Absorbed dose is the quantity of ionizing radiation received per unit mass within a given period of time. The SI unit of absorbed dose is the gray (Gy). One gray is the absorbed dose when the energy per unit mass imparted to matter is 1 joule per kilogram. A former unit, the rad, = 0.01 gray.
Different materials that receive the same exposure may not absorb the same amount of energy. The absorbed dose (D) due to an amount of energy (E) being absorbed by a unit mass (m) of absorbing material is D = E/m.
The absorbed dose rate is the absorbed dose per unit of time. Its unit is the Gy/h.
See also equivalent dose.