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 as the unit of equivalent dose in 1962 to measure the way different types of radiation distribute energy in tissue, and began recommending values of relative biological effectiveness (RBE) for various types of radiation. In practice, the unit of rem was used to denote that an RBE factor had been applied to a number which was originally in units of rad or roentgen. In 1977 the rem was redefined by the ICRP as 0.01 sievert or 0.01 J/kg, with the intention that the sievert would come to replace the rem. The International Committee for Weights and Measures (CIPM) adopted the