The rontgen or roentgen (R) is a unit of measurement of ionizing radiation in air, either X or gamma rays. It is named after the German physicist Wilhelm Rontgen. A roentgen is the amount of radiation required to liberate a pair of positive and negative charges from atoms of one electrostatic unit of charge in 1.00 cm3 of air at standard temperature and pressure. This corresponds to the generation of approximately 2.08 × 109 ion pairs. A dose of 500 R in five hours is lethal for humans.
If X radiation ionizes 18.6 × 1012 atoms per cemtimeter cubed, what is the ionizing intensity of the radiation measured in roentgens ?