Cockcroft was born in Todmorden, England, on May 27, 1897, the son of a textile manufacturer. After completing secondary school at Todmorden in 1914, he entered Manchester University. He left the university after only one year to join the British army and enter World War I. He survived some of the worst battles of the war and returned to take a job at the Metropolitan Vickers Electrical Company. Officials at Vickers encouraged him to return to college and, in 1924, he earned his bachelors degree from St. John's College, Cambridge. After graduation, he joined Ernest Rutherford's (1871-1937) research team at the Cavendish Laboratory. While at the Cavendish, Cockcroft met the Russian physicist George Gamow (1904-1968) who outlined a new theory about particle bombardment. Gamow explained that his calculations showed that subatomic particles with a relatively modest amount of kinetic energy had a small, but significant, probability of entering atomic nuclei and causing their disintegration.To test this theory, Cockcroft, working with E. T. S. Walton, designed a machine to accelerate protons. The machine had the ability to generate voltages greater than 500,000 volts. Protons introduced at one end of the machine wereaccelerated by this potential difference and then directed at a lithium target at the opposite end of the machine. Cockcroft and Walton found that the product of the reaction between protons and lithium nuclei was alpha particles (helium nuclei):
1H1 + 3Li7 = 22He4
Evidently the protons had entered the lithium nucleus and then caused it to break apart into two alpha particles. This reaction was the first nuclear change brought about by artificially accelerated particles. Cockcroft and Waltonrepeated this experiment using other targets, such as boron, carbon, fluorine, and other elements. They found similar results with these elements. With boron as a target, for example, three alpha particles were produced:
1H1 + 5B11 = 32He4
Shortly after deuterium was discovered, the two researchers began using deuterons as projectiles in their accelerator. When World War II began, Cockcroftonce more put his talents to work for Great Britain. He was appointed Chief Superintendent of the Government's Air Defence Research and Establishment. Inthat position, he contributed to the development of the nation's radar defense system. He was also involved in the development of nuclear energy as head of the Canadian Atomic Energy Project. After the war, he became director of the first atomic energy research laboratory at Harwell, England. Cockcroft andWalton were awarded the Nobel Prize in Physics in 1951 for the development oftheir particle accelerator and for the transmutation of atomic nuclei. In 1961, Cockcroft also received the Atoms for Peace award. He died in Cambridge on September 18, 1967.