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 Roentgen equivalent man The roentgen equivalent man (or rem) is an older, CGS unit of equivalent dose, effective dose, and committed dose which are measures of the health effect of low levels of ionizing radiation on the human body. Quantities measured in rem are designed to represent the stochastic biological risk of ionizing radiation; primarily radiation-induced cancer. These quantities are derived from absorbed dose, which in the CGS system has the unit rad which is also an older unit. There is no universally applicable conversion constant from rad to rem; the conversion depends on relative biological effectiveness (RBE). The rem