John Cockcroft

John Cockcroft (1897-1967), English nuclear physicist, who shared the 1951 Nobel Prize for physics for designing the first particle accelerator (an instrument used to increase the energy of subatomic particles) and inducing the first artificial nuclear transformation of an element.

Born in Todmorden, Yorkshire, John Douglas Cockcroft was educated at the Manchester College of Technology and the University of Cambridge, where he studied mathematics and electrical engineering. After graduating from Cambridge in 1924, he worked at the Cavendish Laboratory under English physicist Ernest Rutherford and collaborated with Russian physicist Peter Kapitza to design and develop powerful electromagnets. Cockcroft’s interests soon turned to nuclear physics and the challenge of accelerating atomic particles in an electric field. During the 1920s the only particles used for bombarding and breaking down the atomic nucleus (a process known as atom smashing) were alpha particles emitted by naturally radioactive elements. Rutherford had thoroughly exploited this approach, and Cockcroft believed it necessary to find particles of still higher energies to improve the process.

In 1929 Cockcroft and colleague Ernest T. S. Walton developed a type of particle accelerator they called a voltage multiplier. It was a machine that could build up voltages and accelerate protons to energies higher than those of natural alpha particles. In 1932 Cockcroft and Walton bombarded lithium with these protons and produced alpha particles. In this reaction they managed to combine lithium and hydrogen to form helium; it was the first nuclear reaction induced by artificially accelerated particles.

In 1939 Cockcroft became a professor at the University of Cambridge. During World War II (1939-1945) he was appointed director of Britain’s air defense research and contributed to the development of that nation’s radardefense system. He was also involved in the development of nuclear energy and was director of the Canadian National Research Council. From 1946 to 1958 he served as the first director of the British Atomic Energy Research Establishment in Harwell, England. He was knighted for his accomplishments in 1948, and in 1951 he and Walton shared the Nobel Prize for physics. Cockcroft was appointed master of Churchill College in Cambridge in 1960 and received the Atoms for Peace award in 1961.