The
rad is a deprecated unit of
absorbed radiation dose, defined as 1 rad = 0.01
Gy = 0.01 J/kg. It was originally defined in
CGS units in 1953 as the dose causing 100
ergs of energy to be absorbed by one
gram of matter. It has been replaced by the
gray in
SI but is still used in some countries. A related unit, the
roentgen, is used to quantify the
radiation exposure. The
F-factor can be used to convert between rads and roentgens.