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Glossary of Radiation Terms

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The following are a few basic radiation terms that are frequently used in the radiation protection community. This glossary is a subset of radiation terms listed on the EPA Radiation Protection Division's home page. For a more complete listing of radiation terms, follow this link: www.epa.gov/radiation/glossary/

alpha particle:A positively charged particle made up of two neutrons and two protons emitted by certain radioactive nuclei. Alpha particles can be stopped by thin layers of light materials, such as a sheet of paper, and pose no direct or external radiation threat; however, they can pose a serious threat if ingested.


ambient air:The atmosphere around a facility.


beta particle: An electron or positron emitted by certain radioactive nuclei. Beta particles can be stopped by aluminum. They pose a serious direct or external radiation threat and can be lethal, depending on the amount received.


curie: A measure of radioactivity. One curie of radioactive material will have 37 billion transformations of atoms (disintegrations) in one second.


dose:A general term denoting the quantity of radiation or energy absorbed. Dose may refer to absorbed dose, the amount of energy deposited per unit mass, or to equivalent dose, the absorbed dose adjusted for the relative biological effect of the type of radiation being measured.


dose equivalent:A unit of biologically equivalent dose, defined as the absorbed dose in rad multiplied by the quality factor (Q).


exposure: A term relating to the amount of ionizing radiation that is incident upon living or inanimate material.


gamma rays:High-energy electromagnetic radiation emitted by certain radioactive nuclei. These rays have high energy and a short wave length. Stopping gamma rays requires thick layers of dense materials such as lead. Gamma rays are potentially lethal to humans depending on the dose.


isotope:A nuclide having the same number of protons but a different number of neutrons.


mrem:One thousandth of a rem.


neutron:A small particle possessing no electrical charge typically found within an atom's nucleus.


nucleus:The central part of an atom that contains protons and neutrons.


nuclide:A general term applicable to all atomic forms of an element. Nuclides are characterized by the number of protons and neutrons in the nucleus.


picocurie: One one-trillionth (1/1,000,000,000,000 of a curie).


proton:A small particle, typically found within an atom's nucleus, that possesses a positive electrical charge.


quality factor (Q):Dependent factor by which absorbed doses are to be multiplied to account for the varying effectiveness of different radiations.


rad: An acronym for Radiation Absorbed Dose. The rad is a basic unit of absorbed radiation dose.


radioactive decay:The process in which a radioactive nucleus emits (gives off) radiation and changes to a different isotope or element. A number of different particles can be emitted by decay. The most typical are alpha, beta particles, and gamma rays.


radionuclide: A radioactive species of an atom having a characteristic nucleus.


rem: Roentgen Equivalent Man. A unit of absorbed dose.

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