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 (unit) 1962 it was redefined. The CCU decided to define the SI unit of absorbed radiation in terms of energy per unit mass, which in MKS units was J/kg. This was confirmed in 1975 by the 15th CGPM, and the unit was named the "gray" in honour of Louis Harold Gray, who had died in 1965. The gray was equal to 100 rad. The definition of the roentgen had had the attraction of being relatively simple to define for photons in air, but the gray is independent of the primary ionizing radiation type, and can be used for both kerma and