John Douglas Cockcroft (1897-1967) was an English physicist. His main contribution to physics consisted in designing a linear accelerator capable of giving such a speed to charged particles as to produce the transmutation of atomic nuclei.
John Cockcroft was born in Todmorden, Lancashire, on May 27, 1897. He attended the University of Manchester, where he studied mathematics under Horace Lamb in 1914-1915. Following service with the Royal Field Artillery in World War I, Cockcroft joined Metropolitan-Vickers, an engineering company, which sent him back to the University of Manchester to study electrical engineering. He transferred to St. John's College, Cambridge, where he took honors in mathematics in 1924.
Cockcroft was one of the gifted young physicists whom Ernest Rutherford gathered at the Cavendish Laboratory. By 1928 Cockcroft was at work on the problem of accelerating protons by high voltages, a task in which he was greatly helped by E.T.S. Walton. At the meeting of the Royal Society on April 28, 1932, it was announced that Cockcroft and Walton "had successfully disintegrated the nuclei of lithium and other light elements by protons entirely artificially generated by high energy potentials." Cockcroft and Walton shared the Nobel Prize in physics for 1951.
Cockcroft's rise in the British scientific establishment was spectacular. In 1934 he became the head of the Royal Society's Mond Laboratory in Cambridge. In 1939 he obtained the coveted Jacksonian chair in experimental physics and that year took charge of the practical implementation of the principle of radar for Britain's coastal and air defense. Following his return in 1940 from the United States as a member of the Tizard Mission, he became head of the Air Defense Research and Development Establishment. By 1944 he was in Canada directing the Canadian Atomic Energy Project, and upon returning to England in 1946 he was appointed director of the Atomic Energy Research Establishment at Harwell. His 12 years there saw the production of the British atomic bomb and also an impressive advance in the peaceful use of atomic energy, exemplified by the construction of the famous nuclear energy power station at Calder Hall.
From 1959 until his death on Sept. 18, 1967, he was master of Churchill College while retaining a part-time membership in the British Atomic Energy Authority. At the last meeting which Cockcroft attended in July 1967, he made interesting predictions about the future of technology and offered the following advice to youth: "Never finish your education. I did not know much about physics when I started to do research. Go on with your reading and going to meetings and continue to work in your spare time on your own subject. It is the only way." Perhaps the finest personal characteristic of Cockcroft was his disarming kindness. It earned him countless friends both within and outside his professional field. The same quality made him also a much admired family man. He married Eunice Elizabeth Crabtree in 1925, and they had four daughters and a son.
Biographical material on Cockcroft is in the Nobel Foundation's publication Nobel Lectures, Physics, 1942-1962: Including Presentation Speeches and Laureates' Biographies (1964). The voltage multiplier of Cockcroft and Walton is explained in Irving Kaplan, Nuclear Physics (1955; 2d ed. 1963). Volume 2 of Henry A. Boorse and Lloyd Motz, eds., The World of the Atom (2 vols., 1966), contains a chapter on Cockcroft and describes the Cockcroft-Walton experiments.