Radiation Safety Manual Glossary - (A)

Absorbed Dose

the amount of energy imparted to matter by ionizing radiation per unit mass of irradiated material. The unit of absorbed dose is the rad, which is 100 ergs/gram.

Absorption

the phenomenon by which radiation imparts some or all of its energy to any material through which it passes.

Activation

the process of making a material radioactive by bombardment with neutrons, protons, or other nuclear radiation.

Activity

the number of nuclear disintegrations occurring in a given quantity of material per unit time.

Acute Exposure

the absorption of a relatively large amount of radiation (or intake of radioactive material) over a short period of time.

Acute Health Effects

prompt radiation effects (those that would be observable within a short period of time) for which the severity of the effect varies with the dose, and for which a practical threshold exists.

Adult

an individual 18 or more years of age.

ALARA

(acronym for As Low As Reasonably Achievable) making every reasonable effort to maintain exposures to radiation as far below the dose limits as is practical 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, and in relation to utilization of nuclear energy and licensed materials in the public interest.

Alpha Particle

a strongly ionizing particle emitted from the nucleus during radioactive decay having a mass and charge equal in magnitude to a helium nucleus, consisting of 2 protons and 2 neutrons with a double positive charge.

Alpha Ray

a stream of fast moving helium nuclei (alpha particles), a strongly ionizing and weakly penetrating radiation.

Anion

a negatively charged ion.

Annual Limit of Intake (ALI)

the derived limit for the amount of radioactive material taken into the body of an adult worker by inhalation or ingestion in a year. ALI is the smaller value of intake of a given radionuclide in a year by the reference man that would result in a committed effective dose equivalent of 5 rems (0.05 Sv) or a committed dose equivalent of 50 rems (0.5 Sv) to any individual organ or tissue.

Atom

smallest particle of an element which is capable of entering into a chemical reaction.

Attenuation

the process by which a beam of radiation is reduced in intensity when passing through some material. It is the combination of absorption and scattering processes and leads to a decrease in flux density of the beam when projected through matter.