Sir James Chadwick (20 October 1891 – 24 July 1974) was an English physicist who was awarded the Nobel Prize in physics for his 1932 discovery of the neutron. He later measured its mass.
Born in Bollington, he studied at the University of Manchester. His early research, under Hans Geiger, showed that beta radiation produces a continuous electromagnetic spectrum. He was Assistant Director, under Ernest Rutherford, of the University of Cambridge's Cavendish Laboratory for over a decade, when it was one of the world's foremost centres for physics research.
In 1935, Chadwick joined the University of Liverpool, turning its physics laboratory into an important nuclear physics research centre by installing a cyclotron. During the Second World War, he was involved in the Tube Alloys project to build an atomic bomb, and later led the British team working on the Manhattan Project. Knighted in 1945, he served as Master of Gonville and Caius College, Cambridge 1948–1958.