The Gray [ ɡreɪ̯ ] ( unit symbol Gy ) is a derived SI units joules and kilograms size. It indicates the absorbed dose caused by ionizing radiation and describes the energy absorbed per unit mass. The Kerma is measured in Gray.
The unit is the ratio of the absorbed energy and the mass of the body. 1 Gy = 1 J / kg = 100 rd.
It is used primarily for use in medicine, for instance for indication of the applied radiation dose in radiation therapy, or nuclear medicine therapy.
Relation to other units
In order to better compare the different types of radiation absorbed dose in terms of harmful effects for organisms, it is multiplied by a weighting factor, the radiation weighting factor. Through him, the relative biological effectiveness of the radiation is taken into account. Since the radiation weighting factor is a dimensionless number, the equivalent dose and the absorbed dose have the same dimension. However, to emphasize the difference between the dose quantities for practical use and because the numerical value of the dose size can change by the radiation weighting factor also be used for energy doses Gray, for weighted dose quantities Sievert.
Wheel ( traditional unit )
Until 31 December 1985, the official unit of absorbed dose was the rad ( unit symbol rd).