James Chadwick
1891–1974, Bollington, Cheshire, England, Cambridge, England
English physicist who discovered the neutron in 1932; he received the 1935 Nobel Prize in Physics.
Chadwick was born in Bollington, Cheshire, studied at the University of Manchester, then researched in Berlin under Hans Geiger — where he was interned during the First World War as an enemy civilian. From 1919 he worked with Rutherford at the Cavendish Laboratory in Cambridge, becoming assistant director of research.
At the Cavendish he discovered the neutron in 1932, then took the Lyon Jones chair at the University of Liverpool in 1935 and built Britain's first cyclotron. During the Second World War he headed the British mission to the Manhattan Project at Los Alamos and wrote the final MAUD Committee report asserting the feasibility of the atomic bomb.
Nobel-winning work
In February 1932, Chadwick identified the neutron — a neutral particle with roughly the proton's mass — by interpreting the recoil of protons and nuclei struck by a mysterious radiation emitted when beryllium was bombarded by polonium alpha particles. This radiation had been observed by Bothe and Becker and studied by the Joliot-Curies, but both pairs mistook it for high-energy gamma rays. Chadwick showed that only the hypothesis of a massive neutral particle was consistent with the measured recoil energies.
The neutron — conjectured by Rutherford as early as 1920 — immediately explained the nucleus as composed of protons and neutrons, made sense of isotopes, and became both the tool and the weapon of nuclear physics: within its reach lay fission. Chadwick received the 1935 Nobel Prize in Physics 'for the discovery of the neutron'.
Workplaces: University of Cambridge (Cavendish Laboratory), University of Liverpool, Los Alamos National Laboratory
United Kingdom