the Cold War until 2015, with a precipitous drop in total numbers following the end of the Cold War in 1991. Nuclear disarmament refers to both the act of reducing or eliminating nuclear weapons and to the end state of a nuclear-free world, in which nuclear weapons are eliminated. Beginning with the 1963 Partial Test Ban Treaty and continuing through the 1996 Comprehensive Nuclear-Test-Ban Treaty, there have been many treaties to limit or reduce nuclear weapons testing and stockpiles. The 1968 Nuclear Non-Proliferation Treaty has as one of its explicit conditions that all signatories must "pursue negotiations in good faith" towards the long-term goal of "complete disarmament". The nuclear-weapon states have largely treated that aspect of the agreement as "decorative" and without force.[44] Only one country—South Africa—has ever fully renounced nuclear weapons they had independently developed. The former Soviet republics of Belarus, Kazakhstan, and Ukraine returned Soviet nuclear arms stationed in their countries to Russia after the collapse of the USSR. Proponents of nuclear disarmament say that it would lessen the probability of nuclear war, especially accidentally. Critics of nuclear disarmament say that it would undermine the present nuclear peace and deterrence and would lead to increased global instability. Various American elder statesmen,[45] who were in office during the Cold War period, have been advocating the elimination of nuclear weapons. These officials include Henry Kissinger, George Shultz, Sam Nunn, and William Perry. In January 2010, Lawrence M. Krauss stated that "no issue carries more importance to the long-term health and security of humanity than the effort to reduce, and perhaps one day, rid the world of nuclear weapons".[46] Ukrainian workers use equipment provided by the U.S. Defense Threat Reduction Agency to dismantle a Soviet-era missile silo. After the end of the Cold War, Ukraine and the other non-Russian, post-Soviet republics relinquished Soviet nuclear stockpiles to Russia. In January 1986, Soviet leader Mikhail Gorbachev publicly proposed a three-stage program for abolishing the world's nuclear weapons by the end of the 20th century.[47] In the years after the end of the Cold War, there have been numerous campaigns to urge the abolition of nuclear weapons, such as that organized by the Global Zero movement, and the goal of a "world without nuclear weapons" was advocated by United States President Barack Obama in an April 2009 speech in Prague.[48] A CNN poll from April 2010 indicated that the American public was nearly evenly split on the issue.[49] Some analysts have argued that nuclear weapons have made the world relatively safer, with peace through deterrence and through the stability–instability paradox, including in south Asia.[50][51] Kenneth Waltz has argued that nuclear weapons have helped keep an uneasy peace, and further nuclear weapon proliferation might even help avoid the large scale conventional wars that were so common before their invention at the end of World War II.[29] But former Secretary Henry Kissinger says there is a new danger, which cannot be addressed by deterrence: "The classical notion of deterrence was that there was some consequences before which aggressors and evildoers would recoil. In a world of suicide bombers, that calculation doesn't operate in any comparable way".[52] George Shultz has said, "If you think of the people who are doing suicide attacks, and people like that get a nuclear weapon, they are almost by definition not deterrable".[53] As of early 2019, more than 90% of world's 13,865 nuclear weapons were owned by Russia and the United States.[54][55] United Nations Main article: United Nations Office for Disarmament Affairs The UN Office for Disarmament Affairs (UNODA) is a department of the United Nations Secretariat established in January 1998 as part of the United Nations Secretary-General Kofi Annan's plan to reform the UN as presented in his report to the General Assembly in July 1997.