John Cockcroft
1897–1967, Todmorden, Yorkshire, England, Cambridge, England
British physicist who, with Ernest Walton, achieved the first fully artificial transmutation of an atomic nucleus using artificially accelerated particles.
Cockcroft studied mathematics at Manchester and electrical engineering at the Manchester College of Technology before the First World War, during which he served in the Royal Field Artillery. In 1920 he went to Cambridge to study mathematics, and in 1924 he joined Rutherford's Cavendish Laboratory, where he began the high-voltage acceleration of protons that made him famous. During the Second World War he worked on radar and headed the Anglo-Canadian nuclear laboratory at Chalk River; in 1946 he became the founding director of the Atomic Energy Research Establishment at Harwell. He was knighted in 1948.
Nobel-winning work
Working at the Cavendish Laboratory, Cockcroft and Ernest Walton designed and built a voltage-multiplier accelerator — the 'Cockcroft–Walton' generator — that produced proton beams of several hundred kiloelectronvolts. In April 1932 they directed protons of roughly 400–700 keV at a lithium target and observed the emission of two alpha particles — the first fully artificial disintegration of an atomic nucleus by artificially accelerated particles.
The experiment showed that the lithium-7 nucleus, after capturing a proton, splits into two helium nuclei, and the measured energies agreed with Einstein's mass–energy relation E = mc². Announced in 1932, this 'splitting of the atom' founded accelerator-based nuclear physics; Cockcroft and Walton shared the 1951 Nobel Prize in Physics 'for their pioneer work on the transmutation of atomic nuclei by artificially accelerated atomic particles'.
Workplaces: Cavendish Laboratory, University of Cambridge, Atomic Energy Research Establishment, Harwell
United Kingdom