roentgen (R) /rent″gən, ren″jən/ [Wilhelm K. Roentgen, German physicist, 1845–1923] , the quantity of x-radiation or gamma radiation that creates 1 electrostatic unit of ions in 1 mL of air at 0° and 760 mm of pressure. In radiotherapy or radiodiagnosis, the roentgen is the unit of the emitted dose. See also radiation absorbed dose, rem.