[56] Its goal is to promote nuclear disarmament and non-proliferation and the strengthening of the disarmament regimes in respect to other weapons of mass destruction, chemical and biological weapons. It also promotes disarmament efforts in the area of conventional weapons, especially land mines and small arms, which are often the weapons of choice in contemporary conflicts. Controversy See also: Nuclear weapons debate and History of the anti-nuclear movement Ethics Main article: Nuclear ethics Anti-nuclear weapons protest march in Oxford, 1980 Even before the first nuclear weapons had been developed, scientists involved with the Manhattan Project were divided over the use of the weapon. The role of the two atomic bombings of the country in Japan's surrender and the U.S.'s ethical justification for them has been the subject of scholarly and popular debate for decades. The question of whether nations should have nuclear weapons, or test them, has been continually and nearly universally controversial.[57] Notable nuclear weapons accidents Main articles: Nuclear and radiation accidents and incidents and List of military nuclear accidents See also: List of nuclear close calls August 21, 1945: While conducting experiments on a plutonium-gallium core at Los Alamos National Laboratory, physicist Harry Daghlian received a lethal dose of radiation when an error caused it to enter prompt criticality. He died 25 days later, on September 15, 1945, from radiation poisoning. May 21, 1946: While conducting further experiments on the same core at Los Alamos National Laboratory, physicist Louis Slotin accidentally caused the core to become briefly supercritical. He received a lethal dose of gamma and neutron radiation, and died nine days later on May 30, 1946. After the death of Daghlian and Slotin, the mass became known as the "demon core". It was ultimately used to construct a bomb for use on the Nevada Test Range.[58] February 13, 1950: a Convair B-36B crashed in northern British Columbia after jettisoning a Mark IV atomic bomb. This was the first such nuclear weapon loss in history. The accident was designated a "Broken Arrow"—an accident involving a nuclear weapon but which does not present a risk of war. Experts believe that up to 50 nuclear weapons were lost during the Cold War.[59] May 22, 1957: a 42,000-pound (19,000 kg) Mark-17 hydrogen bomb accidentally fell from a bomber near Albuquerque, New Mexico. The detonation of the device's conventional explosives destroyed it on impact and formed a crater 25 feet (7.6 m) in diameter on land owned by the University of New Mexico. According to a researcher at the Natural Resources Defense Council, it was one of the most powerful bombs made to date.[60] June 7, 1960: the 1960 Fort Dix IM-99 accident destroyed a Boeing CIM-10 Bomarc nuclear missile and shelter and contaminated the BOMARC Missile Accident Site in New Jersey. January 24, 1961: the 1961 Goldsboro B-52 crash occurred near Goldsboro, North Carolina. A Boeing B-52 Stratofortress carrying two Mark 39 nuclear bombs broke up in mid-air, dropping its nuclear payload in the process.[61] 1965 Philippine Sea A-4 crash, where a Skyhawk attack aircraft with a nuclear weapon fell into the sea.[62] The pilot, the aircraft, and the B43 nuclear bomb were never recovered.[63] It was not until 1989 that the Pentagon revealed the loss of the one-megaton bomb.[64] January 17, 1966: the 1966 Palomares B-52 crash occurred when a B-52G bomber of the USAF collided with a KC-135 tanker during mid-air refuelling off the coast of Spain. The KC-135 was completely destroyed when its fuel load ignited, killing all four crew members. The B-52G broke apart, killing three of the seven crew members aboard.[65] Of the four Mk28 type hydrogen bombs the B-52G carried,[66] three were found on land near Almería, Spain. The non-nuclear explosives in two of the weapons detonated upon impact with the ground, resulting in the contamination of a 2-square-kilometer (490-acre) (0.78 square mile) area by radioactive plutonium. The fourth, which fell into the Mediterranean Sea, was recovered intact after a 21⁄2-month-long search.[67] January 21, 1968: the 1968 Thule Air Base B-52 crash involved a United States Air Force (USAF) B-52 bomber. The aircraft was carrying four hydrogen bombs when a cabin fire forced the crew to abandon the aircraft. Six crew members ejected safely, but one who did not have an ejection seat was killed while trying to bail out. The bomber crashed onto sea ice in Greenland, causing the nuclear payload to rupture and disperse, which resulted in widespread radioactive contamination.[68] One of the bombs remains lost.[69] September 18–19, 1980: the Damascus Accident, occurred in Damascus, Arkansas, where a Titan missile equipped with a nuclear warhead exploded. The accident was caused by a maintenance man who dropped a socket from a socket wrench down an 80-foot (24 m) shaft, puncturing a fuel tank on the rocket. Leaking fuel resulted in a hypergolic fuel explosion, jettisoning the W-53 warhead beyond the launch site.