James Chadwick was the British physicist who discovered the neutron. He began his research into radioactivity with Ernest Rutherford at Manchester and in 1913 moved to Berlin to gain further experience with Hans Geiger. There he was interned as an enemy alien during the First World War, but still managed to continue his research in the stable where he was forced to live. After the war he returned to Cambridge and began work again with Rutherford, who in 1920 suspected the existence of a neutral particle. In 1930, Walther Bothe observed that a high energy gamma-ray was emitted from beryllium when bombarded with alpha-particles. It was an experiment that Chadwick repeated and, after measuring the energies involved and noting the conservation of energy and momentum, he began to realize that a new particle was being produced rather than electromagnetic radiation. From a series of similar experiments using boron, Chadwick was able in 1932 to calculate the mass of this particle, showing it to be slightly greater than that of a proton. He named this particle the neutron and its existence was soon confirmed elsewhere (he was awarded the 1935 Nobel Prize for Physics for the discovery). In 1932, Chadwick became Professor of Physics at the University of Liverpool where he built Britain's first cyclotron. It was here that much of the British research was carried out for the Manhattan atomic bomb project of the Second World War. Knighted for his war work Chadwick ended his career as Master of Gonville and Caius College, Cambridge.
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