Conversion: Exposure to Absorbed Doseĭose is defined as the amount of energy deposited by ionizing radiation in a substance. For example, if soft tissue is exposed to γ-rays of 1 R, the radiation dose will be approximately 9.3 milligray (mGy). To calculate the radiation dose (in Gy) from a radiation exposure of 1 R depends on the energy of the X-rays or γ-rays and the composition of the irradiated material. Radiation exposures measured in industry (except nuclear medicine) often have comparable doses to one roentgen and the following multiples are often used: As a result, one roentgen corresponds to 2.58 x 10 -4 coulomb per kg of ions generated in air and an exposure of one coulomb per kilogram is equivalent to 3876 roentgens. In the original definition 1 R means the amount of X-rays or γ-radiation that is required to liberate positive and negative charges of one electrostatic unit of charge (esu) in 1 cm³ of dry air at standard temperature and pressure (STP). The roentgen, abbreviated R, is the unit of radiation exposure. The SI unit of radiation exposure is the coulomb per kilogram (C/kg), but in practice, the roentgen is used. Radiation exposure is given the symbol X. Radiation exposure is defined as the sum of electrical charges (∆q) on all the ions of one sign produced in air when all the electrons, liberated by photons in a volume of air whose mass is ∆m, are completely stopped in air. Radiation exposure is a measure of the ionization of air due to ionizing radiation from high-energy photons (i.e.