Roentgen (unit) absorbed dose in a wide range of matter. When measuring absorbed dose in a human due to external exposure, the SI unit the gray, or the related non-SI rad are used. From these can be developed the dose equivalents to consider biological effects from differing radiation types and target materials. These are equivalent dose, and effective dose for which the SI unit sievert or the non-SI rem are used. The following table shows radiation quantities in SI and non-SI units: Roentgen (unit) The roentgen or röntgen () (symbol R) is a legacy unit of measurement for the exposure of X-rays
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,