In radiation protection, the sievert is a derived unit of equivalent dose and effective dose. The sievert represents the equivalent biological effect of the deposit of a joule of gamma rays energy in a kilogram of human tissue. Unit of sievert is of importance in radiation protection and was named after the Swedish scientist Rolf Sievert, who did a lot of the early work on dosimetry in radiation therapy.
The unit rem (an abbreviation for Roentgen Equivalent Man) is the non-SI unit of the equivalent dose, which is used predominantly in the USA. The rem represents the equivalent biological effect of the deposit of one hundred ergs (one rad) of gamma rays energy in a kilogram of human tissue. The rem is not derived from the unit of exposure, the roentgen. The acronym is now a misleading historical artifact, since 1 roentgen actually deposits about 0.96 rem in soft biological tissue, when all weighting factors equal unity.
Equivalent doses measured in industry and medicine often have usually lower doses than one rem, and the following multiples are often used:
1 mrem (millirem) = 1E-3 rem
1 krem (kilorem) = 1E3 rem
Conversions from the SI units to other units are as follows:
- 1 Sv = 100 rem
- 1 mSv = 100 mrem