Sir James Chadwick (1891-1974) was an English physicist and winner of the 1935 Nobel Prize in Physics.
Chadwick was a member of the British MAUD Committee, which concluded that the creation of nuclear weapons was possible and even inevitable – a major factor in President Roosevelt's decision to build the atomic bomb. He visited the United States on the 1940 Tizard Mission in support of greater Anglo-American scientific cooperation on wartime technologies.
From 1943 to 1946, Chadwick was head of the British Mission to the Manhattan Project in Los Alamos and was the leading British scientist to advocate for British nuclear weapons. Chadwick was friendly with General Leslie Groves and supported strong British relations with the United States. He helped draft agreements to provide uranium for the Manhattan Project, maintained the morale of British scientists during their time in America, and was responsible for British observers being present at the bombing of Nagasaki.
Chadwick is best known for his discovery of the neutron in 1932. A neutron is a particle with no electric charge that, along with positively charged protons, makes up an atom's nucleus. Bombarding elements with neutrons can succeed in penetrating and splitting nuclei, generating an enormous amount of energy. In this way, Chadwick's findings were pivotal to the discovery of nuclear fission, and ultimately the development of the atomic bomb. For more on Chadwick's scientific contributions, please visit the Nobel Prize website.
Chadwick returned to England in 1946. He also served on the Advisory Committee on Atomic Energy and as the British scientific advisor to the United Nations Atomic Energy Commission.