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GLOSSARY
Alpha particles: positively charged particles emitted from some radionuclides during radioactive decay. An alpha particle contains the same components as a nucleus of a helium atom (two protons and two neutrons). They travel very short distances in air. Alpha-emitting radionuclides are of most concern to humans if ingested or inhaled.
Atom: the smallest part of an element that still has all properties of that element. Its nucleus consists of protons and neutrons and is surrounded by orbiting electrons.
Background radiation: the amount of radiation to which a member of the population is exposed from natural sources, such as naturally occurring radionuclides in the soil, cosmic radiation occurring in outer space, and naturally occurring radionuclides deposited in the human body.
Beta particles: negatively charged particles emitted from the nucleus of an atom and having a mass and charge equal to that of an electron. Fast moving, energetic, beta particles can penetrate the skin. Beta emitting radionuclides are both an internal and an external hazard.
Curie (Ci): a quantity of radioactive material in which 3.7 x 1010 atoms are disintegrating per second (3.7 x 1010 Bq).
Class A waste: includes radionuclides with the lowest concentrations and short half-lives and constitutes 95% of all low-level waste.
Class B waste: allows intermediate concentrations of both long-lived and short-lived radionuclide materials. Class B wastes must also meet certain stability requirements.
Class C waste: allows the highest concentrations of both long-lived and short-lived radionuclide materials. Class C wastes must be disposed of in conformance with intrusion-barrier and depth requirements.
Compact: a group of two or more states formed to manage low-level radioactive waste on a regional basis. Forty-two states have formed nine compacts.
Decommissioning: the process of closing down a facility followed by reducing residual radioactivity to a level that permits the release of the property for unrestricted use criteria (10 CFR 20.1003).
Element: an atom with a unique number of protons in its nucleus. For example, oxygen has eight protons in its nucleus, and plutonium has 94.
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Gamma ray: a penetrating, short-wavelength electromagnetic radiation emitted during the radioactive decay of many radioactive materials. Except for their origin (the nucleus of the atom, rather than the outer electron shells) and higher energy, their characteristics are similar to those of x-rays. Gamma radiation is the most penetrating of the common kinds of ionizing radiation and is of concern as an external and internal radiation hazard.
Half-life: the time in which half a collection of atoms of a particular radioactive substance disintegrate into atoms of another element. Half-lives range from millionths of a second to billions of years.
High-level radioactive waste (HLW): (1) Irradiated (spent) reactor fuel. (2) Liquid waste resulting from the operation of the first-cycle solvent-extraction system, and the concentrated wastes from later extraction cycles, in a facility for reprocessing irradiated reactor fuel. (3) Solids into which such liquid wastes have been converted. HLW is primarily in the form of spent fuel discharged from commercial nuclear power reactors. It also includes some reprocessed material from defense activities and a small quantity of reprocessed commercial HLW (10 CFR Part 60) (USNRC, 1999b).
Isotopes: nuclides that have the same number of protons in their nuclei, and hence the same atomic number, but that differ in the numbers of neutrons, and therefore in the mass number; chemical properties of isotopes of a particular element are almost identical.
Low-level waste (LLW): includes wastes that are not high-level wastes (HLW), transuranic waste (TRU), naturally occurring radioactive materials (NORM), or source-material waste defined under the Atomic Energy Act Section 11.(e) (2). LLRW includes waste that come principally from nuclear power generation; hospitals and medical, educational, and research institutions; industries; private or government laboratories; and other nuclear fuel-cycle facilities (such as, fuel fabrication plants).
Mixed low-level radioactive and hazardous waste (mixed LLW): is defined as waste that satisfies the definition of low-level radioactive waste (LLRW) in the Low-Level Radioactive Waste Policy Amendments Act of 1985 (LLRWPAA) and contains hazardous waste that either (1) is listed as a hazardous waste in Subpart D of 40 CFR Part 261 or (2) causes the LLRW to exhibit any of the hazardous-waste characteristics identified in Subpart C of 40 CFR Part 261.
Positron emission tomography (PET): a non-invasive, diagnostic imaging technique for measuring the metabolic activity of cells in the human body. It is useful clinically in patients with conditions affecting the brain and the heart and in patients with particular types of cancer.
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Radioactivity: a property of radioactive material whereby atoms undergo spontaneous transformation at a predictable and measurable rate. Units of activity are the becquerel (Bq) and curie (Ci); 1 Ci = 3.7 x 1010 disintegrations per second, and 1 Bq = 1 disintegration per second.
Radioimmunoassay: quantitative determination of antigen and antibody concentrations by the introduction of a radioactively labeled, complimentary substance that can be expected to bind to the molecules in question and the measurement of a resulting radioactive immune complex.
Radioactive contamination: radioactive material that is present in an unwanted location and has no useful purpose.
Radionuclide: a radioactive species of an atom characterized by the constitution of its nucleus.
Sealed source: any special nuclear material or byproduct encased in a capsule designed to prevent leakage or escape.
Waste, radioactive: solid, liquid, and gaseous materials derived from licensed radioactive material operations that contain radioactive material in licensed amounts for which there is no further useful purpose. Wastes are classified as high-level waste (HLW) as defined in 10 CFR 60 or as low-level radioactive waste (LLRW) as defined in 10 CFR 61.
Waste, transuranic: material contaminated with transuranic elements that is produced primarily from reprocessing spent fuel and from use of plutonium in fabrication of nuclear weapons.
X rays: electromagnetic waves or photons not emitted from the nucleus, but normally emitted by energy changes in electrons. Energy changes occur in electron orbital shells that surround an atom or in the process of slowing down, in an x-ray machine.
