Roentgen (unit) this derivative quantity the roentgen equivalent physical (rep) to distinguish it from the ICR roentgen. The introduction of the roentgen measurement unit, which relied upon measuring the ionisation of air, replaced earlier less accurate practices that relied on timed exposure, film exposure, or fluorescence. This led the way to setting exposure limits,and the National Council on Radiation Protection and Measurements of the United States established the first formal dose limit in 1931 as 0.1 roentgen per day. The International X-ray and Radium Protection Committee, now known as the International Commission on Radiological Protection (ICRP) soon followed with a limit of
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