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Cockcroft, Sir John Douglas

research particles nuclear transmutation

(1897–1967) British physicist: pioneered the transmutation of atomic nuclei by accelerated particles.

Cockcroft had completed only his first year at Manchester University when the First World War broke out and he joined the Royal Field Artillery as a signaller. Remarkably he survived unscathed through 3 years and most of the later battles. Afterwards, he studied electrical engineering at Manchester and then joined the Metropolitan Vickers Electrical Company and took his degree at Cambridge in mathematics (1924). He then became part of research team at the Cavendish and in 1932 made his reputation by a brilliant experiment with E T S Walton (1903–95), for which they received the 1951 Nobel Prize for physics.

Cockcroft was methodical in his work, genial and decisive, and no waster of words. He soon became mainly interested in research management, and in 1940 was a member of the Tizard Mission to the USA to negotiate wartime technological exchange. He then became head of the Air Defence Research and Development Establishment (1941–4). He was also Jacksonian Professor at Cambridge (1939–46). He became founding director of the Atomic Energy Research Establishment at Harwell (1946) and led the establishment of the Rutherford High-Energy Laboratory at Harwell (1959). In 1959 he became founding Master of Churchill College, Cambridge. Receiving many honours, Cockcroft became a leading statesman of science, combining research and administrative skills.

The experiment conducted by Cockcroft and Walton was triggered by mentioning (1928) to Cockcroft that bombarding particles may enter a nucleus by quantum mechanical ‘tunnelling’. This could occur at much lower incident energies than those required to overcome repulsion between the two. Using skilfully built voltage-doublers, protons were accelerated to 0.8 MeV and directed at a lithium target. Alpha particles (helium nuclei) were found to be released; the first artificially induced nuclear reaction (transmutation) was occurring; and was later shown to be:

(In his experiments on transmutation, Rutherford had used, as projectiles, particles from a natural radioactive source.) With the publication of this exciting result the nuclear era began, and cyclotrons and linear accelerators were built to study nuclear physics.

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