A measure of the ability of x-rays or radioactive decay products to produce ionization in air. One roentgen corresponds to the absorption of about 86 ergs (100 ergs = 6.24 x 10 million electron volts, MeV) of energy from x- or gamma radiation, per gram of air. The corresponding absorption of energy in tissue may be from one-half to two times as great, depending on the energy and type of the radiation and the chemical composition of the tissue.
