Former measuring variable used in dosimetry for ionizing radiation. The unit of the ion dose is coulomb divided by kilogram (C/kg). 1 coulomb divided by kilogram is equal to the ion dose generated during the generation of ions of a preceding sign with an electric charge of 1 C in air with a mass of 1 kg caused by ionizing radiation of energy flux density constant in space. By the end of 1985 the unit roentgen (symbol: R) was accepted. 1 roentgen is equal to 258 µC/kg.