[70][71][72] Nuclear testing and fallout Main article: Nuclear fallout See also: Downwinders Over 2,000 nuclear tests have been conducted in over a dozen different sites around the world. Red Russia/Soviet Union, blue France, light blue United States, violet Britain, yellow China, orange India, brown Pakistan, green North Korea and light green (territories exposed to nuclear bombs). The Black dot indicates the location of the Vela incident. This view of downtown Las Vegas shows a mushroom cloud in the background. Scenes such as this were typical during the 1950s. From 1951 to 1962 the government conducted 100 atmospheric tests at the nearby Nevada Test Site. Over 500 atmospheric nuclear weapons tests were conducted at various sites around the world from 1945 to 1980. Radioactive fallout from nuclear weapons testing was first drawn to public attention in 1954 when the Castle Bravo hydrogen bomb test at the Pacific Proving Grounds contaminated the crew and catch of the Japanese fishing boat Lucky Dragon.[73] One of the fishermen died in Japan seven months later, and the fear of contaminated tuna led to a temporary boycotting of the popular staple in Japan. The incident caused widespread concern around the world, especially regarding the effects of nuclear fallout and atmospheric nuclear testing, and "provided a decisive impetus for the emergence of the anti-nuclear weapons movement in many countries".[73] As public awareness and concern mounted over the possible health hazards associated with exposure to the nuclear fallout, various studies were done to assess the extent of the hazard. A Centers for Disease Control and Prevention/ National Cancer Institute study claims that fallout from atmospheric nuclear tests would lead to perhaps 11,000 excess deaths among people alive during atmospheric testing in the United States from all forms of cancer, including leukemia, from 1951 to well into the 21st century.[74][75] As of March 2009, the U.S. is the only nation that compensates nuclear test victims. Since the Radiation Exposure Compensation Act of 1990, more than $1.38 billion in compensation has been approved. The money is going to people who took part in the tests, notably at the Nevada Test Site, and to others exposed to the radiation.[76][77] In addition, leakage of byproducts of nuclear weapon production into groundwater has been an ongoing issue, particularly at the Hanford site.[78] Effects of nuclear explosions Main article: Effects of nuclear explosions Effects of nuclear explosions on human health Main article: Effects of nuclear explosions on human health A photograph of Sumiteru Taniguchi's back injuries taken in January 1946 by a U.S. Marine photographer Some scientists estimate that a nuclear war with 100 Hiroshima-size nuclear explosions on cities could cost the lives of tens of millions of people from long-term climatic effects alone. The climatology hypothesis is that if each city firestorms, a great deal of soot could be thrown up into the atmosphere which could blanket the earth, cutting out sunlight for years on end, causing the disruption of food chains, in what is termed a nuclear winter.[79][80] People near the Hiroshima explosion and who managed to survive the explosion subsequently suffered a variety of medical effects:[81] Initial stage—the first 1–9 weeks, in which are the greatest number of deaths, with 90% due to thermal injury and/or blast effects and 10% due to super-lethal radiation exposure. Intermediate stage—from 10 to 12 weeks. The deaths in this period are from ionizing radiation in the median lethal range – LD50 Late period—lasting from 13 to 20 weeks. This period has some improvement in survivors' condition. Delayed period—from 20+ weeks. Characterized by numerous complications, mostly related to healing of thermal and mechanical injuries, and if the individual was exposed to a few hundred to a thousand millisieverts of radiation, it is coupled with infertility, sub-fertility and blood disorders. Furthermore, ionizing radiation above a dose of around 50–100 millisievert exposure has been shown to statistically begin increasing one's chance of dying of cancer sometime in their lifetime over the normal unexposed rate of ~25%, in the long term, a heightened rate of cancer, proportional to the dose