Glossary of terms

The following table defines the terms associated with radioactive waste.

Term Definition
alpha emitter A radioisotope that emits an alpha particle when it decays.
alpha particle A positively charged particle containing two protons and two neutrons which is emitted by certain radioisotopes.
atom The smallest quantity of an element that can take part in a chemical reaction. Atoms are made up of a nucleus containing protons and neutrons, which is surrounded by clouds of electrons.
background radiation Low level radiation from small amounts of radioisotopes in the surrounding soil, water, atmosphere, buildings, and so forth.
becquerel (Bq) The international standard unit of measurement of radioactivity, defined as one radioactive disintegration per second.
beta emitter A radioisotope that emits a beta particle when it decays.
beta particle An electron or positron emitted by the nucleus of a radionuclide during radioactive decay.
cosmic radiation Radiation that reaches the Earth from outer space.
decay product The product of the spontaneous radioactive decay of a nuclide.
disposal The emplacement of waste in an approved, specified facility without the intention of retrieval.
engineered barrier A feature made or altered by humans that delays or prevents radionuclide migration from the waste or the disposal structure into its surroundings. It may be part of the waste package or part of the disposal structure.
gamma emitter A radioisotope that emits gamma rays when it decays.
gamma rays High energy radiation similar to X-rays.
irradiation Subjection to ionising radiation.
isotope One of two or more forms of a chemical element having the same number of protons but a different number of neutrons. All isotopes of the same element have the same chemical properties, and therefore cannot be separated by chemical means.
kilowatt (kW) One thousand watts. A watt is the international standard unit of measurement of power, equal to one joule per second.
near-surface disposal Disposal of waste, with or without engineered barriers, on or below the ground surface, where the final protective covering is of the order of a few metres thick, or in caverns a few tens of metres below the Earth's surface.
nuclide An atom of a particular element distinguished by the number of protons and neutrons in its nucleus.
radioactive waste Material that contains or is contaminated with radionuclides at concentrations or activities greater than clearance levels as established by the regulatory body, and for which no use is foreseen.
radiation Release of energy through the decay of unstable atoms.
radiography Production of images through use of radioactive materials, used in medicine, industry, etc.
radioisotope Any isotope which is unstable and undergoes natural radioactive decay.
radionuclide Any nuclide which is unstable and undergoes natural radioactive decay.
radiopharmaceutical A therapeutic drug that contains radioactive material.
sievert (Sv) The international standard unit of measurement of effective dose, dose being the amount of energy delivered to a mass of material by ionising radiation passing through it. The average person receives a dose of approximately 1.5 milliSieverts of background radiation each year. For more information on radiation doses, see Related documents.
storage Storage of radioactive materials such that isolation, monitoring, environmental protection and human control are provided, and subsequent action involving treatment, transport and disposal is expected.

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