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Glossary A - C


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Agreement State

A state that has signed an agreement with the Nuclear Regulatory Commission allowing the state to regulate the use of by-product radioactive material within the state.

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 health threat if ingested or inhaled.

Ambient Air

The air that surrounds us


A silvery metal; it is a man-made element whose isotopes americium-237 through -246 are all radioactive. Americium-241 is formed spontaneously by the beta decay of plutonium-241. Trace quantities of americium are widely used in smoke detectors.


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Beta Particle

An electron or positron emitted by certain radioactive nuclei. Beta  particles can be stopped by aluminum.  They can pose a serious direct or external radiation threat and can be lethal depending on the amount received.  They also pose a serious internal radiation threat if inhaled or ingested.


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A metal that may be stable (non radioactive) or unstable (radioactive). The most common radioactive form of cesium is cesium-137. Another fairly common radioisotope is cesium-134. Cesium-137 is much more significant as an environmental contaminant than cesium-134. It is also very useful in industry for its strong radioactivity.


The deposition of unwanted radioactive material on the surfaces of structures, areas, objects, or people. It may also be airborne, external, or internal (inside components or people).


A measure of radioactivity based on the observed decay rate of approximately one gram of radium.  The Curie was named in honor of Pierre and Marie Curie exit EPA, pioneers in the study of radiation. One curie of radioactive material will have 37 billion atomic transformations (disintegrations) in one second.

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