Radiological Information & Glossary - Radiation Measurements
The amount of energy absorbed by matter received from ionizing radiation per unit mass of matter; expressed in rads.
A measure of the ionization produced in air by X- or gamma radiation, and expressed in roentgens (R). Although "dose" and "exposure" are often used interchangeably, the former (dose) is a measurement of energy absorbed in body tissue, and the latter (exposure) is a measurement of ionization in the air due to the presence of radiation.
Rad
Unit of radiation dose
Unit of exposure, applicable only to X- and gamma radiations.
Rem
A unit used to express all types of ionizing radiation on a common scale to indicate relative biological effects.

For beta and gamma radiation: exposure to 1 roentgen delivers a dose of 1 rad, which is equivalent to 1 rem.

Amount of radioactive material in which 37 billion atoms decay per second. The rate at which radioactive material is released to the environment may be expressed in units of curies per second (Ci/sec.).
One-thousandth of a unit (10-3), i.e., millirem (mRem) or milliroentgen (mR).
One-millionth of a unit (10-6).
One trillionth of a unit (10-12).

Dose limits are prescribed by the NRC per the Code of Federal Regulations, Title 10, Section 50. They include five (5) parameters identified from the second International Conference on Radiation Protection. These parameters are identified and defined below.

Biological effect to the entire human body, as a result of liquid effluents.
Biological effect to an organ most affected by the liquid effluent (Liver, Kidney, Thyroid, Lung, Bone, or the Gastro-Intestinal tract).
A measure of energy (radiation) in air from Beta-emitting noble gas isotopes
A measure of energy (radiation) in air from Gamma-emitting noble gas isotopes
Biological effect to the human body from airborne radioactive emissions of Iodine or particulate matter.