Photo from the Nobel Foundation archive.
Sir John Douglas Cockcroft
Born: 27 May 1897, Todmorden, United Kingdom
Died: 18 September 1967, Cambridge, United Kingdom
Affiliation at the time of the award: Atomic Energy Research Establishment, Harwell, Berkshire, United Kingdom
Prize motivation: "for their pioneer work on the transmutation of atomic nuclei by artificially accelerated atomic particles."
Prize share: 1/2
John Cockcroft was born into an English family active in the cotton industry. He studied mathematics and electrotechnical engineering in Manchester, with a break for military service during World War I. After working for a couple of years in electrotechnology, he came to Cambridge in 1924. Among other things, he started the Cavendish Laboratory there. During World War II he worked on developing radar. After the war he worked primarily within the UK Atomic Energy Authority. John Cockcroft married in 1925 and had four daughters and a son.
Ernest Rutherford used alpha particles from radioactive elements to study nuclear reactions and used his findings to convert nitrogen into oxygen. However, only a very few nuclear reactions could be achieved using alpha particles. John Cockcroft and Ernest Walton developed a device, an accelerator, to generate more penetrating radiation. Using a strong electric field, protons were accelerated to high velocities. In 1932, they bombarded lithium with protons, causing their nuclei to split and producing two alpha particles.