Definitions and Acronyms
A
Absorption: The phenomenon by which radiation imparts some or all of its energy to any material through which it passes.
Activity: The number of nuclear disintegrations occurring in a given quantity of material per unit time. (See Curie.)
ALARA: Acronym for the phrase “as low as is reasonably achievable,” which embodies general regulatory philosophy pertaining to exposure of personnel to ionizing radiation.
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.
Annihilation (Electron): An interaction between a positive and negative electron (or other particle, anti-particle pair) wherein their energy, including rest energy, is converted into electromagnetic radiation (annihilation radiation).
Personnel Monitoring: Monitoring any part of an individual, his breath, excretions, or any part of his clothing. (See Radiological Survey.)
Atom: Smallest particle of an element which is capable of entering into a chemical reaction.
Autoradiograph: Record of radiation from radioactive material in an object, made by placing the object in close proximity to a photographic emulsion.
B
Becquerel: SI unit of activity, abbreviated Bq. 1 Bq = 1 disintegration/sec.
Beta Particle: Charged particle emitted from the nucleus of an atom, having a mass and charge equal in magnitude to that of the electron.
Bremsstrahlung: Electromagnetic (x-ray) radiation associated with the deceleration of charged particles passing through matter. Usually associated with energetic beta emitters, e.g., phosphorus-32.
C
Contamination, Radioactive: Deposition of radioactive material in any place where it is not desired, and particularly in any place where its presence may be harmful. The harm may be in vitiating the validity of an experiment or a procedure, or in actually being a source of excessive exposure to personnel.
Carrier Free: An adjective applied to one or more radioactive isotopes of an element in minute quantity, essentially undiluted with stable isotope carrier.
Count (Radiation Measurements): The external indication in a device designed to enumerate ionizing events. It may refer to a single detected event or to the total registered in a given period of time. The term is often erroneously used to designate a disintegration, ionizing event, or voltage pulse.
Curie: The quantity of any radioactive material in which the number of disintegrations is 3.700 x 1010 per second. Abbreviated Ci.
D
Dose: A general term denoting the quantity of radiation or energy absorbed in a specified mass. For special purposes it must be appropriately qualified, e.g., absorbed dose.
E
Electron: Negatively charged elementary particle which is a constituent of every neutral atom. Its unit of negative electricity equals 4.8 x 10-10 electrostatic units or
1.6 x 10-19 coulombs. Its mass is 0.00549 atomic mass units.
Electron Capture: A mode of radioactive decay involving the capture of an orbital electron by its nucleus. Capture from the particular electron shell is designated as
“K-electron capture,” “L-electron capture”, etc.
Exposure: A measure of the ionization produced in air by x or gamma radiation. It is the sum of the electrical charges on all ions of one sig produced in air when all electrons liberated by photons in a volume element of air are completely stopped in air, divided by the mass of air in the volume element. The special unit of exposure is the roentgen.
F
Filter (Radiology), Primary: A sheet of material, usually metal, placed in a beam of radiation to remove, inasmuch as possible, the less penetrating components of the beam.
G
Geiger-Mueller (G-M) Counter: Highly sensitive gas-filled detector and associated circuitry used for radiation detection and measurement.
Genetic Effect of Radiation: Inheritable changes, chiefly mutations, produced by the absorption of ionizing radiations. On the basis of present knowledge these effects are purely additive, and there is no recovery.
H
Half-Life, Effective: Time required for a radioactive nuclide in a system to be diminished 50 percent as a result of the combined action of radioactive decay and biological elimination.
Effective half-life = Biological half-life x Radioactive half-life
Biological half-life + Radioactive half-life
Half Value Layer (Half thickness): The thickness of any specified material necessary to reduce the intensity of an x-ray or gamma ray beam to one-half its original value.
Health Physics: A term in common use for that branch of radiological science dealing with the protection of personnel from harmful effects of ionizing radiation.
I
Ion: Atomic particle, atom, or chemical radical bearing an electrical charge, either positive or negative.