received, would begin to be observed after ~5+ years, with lesser problems such as eye cataracts and other more minor effects in other organs and tissue also being observed over the long term. Fallout exposure—depending on if further afield individuals shelter in place or evacuate perpendicular to the direction of the wind, and therefore avoid contact with the fallout plume, and stay there for the days and weeks after the nuclear explosion, their exposure to fallout, and therefore their total dose, will vary. With those who do shelter in place, and or evacuate, experiencing a total dose that would be negligible in comparison to someone who just went about their life as normal.[82][83] Staying indoors until after the most hazardous fallout isotope, I-131 decays away to 0.1% of its initial quantity after ten half-lifes—which is represented by 80 days in I-131s case, would make the difference between likely contracting Thyroid cancer or escaping completely from this substance depending on the actions of the individual.[84] Effects of nuclear war See also: Nuclear holocaust, Doomsday Clock, Doomsday device, World War III, and Nuclear famine Mushroom cloud from the explosion of Castle Bravo, the largest nuclear weapon detonated by the U.S., in 1954 Nuclear war could yield unprecedented human death tolls and habitat destruction. Detonating large numbers of nuclear weapons would have an immediate, short term and long-term effects on the climate, potentially causing cold weather known as a "nuclear winter".[85][86] In 1982, Brian Martin estimated that a US–Soviet nuclear exchange might kill 400–450 million directly, mostly in the United States, Europe and Russia, and maybe several hundred million more through follow-up consequences in those same areas.[87] Many scholars have posited that a global thermonuclear war with Cold War-era stockpiles, or even with the current smaller stockpiles, may lead to the extinction of the human race.[88] The International Physicians for the Prevention of Nuclear War believe that nuclear war could indirectly contribute to human extinction via secondary effects, including environmental consequences, societal breakdown, and economic collapse. It has been estimated that a relatively small-scale nuclear exchange between India and Pakistan involving 100 Hiroshima yield (15 kilotons) weapons, could cause a nuclear winter and kill more than a billion people.[89] According to a peer-reviewed study published in the journal Nature Food in August 2022, a full-scale nuclear war between the U.S. and Russia would directly kill 360 million people and more than 5 billion people would die from starvation. More than 2 billion people could die from a smaller-scale nuclear war between India and Pakistan.[86][90][91] Public opposition See also: Nuclear disarmament and International Day against Nuclear Tests Protest in Bonn against the nuclear arms race between the U.S./NATO and the Warsaw Pact, 1981 Demonstration against nuclear testing in Lyon, France, in the 1980s. Peace movements emerged in Japan and in 1954 they converged to form a unified "Japan Council against Atomic and Hydrogen Bombs." Japanese opposition to nuclear weapons tests in the Pacific Ocean was widespread, and "an estimated 35 million signatures were collected on petitions calling for bans on nuclear weapons".[92] In the United Kingdom, the first Aldermaston March organised by the Campaign for Nuclear Disarmament(CND) took place at Easter 1958, when, according to the CND, several thousand people marched for four days from Trafalgar Square, London, to the Atomic Weapons Research Establishment close to Aldermaston in Berkshire, England, to demonstrate their opposition to nuclear weapons.[93][94] The Aldermaston marches continued into the late 1960s when tens of thousands of people took part in the four-day marches.[92] In 1959, a letter in the Bulletin of the Atomic Scientists was the start of a successful campaign to stop the Atomic Energy Commission dumping radioactive waste in the sea 19 kilometres from Boston.[95] In 1962, Linus Pauling won the Nobel Peace Prize for his work to stop the atmospheric testing of nuclear weapons, and the "Ban the Bomb" movement spread.[57] In 1963, many countries ratified the Partial Test Ban Treaty prohibiting atmospheric nuclear testing. Radioactive fallout became less of an issue and the anti-nuclear weapons movement went into decline for some years.