Louis Harold Gray (1905-1965), British physicist. After developing an boyhood interest in nuclear physics, Gray earned a scholarship to Trinity College, Cambridge, UK. He finished top of his year in the Natural Sciences Tripos and went on to work under Rutherford at the Cavendish Laboratory, Cambridge. His work in the effects of different radiation types led to the standard international (SI) unit for absorbed radiation being named the Gray (Gy), where 1 Gray is 1 joule absorbed per kilogram of matter. After the Second World War he was prominent in the development of radiation as a medical tool, particularly in the treatment of cancer.