James Chadwick

James Chadwick was born in 1891 in Bollington, a small mill town in Cheshire, England, and was brought up mostly in his grandmother’s care; his parents ran a laundry. Scholarships carried him from the local grammar school to the University of Manchester, where a clerical mix-up enrolled him in physics rather than the mathematics he had applied for — and the shy teenager, meaning to correct the error eventually, found he liked the subject too much to leave. He stayed on for a master’s degree under Rutherford, then moved to Berlin in 1913 to work with Hans Geiger, one of the sharpest hands in the new radioactivity. War trapped him there: interned for four years in the Ruhleben camp, he and a fellow prisoner did what physics they could in a horse stable, with improvised apparatus and short rations.

Back in England he followed Rutherford to the Cavendish Laboratory in Cambridge in 1919 and became the quiet engine of the hunt Rutherford had proposed in 1920: if a proton and an electron could fuse, an atom should exist with no charge at all. In 1930 the Germans Bothe and Becker found that beryllium bombarded with alpha particles emitted a radiation of extraordinary penetrating power, and in 1932 the Joliot-Curies showed it could knock protons flying out of paraffin wax — but read it as a strange kind of gamma ray. Chadwick, knowing the energies refused to balance, worked without rest through February 1932 and sent Nature the answer: the radiation was not radiation at all but a stream of neutral particles, each about as heavy as a proton — the neutron Rutherford had imagined and named. The 1935 Nobel Prize in Physics followed.

The neutron explained isotopes in one stroke — atoms of one element, identical protons, differing neutrons — and, because it carries no charge and can walk unopposed into any nucleus, it became the master key of the nuclear age: within seven years came fission, and with it reactors and the neutron-made medical isotopes hospitals use every day. Chadwick spent that war inside the problem: on the MAUD committee that judged an atomic bomb feasible, then as head of the British Mission to the Manhattan Project at Los Alamos, where the famously quiet Englishman became General Groves’s trusted channel for British science. Knighted in 1945, he led Britain’s Atomic Energy Research Establishment at Harwell and finished his career as Master of Gonville and Caius College, Cambridge. He died in 1974, quiet to the last.