[73][96] A resurgence of interest occurred amid European and American fears of nuclear war in the 1980s.[97] Costs and technology spin-offs See also: Global Positioning System, Nuclear weapons delivery, History of computing hardware, ENIAC, and Swords to ploughshares According to an audit by the Brookings Institution, between 1940 and 1996, the U.S. spent $10.9 trillion in present-day terms[98] on nuclear weapons programs. 57% of which was spent on building nuclear weapons delivery systems. 6.3% of the total, $681 billion in present-day terms, was spent on environmental remediation and nuclear waste management, for example cleaning up the Hanford site, and 7% of the total, $763 billion was spent on making nuclear weapons themselves.[99] Non-weapons uses Main article: Peaceful nuclear explosion Peaceful nuclear explosions are nuclear explosions conducted for non-military purposes, such as activities related to economic development including the creation of canals. During the 1960s and 1970s, both the United States and the Soviet Union conducted a number of PNEs. Six of the explosions by the Soviet Union are considered to have been of an applied nature, not just tests. The United States and the Soviet Union later halted their programs. Definitions and limits are covered in the Peaceful Nuclear Explosions Treaty of 1976.[100][101] The stalled Comprehensive Nuclear-Test-Ban Treaty of 1996 would prohibit all nuclear explosions, regardless of whether they are for peaceful purposes or not.[102] History of development Main article: History of nuclear weapons See also: Soviet atomic bomb project, Manhattan Project, Cold War, and History of the Teller–Ulam design This section is an excerpt from History of nuclear weapons § Background.[edit] In nuclear fission, the nucleus of a fissile atom (in this case, enriched uranium) absorbs a thermal neutron, becomes unstable and splits into two new atoms, releasing some energy and between one and three new neutrons, which can perpetuate the process. In the first decades of the 20th century, physics was revolutionized with developments in the understanding of the nature of atoms including the discoveries in atomic theory by John Dalton.[103] In 1898, Pierre and Marie Curie discovered that pitchblende, an ore of uranium, contained a substance—which they named radium—that emitted large amounts of radiation. Ernest Rutherford and Frederick Soddy identified that atoms were breaking down and turning into different elements. Hopes were raised among scientists and laymen that the elements around us could contain tremendous amounts of unseen energy, waiting to be harnessed. In Paris in 1934, Irène and Frédéric Joliot-Curie discovered that artificial radioactivity could be induced in stable elements by bombarding them with alpha particles; in Italy Enrico Fermi reported similar results when bombarding uranium with neutrons. In December 1938, Otto Hahn and Fritz Strassmann reported that they had detected the element barium after bombarding uranium with neutrons. Lise Meitner and Otto Robert Frisch correctly interpreted these results as being due to the splitting of the uranium atom. Frisch confirmed this experimentally on January 13, 1939.[104] They gave the process the name "fission" because of its similarity to the splitting of a cell into two new cells. Even before it was published, news of Meitner's and Frisch's interpretation crossed the Atlantic.[105] In their second publication on nuclear fission in February of 1939, Hahn and Strassmann predicted the existence and liberation of additional neutrons during the fission process, opening up the possibility of a nuclear chain reaction. After learning about the German fission in 1939, Szilard concluded that uranium would be the element which can realize his 1933 idea about nuclear chain reaction.[106] Uranium appears in nature primarily in two isotopes: uranium-238 and uranium-235. When the nucleus of uranium-235 absorbs a neutron, it undergoes nuclear fission, releasing energy and, on average, 2.5 neutrons. Because uranium-235 releases more neutrons than it absorbs, it can support a chain reaction and so is described as fissile. Uranium-238, on the other hand, is not fissile as it does not normally undergo fission when it absorbs a neutron. By the start of the war in September 1939, many scientists likely to be persecuted by the Nazis had already escaped. Physicists on both sides were well aware of the possibility of utilizing nuclear fission as a weapon, but no one was quite sure how it could be engineered. In August 1939, concerned that Germany might have its own project to develop fission-based weapons, Albert Einstein signed a letter to U.S. President Franklin D. Roosevelt warning him of the threat.