Radiation Terms and Definitions
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.
Activation
The process of making a radioisotope by bombarding a stable element with neutrons, protons, or other types of radiation.
Agreement State
A state that has signed an agreement with the Nuclear Regulatory Commission under which the state regulates the use of byproduct, source, and small quantities of special nuclear material within that state.
Air sampling
The collection of samples to detect the presence of, and/or to measure the quantity of volatile or solid radioactive material, nonradioactive particulate matter, or various chemical pollutants in the air.
Airborne radioactivity area
A room, enclosure, or area in which airborne radioactive materials, composed wholly or partly of licensed material, exist. It exists in concentrations that (1) Exceed the derived air concentration limits or (2) Would result in an individual present in the area without respiratory protection exceeding, during the hours the individual is present in the area, 0.6 percent of the annual limit on intake or 12 derived air concentration-hours.
ALARA
Acronym for "As Low As Reasonably Achievable." It means making every reasonable effort to maintain exposures to ionizing radiation as far below the dose limits as practical. Be consistent with the purpose for which the licensed activity is undertaken, taking into account the state of technology, the economics of improvements in relation to state of technology, the economics of improvements in relation to benefits to the public health and safety, and other societal and socioeconomic considerations. These means are in relation to utilization of nuclear energy and licensed materials in the public interest.
Alpha particle
A positively charged particle ejected spontaneously from the nuclei of some radioactive elements. It is identical to a helium nucleus that has a mass number of 4 and an electric charge of +2. It has low penetrating power and a short range (a few centimeters in air). The most energetic alpha particle will generally fail to penetrate the dead layers of cells covering the skin and can be easily stopped by a sheet of paper. Alpha particles represent much more of a health risk when emitted by radionuclides deposited inside the body.
Background radiation
Radiation from cosmic sources; naturally occurring radioactive materials, including radon (except as a decay product of source or special nuclear material), and global fallout as it exists in the environment from the testing of nuclear explosive devices. It does not include radiation from source, byproduct, or special nuclear materials regulated by the Nuclear Regulatory Commission. The typically quoted average individual exposure from background radiation is 360 millirems per year.
Becquerel (Bq)
The unit of radioactive decay equal to one disintegration per second. The Becquerel is the basic unit of radioactivity used in the international system of radiation units, referred to as the “SI” units. 37 billion (3.7×1010) becquerels = 1 curie (Ci).
Beta particle
A charged particle emitted from a nucleus during radioactive decay, with a mass equal to 1/1837 that of a proton. A negatively charged beta particle is identical to an electron. A positively charged beta particle is called a positron. Exposure to large amounts of beta radiation from external sources may cause skin burns (erythema). Beta emitters can also be harmful if they enter the body. Thin sheets of metal or plastic may stop beta particles.
Bioassay
The determination of kinds, quantities, or concentrations and, in some cases, the locations of radioactive material in the human body, whether by direct measurement (in vivo counting) or by analysis and evaluation of materials excreted or removed (in vitro) from the human body
Biological half-life
The time required for a biological system, such as that of a human, to eliminate, by natural processes, half of the amount of a substance (such as a radioactive material) that has entered it.
Buildup factor
The factor by which the total value of the quantity being assessed at the point of interest exceeds the value associated with only primary radiation. The total value includes secondary radiations especially scattered radiation. The buildup factor is most commonly used for ionizing photons and may apply to various quantities—e.g., dose kerma, fluence.
Byproduct
Byproduct is (1) any radioactive material (except special nuclear material) yielded in, or made radioactive by, exposure to the radiation incident to the process of producing or using special nuclear material (as in a reactor); and (2) the tailings or wastes produced by the extraction or concentration of uranium or thorium from ore
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