Gray

The gray (Gy) is the international unit of measurement for the absorbed dose. This describes the amount of energy transferred to a certain mass of material by ionising radiation. One gray corresponds to one joule per kilogram. Joule is the physical unit of energy.

This unit is mainly used in radiology, radiotherapy and radiation protection to indicate the amount of energy absorbed by a particular material as a result of exposure to ionising radiation.

The unit of absorbed dose was named after the British physicist Louis Harold Gray.