- The SI unit of absorbed dose of ionizing radiation, equivalent to 1 J/kg of tissue; 1 Gy = 100 rad. SYN: griseus. [Louis H. G., British radiologist, 1905–1965]
* * *gray or chiefly Brit grey 'grā n any of a series of neutral colors ranging between black and whitegray 'grā n the mks unit of absorbed dose of ionizing radiation equal to an energy of one joule per kilogram of irradiated material abbr. GyGray 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.
* * *n.the SI units of absorbed dose of ionizing radiation, being the absorbed dose when the energy per unit mass imparted to matter by ionizing radiation is 1 joule per kilogram. It has replaced the rad. Symbol: Gy.
* * *(gra) 1. of a hue between white and black. 2. a unit of absorbed radiation dose equal to 100 rads. Abbreviated Gy.
Medical dictionary. 2011.