Radiation exposure is a measure of the ionization of air due to ionizing radiation from high-energy photons (i.e. X-rays and gamma rays). 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 given the symbol X. The SI unit of radiation exposure is the coulomb per kilogram (C/kg), but in practice, the roentgen is used.
Radiation Exposure Rate
The radiation exposure rate is the rate at which an exposure is received. It is a measure of exposure intensity (or strength). The exposure rate is therefore defined as:
In conventional units, it is measured in mR/sec or R/hr. Since the amount of radiation exposure depends directly (linearly) on the time people spend near the source of radiation, the exposure is equal to the strength of the radiation field (exposure rate) multiplied by the length of time spent in that field. It must be emphasized that this concept applies only to X-rays or γ-rays in air at a point outside a body. Radiation exposure is not applicable to describe neutrons, charged particles or all interactions taking place within a body.