[107] Major General Leslie Groves and Robert Oppenheimer at the Trinity test site in 1945 Roosevelt responded by setting up the Uranium Committee under Lyman James Briggs but, with little initial funding ($6,000), progress was slow. It was not until the U.S. entered the war in December 1941 that Washington decided to commit the necessary resources to a top-secret high priority bomb project.[108] Organized research first began in Britain and Canada as part of the Tube Alloys project: the world's first nuclear weapons project. The Maud Committee was set up following the work of Frisch and Rudolf Peierls who calculated uranium-235's critical mass and found it to be much smaller than previously thought which meant that a deliverable bomb should be possible.[109] In the February 1940 Frisch–Peierls memorandum they stated that: "The energy liberated in the explosion of such a super-bomb...will, for an instant, produce a temperature comparable to that of the interior of the sun. The blast from such an explosion would destroy life in a wide area. The size of this area is difficult to estimate, but it will probably cover the centre of a big city." Edgar Sengier, a director of Shinkolobwe Mine in the Congo which produced by far the highest quality uranium ore in the world, had become aware of uranium's possible use in a bomb. In late 1940, fearing that it might be seized by the Germans, he shipped the mine's entire stockpile of ore to a warehouse in New York.[110] Leo Szilard, invented the electron microscope, linear accelerator, cyclotron, nuclear chain reaction and patented the nuclear reactor in London in 1934. See also Cobalt bomb Cosmic bomb (phrase) Cuban Missile Crisis Dirty bomb Induced gamma emission List of states with nuclear weapons List of nuclear close calls List of nuclear weapons Nth Country Experiment Nuclear blackout Nuclear bunker buster Nuclear holocaust Nuclear weapons of the United Kingdom Nuclear weapons in popular culture Nuclear weapons of the United States OPANAL (Agency for the Prohibition of Nuclear Weapons in Latin America and the Caribbean) Three Non-Nuclear Principles of Japan J. Robert Oppenheimer (1904-1967) was an American theoretical physicist.  During the Manhattan Project, Oppenheimer was director of the Los Alamos Laboratory and responsible for the research and design of an atomic bomb. He is often known as the “father of the atomic bomb.” By the time the Manhattan Project was launched in the fall of 1942, Oppenheimer was already considered an exceptional theoretical physicist and had become deeply involved in exploring the possibility of an atomic bomb. Throughout the previous year he had been doing research on fast neutrons, calculating how much material might be needed for a bomb and how efficient it might be.  Although Oppenheimer had little managerial experience and some troublesome past associations with Communist causes, General Leslie Groves recognized his exceptional scientific brilliance. Less than three years after Groves selected Oppenheimer to direct weapons development, the United States dropped two atomic bombs on Japan. As director of the Los Alamos Laboratory, Oppenheimer proved to be an extraordinary choice. Oppenheimer was married to a botanist, Kitty. They had two children, Peter and Toni.   Early Life Oppenheimer was born on April 22, 1904. Oppenheimer’s family was part of the Ethical Culture Society, an outgrowth of American Reform Judaism founded and led at the time by Dr. Felix Adler. The progressive society placed an emphasis on social justice, civic responsibility, and secular humanism. Dr. Adler also founded the Ethical Culture School, where Oppenheimer enrolled in September 1911. His academic prowess was apparent very early on, and by the age of 10, Oppenheimer was studying minerals, physics, and chemistry. His correspondence with the New York Mineralogical Club was so advanced that the Society invited him to deliver a lecture—not realizing that Robert was a twelve-year-old boy. He graduated as valedictorian of his high school class in 1921, but fell ill with a near-fatal case of dysentery and was forced to postpone enrolling at Harvard. After being bedridden for months, his parents arranged for him to spend