The SI unit of the absorbed dose of ionizing radiation, corresponding to one joule per kilogram.
- The sievert is numerically equivalent to the gray for electrons and for X-rays irradiating the whole body.
- Radiation doses are measured in rads or grays, where 1 gray equals 100 rads.
- Thus for these particular radiations the dose equivalent in sieverts is numerically equal to the absorbed dose in grays.
1970s: named after Louis H. Gray (1905–65), English radiobiologist.