In October 1941 Oppenheimer began fast-neutron research for the U.S. government in connection with atomic bomb development. One year later he became director of the central laboratory for bomb design and development at Los Alamos, New Mexico, supervising the Manhattan Project. In this enormously demanding position he displayed new self-discipline, and his skillful intellectual leadership, capacity to absorb and process information, concern for the team of 1,500 working under him, and ability to negotiate the often-difficult relationship between individualistic scientists and governmental demands for conformity became legendary. After the 1945 atomic explosions over Hiroshima and Nagasaki, the exhausted Oppenheimer, who told President Harry S. Truman that "I feel we have blood on our hands," hoped that the bomb's destructiveness might eventually force nations to abandon war.
Leaving Los Alamos in late 1945, Oppenheimer became director of the Institute for Advanced Study at Princeton two years later and quickly transformed it into the world's leading center for theoretical physics while simultaneously enhancing its existing reputation in humanist studies. As the most prestigious American advisor to the 1945–1946 Acheson-Lilienthal Committee on Nuclear Power and the United States Atomic Energy Commission (AEC), he advocated international control of atomic energy and lectured extensively, seeking to enhance popular scientific understanding.
In 1953 growing domestic McCarthyist, anticommunist sentiment and resentment by some colleagues—notably Edward Teller—of Oppenheimer's earlier reluctance to develop a thermonuclear bomb led the American government to withdraw his security clearance. This was done on the grounds that his wartime evasiveness over potential security problems and prewar left-wing and communist associates, including his brother, a former fiancée, and his wife, had permanently compromised his status. A full-scale inquiry held in 1954 at Oppenheimer's insistence confirmed this verdict. Later evidence revealed that the Federal Bureau of Investigation (FBI) blatantly infringed Oppenheimer's civil rights by tapping his telephone and providing transcripts of his legal consultations to the inquiry's members. In 1994 retired Soviet spy General Pavel A. Sudoplatov claimed in his memoirs that Oppenheimer had passed atomic secrets to Soviet agents, but major errors in his account led most in the scientific community to doubt this. Although excluded from governmental counsels, Oppenheimer retained his academic position at Princeton until June 1966, publishing several books on science for the educated general reader. He died in Princeton, New Jersey, on 18 February 1967.
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