the summer of 1922 in New Mexico, a haven for health-seekers. Robert stayed at a dude ranch 25 miles northeast of Santa Fe with high school teacher Herbert Smith as a companion and mentor. From there, he took five- or six-day horseback trips in the wilderness. This experience restored Oppenheimer’s health and instilled a deep love for the desert high country. Oppenheimer enrolled at Harvard in September 1922. He graduated in three years, excelling in a wide variety of subjects. Although he majored in chemistry, Oppenheimer eventually realized his true passion was the study of physics. In 1925, Oppenheimer began his graduate work in physics at Cavendish Laboratory in Cambridge, England. J. J. Thomson, who had been awarded the 1906 Nobel Prize in Physics for detecting the electron, agreed to take on Oppenheimer as a student. At Cavendish, Oppenheimer realized that his talent was for theoretical, not experimental, physics, and he accepted an invitation from Max Born, director of the Institute of Theoretical Physics at the University of Göttingen, to study with him in Germany. Oppenheimer had the good fortune to be in Europe during a pivotal time in the world of physics, as European physicists were then developing the groundbreaking theory of quantum mechanics. Oppenheimer received his doctorate in 1927 and accepted professorships at the University of California, Berkeley, and the California Institute of Technology. At Berkeley, he became good friends with Ernest Lawrence, one of the world’s top experimental physicists and the inventor of the cyclotron. Lawrence named his second son after Robert.   Later Years After the war Oppenheimer became an advisor of the Atomic Energy Commission, lobbying for international arms control. Beginning in 1947, Oppenheimer directed the Institute for Advanced Study in Princeton, New Jersey, where he convened great scientists. “What we don’t understand, we explain to each other.”  His security clearance was revoked in 1954 in a hearing during the Second Red Scare. Oppenheimer’s old Communist sympathies were dredged up and his clearance was revoked a mere 32 hours before it was set to expire. Oppenheimer had made political enemies by arguing against the development of the hydrogen bomb, and revoking his clearance stripped him of political power. The scientific community was outraged at the treatment of Oppenheimer, and reviled Edward Teller, who testified against him at the hearing. For more information, please see Oppenheimer Security Hearing. Along with Albert Einstein, Bertrand Russell, and Joseph Rotblat he established the World Academy of Art and Science in 1960. He continued lecturing around the world, and was awarded the Enrico Fermi Award in 1963. He died of throat cancer in 1967. J. Robert Oppenheimer's Timeline 1904 Apr 22nd Born in New York, New York. 1911 Sep Enrolled in the Ethical Cultural School in New York City. 1921 Graduated as valedictorian of his high school class. 1922 After being bedridden with dysentery, spent the summer in New Mexico to recuperate. 1922 Enrolled at Harvard University. 1925 Began graduate work in physics at Cavendish Laboratory in Cambridge, England under J. J. Thomson. 1926 Moved from Cavendish Laboratory to the University of Göttingen to finish his graduate studies under Max Born. 1927 Received Ph.D. in Physics from the University of Göttingen. 1927 Joined the faculty at the University of California, Berkeley, and Caltech. 1942 Jan Organized a program on fast neutron theoretical physics at the University of California at Berkeley. 1942 Jun Joined the Chicago Met Lab to lead an effort on fast neutron physics, and prepared an outline for the entire neutron physics program. 1942 Jul1942 Sep Assembled theoretical study group in Berkeley to examine the principles of bomb design. Emerged as the natural leader. 1942 Sep 29th Proposed that a "fast-neutron lab" to study fast neutron physics and develop designs for an atomic bomb be created. 1942 Oct 15th General Leslie R. Groves asked J. Robert Oppenheimer to head Project Y, planned to be the new central laboratory for weapon physics research and design. 1942 Oct 19th Vannevar Bush approves Oppenheimer's appointment in meeting with Oppenheimer and General Groves. 1942 Nov 16th General Groves and Oppenheimer visit the Los Alamos, NM mesa in New Mexico and select it for "Site Y. 19431945 Director of the Los Alamos Laboratory. 