Radiation Terms and Definitions
This page provides a list of general terms that are used to describe aspects of radiation science. Click on the desired term from the list to retrieve the definition for the term.Kilo-
A prefix that multiplies a basic unit by 1,000 or 103.
Low-level waste
Low-level radioactive waste (LLW) is a general term for a wide range of wastes. Industries, hospitals and medical, educational, or research institutions; private or government laboratories; and nuclear fuel cycle facilities (e.g., nuclear power reactors and fuel fabrication plants) using radioactive materials generate low-level wastes as part of their normal operations. These wastes are generated in many physical and chemical forms and levels of contamination.
Mega-
prefix that multiplies a basic unit by 1,000,000 or 106.
Megacurie
One million (106) curies.
Micro-
A prefix that divides a basic unit into one million parts (10-6).
Microcurie
One millionth (10-6) of a curie.
Mill tailings
Naturally radioactive residue from the processing of uranium ore into yellowcake in a mill. Although the milling process recovers about 93 percent of the uranium, the residues, or tailings, contain several naturally occurring radioactive elements, including uranium, thorium, radium, polonium, and radon.
Milli-
A prefix that divides a basic unit by 1,000 (10-3).
Millirem
One thousandth of a rem. (1 mrem = 10-3 rem)
Molecule
A group of atoms held together by chemical forces. A molecule is the smallest unit of a compound that can exist by itself and retain all of its chemical properties.
Nano-
A prefix that divides a basic unit by one billion (10-9).
Nanocurie
One billionth (10-9) of a curie.
Natural uranium
Uranium as found in nature. It contains about 0.7 percent uranium-235, 99.3 percent uranium-238, and a trace of uranium-234.
Neutron
An uncharged elementary particle with a mass slightly greater than that of the proton, and found in the nucleus of every atom heavier than hydrogen.
Neutron capture
process in which an atomic nucleus absorbs or captures a neutron.
Noble gas
A gaseous chemical element that does not readily enter into chemical combination with other elements. An inert gas. Examples are helium, argon, krypton, xenon, and radon.
Nonstochastic effect
Health effects, the severity of which varies with the dose and for which a threshold is believed to exist. Nonstochastic effects generally result from the receipt of a relatively high dose over a short time period. Skin erythema (reddening) and radiation-induced cataract formation is an example of a nonstochastic effect. This term has been replaced with Deterministic Effect.
NORM
An acronym for Naturally Occurring Radioactive Material. Naturally occurring radioactive materials are common in virtually all rocks, minerals, and soils. They naturally contain small amounts of uranium, thorium, and a radioactive isotope of potassium. Plants and animals are also naturally radioactive; they contain small (but measurable) levels of radioactive potassium as well as radioactive carbon (C-14) and hydrogen (tritium, or H-3) that are formed by cosmic ray interactions in the atmosphere.
Nuclear energy
The energy liberated by a nuclear reaction (fission or fusion) or by radioactive decay.
Nuclear force
A powerful short-ranged attractive force that holds together the particles inside an atomic nucleus.
Nuclear power plant
An electrical generating facility using a nuclear reactor as its power (heat) source.
Nucleus
The small, central, positively charged central core of an atom. Except for the nucleus of ordinary (light) hydrogen, which has a single proton, all atomic nuclei contain both protons and neutrons. The number of protons determines the total positive charge, or atomic number, which in turn determines the chemical element that a given atom represents. That is to say, all atoms of a given chemical element have the same number of protons in their nuclei. The total number of neutrons and protons is called the mass number.
Nuclide
A general term that refers to any known isotope, either stable or unstable, of any element. Whereas a single element can have isotopes, when referring to the isotopes of more than one element, the proper term is nuclide. A radionuclide is an unstable nuclide.
Parent
A radionuclide that upon radioactive decay or disintegration yields a specific nuclide (the decay product or daughter).
Periodic table
An arrangement of chemical elements in order of increasing atomic number. Elements of similar properties are placed one under the other yielding groups or families of elements. Within each group, there is a variation of chemical and physical properties but, in general, there is a similarity of chemical behavior within each group.
Personnel monitoring
The use of portable survey meters to determine the presence or amount of radioactive contamination on an individual, or the use of a dosimeter to determine an individual's radiation dose.
Photon
A quantum (or packet) of energy emitted in the form of electromagnetic radiation. Gamma rays and x rays are examples of photons.
Pico-
A prefix that divides a basic unit by one trillion (10-12).
Picocurie
One trillionth (10-12) of a curie.
Plutonium (Pu)
A heavy, radioactive, man-made metallic element with atomic number 94. Its most important isotope is fissile plutonium-239 which is produced by neutron irradiation of uranium-238, followed by a two-step decay. It exists in only trace amounts in nature.
Pocket dosimeter
A small ionization detection instrument worn by an individual that directly measures the ionizing radiation exposure.
Proportional counter
A radiation instrument in which an electronic detection system receives pulses that are proportional to the number of ions formed in a gas-filled tube by ionizing radiation.
Proton
An elementary nuclear particle located in the nucleus of an atom. The proton has a single positive electric charge.
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