Louis Harold Gray

Louis Harold Gray FRS (10 November 1905 – 9 July 1965) was an English physicist who worked mainly on the effects of radiation on biological systems. He was one of the earliest contributors of the field of radiobiology. Amongst many other achievements, he defined a unit of radiation dosage (absorbed dose) which was later named after him as an SI unit, the gray.

Early life Gray was born as an only child on 10 November 1905 to parents Harry and Amy Gray. His father worked at a post office.

Career 1933 – Hospital physicist at Mount Vernon Hospital, London 1936 – Developed the Bragg–Gray equation, the basis for the cavity ionization method of measuring gamma-ray energy absorption by materials 1937 – Built an early neutron generator at Mount Vernon Hospital 1938 – Studied biological effects of neutrons using the generator 1940 – Developed concept of RBE (Relative Biological Effectiveness) of doses of neutrons 1952 – Initiated research into cells in hypoxic tumors and hyperbaric oxygen 1953 – Oliver Scott established the British Empire Cancer Campaign Research Unit in Radiobiology at Mount Vernon Hospital with Hal Gray as director which in 1970 became the Cancer Research Campaign's Gray Laboratory and then (in 2001) the Gray Cancer Institute. 1953–1960 – Under Gray's direction, Jack W. Boag developed pulse radiolysis 1962 – Ed Hart, of Argonne National Laboratory, and Jack Boag discovered the hydrated electron using pulse radiolysis at the Gray Laboratory – this discovery initiated a new direction of research that is still very active today and is vital for understanding the effects of radiation on biological tissue, for instance in cancer treatment.