1945 Jul 16th To his immense relief, witnessed the successful Trinity test. 1945 Oct 16th Resigns as director of Los Alamos Laboratory, accepting a post at CalTech. 1947 Became director of the Institute for Advanced Study in Princeton, New Jersey. 1954 Jun 29th Oppenheimer's security clearance was revoked by the US Atomic Energy Commission, just 32 hours before it was set to expire. 1963 Dec 2nd Received the Enrico Fermi Award. 1967 Feb 18th Died in Princeton, New Jersey. J. (Julius) Robert Oppenheimer was born in New York City on April 22, 1904. His parents, Julius S. Oppenheimer, a wealthy German textile merchant, and Ella Friedman, an artist, were of Jewish descent but did not observe the religious traditions. He studied at the Ethical Culture Society School, whose physics laboratory has since been named for him, and entered Harvard in 1922, intending to become a chemist, but soon switching to physics. He graduated summa cum laude in 1925 and went to England to conduct research at Cambridge University's Cavendish Laboratory, working under J.J. Thomson. In 1926, Oppenheimer went to the University of Göttingen to study under Max Born, obtaining his Ph.D. at the age of 22. There, he published many important contributions to the then newly developed quantum theory, most notably a famous paper on the so-called Born-Oppenheimer approximation, which separates nuclear motion from electronic motion in the mathematical treatment of molecules. In 1927, he returned to Harvard to study mathematical physics and as a National Research Council Fellow, and in early 1928, he studied at the California Institute of Technology. He accepted an assistant professorship in physics at the University of California, Berkeley, and maintained a joint appointment with California Institute of Technology. In the ensuing 13 years, he "commuted" between the two universities, and many of his associates and students commuted with him. Oppenheimer became credited with being a founding father of the American school of theoretical physics. He did important research in astrophysics, nuclear physics, spectroscopy and quantum field theory. He made important contributions to the theory of cosmic ray showers, and did work that eventually led toward descriptions of quantum tunneling. In the 1930s, he was the first to write papers suggesting the existence of what we today call black holes. In November 1940, Oppenheimer married Katherine Peuning Harrison, a radical Berkeley student, and by May 1941 they had their first child, Peter. When World War II began, Oppenheimer eagerly became involved in the efforts to develop an atomic bomb, which were already taking up much of the time and facilities of Lawrence's Radiation Laboratory at Berkeley. He was invited to take over work on neutron calculations, and in June 1942 General Leslie Groves appointed Oppenheimer as the scientific director of the Manhattan Project. Under Oppenheimer's guidance, the laboratories at Los Alamos were constructed. There, he brought the best minds in physics to work on the problem of creating an atomic bomb. In the end, he was managing more than 3,000 people, as well as tackling theoretical and mechanical problems that arose. He is often referred to as the "father" of the atomic bomb. (In 1944, the Oppenheimers' second child, Katherine (called Toni), was born at Los Alamos.) The joint work of the scientists at Los Alamos resulted in the first nuclear explosion at Alamagordo on July 16, 1945, which Oppenheimer named "Trinity." After the war, Oppenheimer was appointed Chairman of the General Advisory Committee to the Atomic Energy Commission (AEC), serving from 1947 to 1952. It was in this role that he voiced strong opposition to the development of the hydrogen bomb. In 1953, at the height of U.S. anticommunist feeling, Oppenheimer was accused of having communist sympathies, and his security clearance was taken away. The scientific community, with few exceptions, was deeply shocked by the decision of the AEC. In 1963, President Lyndon B. Johnson attempted to redress these injustices by honoring Oppenheimer with the Atomic Energy Commission's prestigious Enrico Fermi Award. From 1947 to 1966, Oppenheimer also served as Director of Princeton's Institute for Advanced Study. There, he stimulated discussion and research on quantum and relativistic physics in the School of Natural Sciences. Oppenheimer retired from the Institute in 1966 and died of throat cancer on February 18, 1967.
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