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Nuclear Glossary

The nuclear industry has an array of terms and units that are not too familiar to mainstream engineering. However, with nuclear energy making it's way back up the political agenda it may be about time we all learned some of the basics.

As always, if you have anything that can be added to the following glossary, then let us know.

Absorbed Dose

Energy from ionising radiation absorbed per unit mass of tissue.

Alpha Particle

Ionising radiation produced from the spontaneous decay of certain radioactive materials. An alpha particle consists of the nucleus of a Helium atom. Alpha particles are easily stopped by tissue or other material; therefore damage only occurs to tissue close to the radiation source.

Background Radiation

Ionising radiation present in the environment from cosmic rays and natural sources in the earth. Background radiation varies considerably with location.

Becquerel (Bq)

Unit of activity equal to one disintegration per second.

Beta Particles

Beta particles are subatomic particles ejected from the nucleus of some radioactive atoms. They are equivalent to electrons. The difference is that beta particles originate in the nucleus and electrons originate outside the nucleus. While beta particles are emitted by atoms that are radioactive, beta particles themselves are not radioactive. It is their energy, in the form of speed that causes harm to living cells. Beta particles travel several feet in open air and are easily stopped by solid materials.


Thin walled metal enclosure that forms the outer shell of nuclear fuel and prevents the release of plutonium dioxide and alpha particles into the environment.

Committed Effective Dose Equivalent

The sum of the committed dose equivalents to various tissues of the body, expressed in Sieverts (rem).

Curie (Ci)

A measure of the radioactivity level of a substance i.e. the number of unstable nuclei that are undergoing transformation in the process of radioactive decay. One curie equals the disintegration of 3.7 x 1010 (37 billion) nuclei per second and is equal to the radioactivity of one gram of Radium-226.

Decay Heat

The heat produced by the energy of decay of radionuclides.


The decrease in the amount of any radioactive material over time due to the transformation of one nuclide into a different nuclide or into a different energy state of the same nuclide. The decay process results in the emission of nuclear radiation (alpha, beta and gamma) and heat.


The reduction or removal of radioactive contaminants from surfaces of equipment by washing with chemicals, by wet abrasive blasting, or by chemical processing.


The amount of energy deposited in the body by ionising radiation per unit body mass.

Dose Commitment

The dose an organ or tissue would receive during a specified period of time as a result of intake, e.g. ingestion or inhalation, of one or more radionuclides from a defined release.

Half Life

The period required for the disintegration of half the atoms in a given amount of a specific radioactive substance. The half life varies for specific radioisotopes.

Ionising Radiation

Any radiation capable of displacing electrons from atoms or molecules, thereby producing ions.


One of perhaps several different species of a given chemical element with the same number of protons, which are distinguishable by variations in the number of neutrons in the atomic nucleus but indistinguishable by chemical means.

LSA Scale

Low Specific Activity scale found adhering to pipe and equipment internals. Mainly due to radium-226 produced from the decay of naturally occurring uranium-238.


A heavy artificially produced radioactive metal with 15 isotopes. It has an atomic number of 94.


The emitted particles (alpha, beta, neutrons) or photons (gama) from the nuclei of unstable (radioactive) atoms as a result of radioactive decay.


The spontaneous decay or disintegration of unstable atomic nuclei, usually accompanied by the emission of ionising radiation.


Unstable isotopes of an element that decay or disintegrate and spontaneously emit particles or electromagnetic radiation.


The unit dose representing the amount of ionising radiation needed to produce the same biological effects as one roentgen of high penetration X-rays (about 200kv).

Sievert (SV)

The SI unit of dose equivalent. One Sv is equivalent to 100 rem.

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