Note 2 — Radioisotopes as Radiation Sources

The roentgen is a measure of ionizing radiation, as the foot-candle is a measure of light. In simple terms the roentgen is that amount of X or gamma radiation which produces one electrostatic unit (esu) of electricity in one cubic centimeter (cc) of dry air at standard conditions of temperature and pressure. This may sound like a trivial amount of energy, but it amounts to more than two billion ionizations in each cubic centimeter.