A unit of exposure to gamma (or X) radiation.An exposure of 1 roentgen results in the deposition of about 94 ergs of energy in 1 gram of soft body tissue. Hence, an exposure of 1 roentgen is approximately equivalent to an absorbed dose of 1 rad in soft tissue. (Glasstone, The Effects of Nuclear Weapons, 3rd Ed., 1977, Glossary, p. 638)