Roentgen equivalent man has been defined since 1976 as equal to 0.01 sievert, which is the more commonly used SI unit outside the United States. A number of earlier definitions going back to 1945 were derived from the roentgen unit, which was named after Wilhelm Röntgen, a German scientist who discovered X-rays. 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. Older units of rem following other definitions are up to 17% smaller than the modern rem. One rem carries with it a 0.05% chance of
Roentgen equivalent man sievert in 1980, but never accepted the use of the rem. The US National Institute of Standards and Technology (NIST) recognizes that this unit is outside the SI, but temporarily accepts its use in the US with the SI. The rem remains in widespread use as an industry standard in the US. The United States Nuclear Regulatory Commission still permits the use of the units curie, rad and rem alongside SI units. The following table shows radiation quantities in SI and non-SI units: Roentgen equivalent man The roentgen equivalent man (or rem) is an older, CGS unit of equivalent dose,