gray (Gy):

  • 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.

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