Radiation may be any type of subatomic particle that is emitted by a body, including light, radio waves and X-rays. In common use, however, the term "radiation" frequently refers specifically to ionizing radiation. This type of radiation is sufficiently energetic to cause electrons to detach from their atoms, thus ionizing them. Some measures of radiation are objective and based on the number of particles that a body emits in a certain period time. Other measures of radiation attempt to measure their effect on organisms.
Use the roentgen (R) to measure ionizing radiation. This measure is defined as the radiation needed to free the ion pairs in one electrostatic unit of charge (esu) in one cubic centimeter of dry air under standard conditions.
Measure the biological effects of radiation on humans. The roentgen equivalent in man (rem) is the product of the absorbed radiation in roentgens and a radiation weighting factor. This weighting factor is an estimate of the effect that the radiation in question has on the human body. If the weighting factor is 1, then 1 rem is equal to 1.07185 roentgens.
Define the radiation absorbed dose (rad). This objective measure of radiation is defined as that dose of radiation that will cause 0.01 joule of energy to be absorbed by a kilogram of mass.
Use the gray as the standard unit of measure for absorbed radiation. A gray of radiation is the absorption of one joule of energy by a kilogram of mass. One gray is therefore equal to 100 rads.
Measure the equivalent dose of radiation in sieverts. This measure assesses the effect of radiation on living tissue by multiplying the absorbed radiation in grays by a quality factor. A sievert is therefore equal to a gray when the quality factor is 1.