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JAMES CHADWICK
(Physicist and and Leader of the British Mission at Los Alamos, 1943-1945)
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James Chadwick was a Nobel Prize-winning physicist who headed the British Mission to the United States during the Manhattan Project. He was born in Manchester, England, on October 20, 1891. In 1913, following graduation from Manchester University, where he worked on various radioactivity problems under Ernest Rutherford, Chadwick traveled to Germany to study with Hans Geiger. Trapped in Germany when war erupted the following year, Chadwick spent the First World War interned in a civilian prisoner-of-war camp. In 1919, Chadwick accompanied Rutherford to Cambridge University when Rutherford replaced J. J. Thomson as director of the Cavendish Laboratory. Chadwick had long suspected the existence of a neutral particle in the nucleus of the atom, and in 1932 he succeeded in proving the existence of the neutron by bombarding the element beryllium with alpha particles. In 1935, he was awarded the Nobel Prize in physics for his discovery of the neutron. He left Cambridge for the University of Liverpool that same year. 
Following the discovery of fission by the Germans Otto Hahn and Fritz Strassmann in December 1938, Chadwick was consulted by British officials on the possibility of a chain reaction in uranium creating an explosion of unprecedented power. He cautiously replied that it might be possible but work needed to be done on cross sections, the probabilities of fission as a function of neutron energy. This he set out to do using his recently completed cyclotron. Chadwick also was on the official British committee on atomic bomb research, known as the MAUD Committee, which first convened on April 10, 1940. When research by the refugee physicists Rudolf Peierls and Otto Frisch indicated that an enormous explosion was possible with a relatively small mass of uranium-235 using fast neutrons, Chadwick confirmed the findings, embarrassedly confessing that he had not felt justified in reporting them until more was known about the neutron cross sections. Chadwick subsequently coordinated investigations into developing techniques for the separation of uranium-235. By Spring 1941, the MAUD Committee concluded that a bomb was feasible and that a practical method of producing uranium-235 could be developed. When cross section measurements in the United States confirmed his own, Chadwick noted that "a nuclear bomb was not only possible--it was inevitable." The MAUD findings were extremely influential in accelerating the American program in fall 1941. Exchange of information across the Atlantic continued into mid-1942. With the takeover of by the Army of the bomb project in the United States, however, the rigid security system severely curtailed information exchange. Not until August 1943, with the personal intervention of British Prime Minister Winston Churchill was collaboration restored. A Combined Policy Committee was set up, with Chadwick as senior technical adviser to the British members. The committee met in Washington for the first time in September and immediately set up a three-person subcommittee, with Chadwick as the British member. Chadwick realized that the duty of the British was to assist the ongoing American project and not attempt to set up a parallel project back home. He concluded that the best approach would be to send British scientists to work in the United States. In December, an agreement was reached on interchange. As head of the British Mission of scientists, Chadwick alone among his compatriots would have access to all American and British work on both research and plant scale. Accompanied by a small party of scientists, he would help direct experiments at the Los Alamos laboratory. Other British scientists would be involved with gaseous diffusion and electromagnetic separation research. After an initial stint at Los Alamos, Chadwick spent most of the rest of the war in Washington with diplomatic and administrative duties. While there, he formed a relationship of trust and understanding with General Leslie Groves, head of the Manhattan Project, that went a long way toward making interchange between the two nations successful. After the war, Chadwick returned to his position at the University of Liverpool. He was knighted in 1945 and continued to influence both government and scientific policy and activities. In 1948, he returned to Cambridge and retired ten years later. He died in 1974.
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The text for this page is original to the Department of Energy's Office of History and Heritage Resources. Major sources consulted include the following. Lillian Hoddeson, et. al., Critical Assembly: A Technical History of Los Alamos during the Oppenheimer Years, 1943-1945 (Cambridge: Cambridge University Press, 1993), 18, 22, 35-36, 98-99, 159, Chadwick quote on p. 22; Richard G. Hewlett and Jack M. Holl, Atoms for Peace and War, 1953-1961: Eisenhower and the Atomic Energy Commission (Berkeley: University of California Press, 1989), 12, 255-84; Maurice Goldhaber, "With Chadwick at the Cavendish," and Mark Oliphant, "The Beginning: Chadwick and the Neutron," both in The Bulletin of the Atomic Scientists 38, No. 10 (December 1982): 12-18; Dennis C. Fakley, "The British Mission," Los Alamos Science (Winter/Spring 1983), 186-89. See also Chadwick's biography and Nobel lecture at http://nobelprize.org/nobel_prizes/physics/laureates/1935/chadwick-bio.html and Margaret Gowing, Britain and Atomic Energy, 1939-1945 (London: Macmillan, 1964). The photograph of Chadwick with the pipe is courtesy the Department of Energy. The invitation to a British Mission party is reproduced from Dennis C. Fakley, "The British Mission," Los Alamos Science (Winter/Spring 1983), p. 189.