- The new international system (SI) unit of radiation dose, expressed as absorbed energy per unit mass of tissue.
- The SI unit "gray" has replaced the older "rad" designation.
- 1 Gy = 1 Joule/kilogram = 100 rad.
- Gray can be used for any type of radiation (e.g., alpha, beta, neutron, gamma), but it does not describe the biological effects of different radiations.
- Biological effects of radiation are measured in units of "sievert" (or the older designation "rem").
- Sievert is calculated as follows: gray multiplied by the "radiation weighting factor" (also known as the "quality factor") associated with a specific type of radiation.