Joule of ionizing radiation by one kilogram of matter (J/kg)

The joule per kilogram (symbol: J/kg) is the fundamental SI coherent derived unit for absorbed dose, defined as one joule of radiation energy deposited into one kilogram of matter. Although dimensionally identical to units used for specific energy, the 15th CGPM assigned the distinct name gray to J/kg when measuring radiation absorbed dose in 1975, ensuring clear distinction from related dose equivalent quantities measured in sieverts.