Radiation Doses

Dose is the quantity of ionizing radiation absorbed, per unit of mass, by the body or by any portion of the body. There are two types of radiation doses:

• Absorbed dose is the amount of radiation absorbed by an object or person. The unit of measure for absorbed dose is the rad (U.S. unit) or the gray (Gy, international unit). An absorbed dose of 1 rad means that 1 gram of material absorbed 100 ergs of energy from ionizing radiation.
• Effective dose is the amount of radiation absorbed by a person, adjusted to account for the type of radiation received and the effect on a person's organs. The unit of measure for effective dose is rem (U.S. unit) or sievert (Sv, international unit). The dose equivalent is the same as the absorbed dose for beta and gamma radiation. For alpha and neutron radiation, however, the dose equivalent is larger than the absorbed dose, because they are more damaging to the human body.

Note that more commonly, dose is measured in smaller units called millirems. A millirem (mrem) is one thousandth of a rem.

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