Ionization: The process by which a neutral atom or molecule acquires either a positive or a negative charge.
Ionization Chamber: An instrument designed to measure the quantity of ionizing radiation in terms of the charge of electricity associated with ions produced within a defined volume.
Ionizing Radiation: Any electromagnetic or particulate radiation capable of producing ions, directly or indirectly, in its passage through matter.
Isotopes: Nuclides having the same number of protons in their nuclei, and hence having the same atomic number, but differing in the number of neutrons, and therefore in the mass number. Almost identical chemical properties exist among isotopes of a particular element.
L
M
Milliroentgen (mR): A sub-multiple of the roentgen equal to one one-thousandth (1/1000th) of a roentgen. (See Roentgen.) (“mR” also is used for “millirad.”)
Millicurie: One-thousandth of a curie (3.7 x 107 disintegrations per second), abbreviated mCi. Microcurie: One millionth of a curie (3.7 x 104 disintegrations per second), abbreviated µCi. Picocurie: One millionth of a microcurie
(3.7 x 10-2 disintegrations per second or 2.22 disintegrations per minute), abbreviated pCi.
N
Nuclide: A species of atom characterized by its mass number, atomic number, and energy state of its nucleus, provided that the atom is capable of existing for a measurable time.
P
Protective Barriers, Primary: Barriers sufficient to attenuate the useful beam to the required degree.
Protective Barriers, Secondary: Barriers sufficient to attenuate stray or scattered radiation to the required degree.
R
- The emission and propagation of energy through space or through a material medium in the form of waves; for instance, the emission and propagation of electromagnetic waves, or of sound and elastic waves.
- The energy propagated through a material medium of waves; for example, energy in the form of electromagnetic waves or of elastic waves. The term, “radiation” or “radiant energy,” when unqualified, usually refers to electromagnetic radiation. Such radiation commonly is classified according to frequency as Hertzian, infrared, visible (light), ultra-violet, x-ray, and gamma ray.
- By extension, corpuscular emissions, such as alpha and beta radiation, or rays of mixed or unknown type, such as cosmic radiation.
Radioactive Material: Any material (solid, liquid, or gas) which emits radiation spontaneously.
Radioactive Materials Laboratory: A volume bounded by a floor, a ceiling, and at least four floor-to-ceiling walls or partitions, in which radioactive materials are used or stored.
Radiological Survey: Evaluation of the radiation hazards incident to the production, use or existence of radioactive materials or other sources of radiation under a specific set of conditions. Such evaluation customarily includes a physical survey of the disposition of materials and equipment, measurements or estimates of the levels of radiation that may be involved, and a sufficient knowledge of processes using or affecting these materials to predict hazards resulting from expected or possible changes in materials or equipment.
Relative Biological Effectiveness (RBE): For a particular living organism or part of an organism, the ratio of the absorbed dose of a reference radiation that produces a specified biological effect to the absorbed dose of the radiation of interest that produces the same biological effect.
REM: The special unit of dose equivalent. The dose equivalent in rems is numerically equal to the absorbed dose in rads multiplied by the quality factor.
Roentgen (R): The quantity of x or gamma radiation such that the associated corpuscular emission per 0.001293 grams of dry air produces, in air, ions carrying one electrostatic unit of electrical charge of either sign. The roentgen is the special unit of exposure.
Scintillation Counter: A counter in which light flashes produced in a scintillator by ionizing radiation are converted into electrical pulses by a photomultiplier tube.
S
Shielding Material: Any material which is used to absorb radiation and thus effectively reduce the intensity of radiation, and in some cases, eliminate it. Lead, concrete, aluminum, water, and plastic are examples of commonly used shielding material.
Smear (Smear, Swipe or Wipe Test): A procedure in which a swab, e.g., a circle of filter paper, is rubbed on a surface and its radioactivity measured to determine if the surface is contaminated with removable radioactive material.
Specific Activity: Total radioactivity of a given nuclide per unit mass or per unit volume of a compound, element, or nuclide.