The SI unit for the dose equivalent of ionizing radiation. One sievert represents a dosage of 1 → joule per kg of tissue, absorbed from the ionizing radiation. The effect of radiation depends on its total amount of energy, the type of radiation, and the energy levels of particular particles. The dose equivalent in sieverts of radiation is the product of the absorbed dose in → gray (Gy)s and a dimensionless numeric factor, called the quality factor or relative biological effectiveness, dependent on the type of radiation. The sievert has replaced the → rem as the unit of dose equivalent. 1 rem = 10-2 Sv.
The unit honors the Swedish physicist Rolf Sievert (1898-1966), who worked over many years to measure and standardize the radiation doses used in cancer treatment.