Exposure

Ionizing radiation produces ionization when it passes through any material. However, a special unit is used when referring to x-ray and gamma radiation when it produces ionization in air by liberating electrons from the air molecules by the process of ionization. The quantity of ionization in air is called exposure. The method used to determine the exposure resulting from an x-ray or gamma field is to measure the amount of charge produced (ionization) in a measured volume of air. The units used to identify exposure are the roentgen (R) or coulombs/kilogram (c/kg). The roentgen is defined only for gamma and/or x-ray radiation, with an energy of less than 3 MeV, in air and is the amount of gamma or x-ray radiation required to produce 1 statcoulomb of charge in 1 cubic centimeter of air at standard temperature and pressure (STP).

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