or chiefly Brit  grey  n :  any of a series of neutral colors ranging between black and white gray or chiefly Brit  grey  adj 
, n :  the mks unit of absorbed dose of ionizing radiation equal to an energy of one joule per kilogram of irradiated material - abbr. Gy
 
Gray, Louis Harold (1905-1965), British radiobiologist. In 1933 Gray established a physics laboratory to measure radiation in the treatment of cancer at Mount Vernon Hospital, Middlesex, England. Earlier he and Sir W. H. Bragg had formulated a theory for deducing the energy absorbed by a material exposed to gamma rays from the ionization within a small gas-filled cavity in the material. At Mount Vernon he was to apply his theory to X rays and later, in modified form, to neutrons. Gray expressed the neutron dose values in energy units, anticipating the International Commission on Radiological Units, which in 1953 adopted the rad as the unit for measuring all types of ionizing radiation. In 1975 the Commission adopted the gray as the physical unit of dose.
 
 
 
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