ACTIVATION: The process by which neutrons bombard stable atoms to make them radioactive.
ACTIVITY: A measure of how radioactive a particular radioisotope is. Activity is calculated by the number of atoms
disintegrating per unit of time. Its unit of measurement is the curie. See SPECIFIC ACTIVITY.
ACUTE RADIATION SYNDROME (RT): The immediate effects of a short-term whole-body over exposure of a person
to ionizing radiation. These effects include nausea and vomiting, malaise increased temperature, and blood changes.
ADDED FILTER: Filter added to the inherent filtration.
ADDITIVE, ABSORPTIVE (RT): See CONTRAST AGENT.
ADHERENCE: The extent to which a coating bonds to a substrate.
ADHERENCE INDEX: The measure of the adherence of porcelain enamel and ceramic coatings to sheet metal
ADHESION: The adhering or sticking together of substances in contact with each other.
AERIAL IMAGE (RT): The representation (in relief) of the distribution of the intensity of the radiation in the plane of
the radiograph (plane of the film).
AFTERGLOW (RT): The persistence of light emission from an intensifying screen or fluorescent screen after an
exposure. It is a form of phosphorescent radiation.
AGE HARDENING: Increasing the hardness and possible strength of an alloy by a relatively low-temperature heat
treatment that causes precipitation of components or phases of the alloy from the supersaturated solid solution. Also
known as precipitation hardening.
AGGLOMERATION (PT) (MT): An indiscriminately formed mass. A cluster of disparate elements.
AGING: A metallurgical change in a metal alloy resulting in an increase in mechanical properties. This change can
occur in some instances at room temperatures. More often its effects are increased by holding for specified lengths of
time at elevated temperatures. Also known as precipitation hardening.
AIR-COOLED TUBE (RT): An X-ray tube for which the principal method of cooling is dissipation of heat into
AIRCRAFT QUALITY STEEL: Steel produced in such a way as to be as nearly free of discontinuities as possible.
AIR GAP (MT): When a magnetic circuit contains a small gap that the magnetic flux must cross, the space is referred
to as an air gap. Cracks produce small air gaps on the surface of a magnetized part.
AIR HOLE: A hole in a casting caused by air or gas trapped in the metal during solidification; also, Gas Hole
AIR SCATTER (RT): Ionizing radiation that, because of a scattering interaction with air, arrives at a point by way of
an indirect route instead of arriving directly from the source.
ALARA: (acronym for as low as is reasonably achievable") means making every reasonable effort to maintain
exposures to radiation as far below dose limits as is practical consistent with the purposes for which the radiation
exposure is received, taking into account the state of technology, the economics of improvements in relation to benefits
to the public health and safety, and other societal and socioeconomic considerations, and in relation to utilization of
radiation in the public interest.