roentgen
unit of radiation
unit of X-radiation (X-ray) or gamma radiation (gamma ray), the amount that will produce, under normal conditions of pressure, temperature, and humidity, in 1 kg (2.2 lbs) of air, an amount of positive or negative ionization equal to 2.58×10−4 coulomb. It is named for the German physicist Wilhelm Conrad Röntgen (Röntgen, Wilhelm Conrad). See also rem.