Absorbed dose: The amount of energy given up to matter by ionizing radiation per unit mass of irradiated material. The rad and the gray (SI) are units of absorbed dose.
Activity: The number of nuclear disintegrations occurring in a given quantity of material per unit time. The Curie and the Becquerel (SI) are the units of activity.
ALARA: A philosophy and system of dose limitation based on keeping doses As Low As Reasonably Achievable, economic and social factors being taken into account.
Alpha particle: A densely ionizing particle emitted from the nucleus during radioactive decay, having a mass and charge equal in magnitude to a helium nucleus (two protons and two neutrons).
Attenuation: The reduction of radiation field intensity caused by the interaction of particles or electromagnetic radiation with matter. Usually refers to energy lost in shielding used for radiation protection.
Becquerel: The SI unit of radioactivity. One Becquerel is equal to one disintegration per second.
Beta particle: Charged particle emitted from the nucleus during radioactive decay, having a mass and charge equal to that of an electron.
Bioassay: The collection and analysis of human tissue or excreta to determine the amount of radioactive material that has been taken into the body.
Body burden (maximum permissible): That amount of radioisotope deposited in the body which will result in the dose limit to the critical organ (if the level remains constant).
Contamination, radioactive: A radioactive substance dispersed in materials or places where it is undesirable.
Critical organ: That organ in the body which concentrates deposited radioactive material and therefore receives the most dose and damage.
Curie (Ci): The unit of radioactivity equal to a rate of 3.7 E+10 nuclear disintegrations per second (2.22 E+12 dpm or 3.7E+10 Bq). Originally based on the radioactive decay rate of 1 gram of radium, discovered by Marie and Pierre Curie in 1898.
Daughter products: Nuclides that are formed by the radioactive decay of some other nuclide. In the case of radium-226, for example, there are 10 successive daughter products, ending in the stable isotope lead-206.
Decay, radioactive: Disintegration of the nucleus of an unstable nuclide by the spontaneous emission of charged particles and/or photons.
Dose equivalent: A quantity used for radiation protection purposes that expresses on a common scale for all radiations, the irradiation incurred by exposed persons. It is defined as the product of the absorbed dose, the quality factor, and any other modifying factors. The rem and the sievert (SI) are units of dose equivalent.
Dose rate: Radiation dose expressed as a dose absorbed per unit time, for example - mRem/hr. Dose rate is usually expressed as whole body (see: Radiation, penetrating). If the dose rate is not whole body, there must be an indication of distance from the radiation source, for example - at 1 cm.
Dosimeter: A portable instrument for measuring and registering the accumulated dose of ionizing radiation.
Electromagnetic radiation: A traveling wave motion resulting from changing electric or magnetic fields. Familiar electromagnetic radiations range from gamma and x-rays of short wavelength, through the ultraviolet, visible and infrared regions, to radar and radio waves of relatively long wavelength.
Electron: A light elementary particle with a negative charge. High energy electrons traveling free of the atom are called beta particles.
EH&S: Environment Health & Safety.
Exposure: A measure of the ionization (charge) produced in a unit volume of air by x or gamma radiation. The Roentgen (R) is a unit of exposure. The SI system expresses exposure in coulombs/kilogram.
External radiation: Exposure to ionizing radiation when the radiation source is located outside the body. Not to be confused with Internal Radiation, where the radiation source has been deposited inside the body.
Gamma ray: Penetrating electromagnetic radiation of nuclear origin. Except for its origin and usually higher energy, it is identical to an x-ray.
Genetic effects: Mutations in chromosomes and genes that are passed on to future generations.
G-M or GM: Geiger-Mueller - a type of ionization detector used to detect beta, gamma, and X-rays. Named for the two scientists credited with developing the G-M tube.
Half-life, biological: The time required for a material in the body to be diminished by 50% as a result of biological elimination.
Half-life, effective: The time required for a radioactive element in the body to be diminished by 50% as a result of the combined action of radioactive decay and biological elimination.
Half-life, physical: The time in which half the atoms of a particular radioactive substance disintegrate to another nuclear form. Measurements vary from millionths of a second to billions of years.
Half-value layer: The thickness of a specified substance which, when introduced into the path of a beam of radiation, reduces the exposure rate by one-half. Normally applied only to electromagnetic radiation (gamma or x-rays).
Ionization: The process by which a neutral atom or molecule acquires either a positive or negative charge.
Ionizing radiation: Any electromagnetic or particulate radiation capable of producing ions (either directly or indirectly) in its passage through matter.
Isotope: One of two or more atoms with the same number of protons, but different numbers of neutrons in their nuclei. Isotopes of the same element have very nearly the same chemical properties.
LET: Linear energy transfer. The energy imparted per unit length of transversed medium.
Micro-(µ): A prefix that divides a basic unit into one million parts. Often used with activity, such as microcurie (2.22 E+6 dpm = 1 µCi).
Milli-(m): A prefix that divides a basic unit by 1000. Often used with dose and activity, such as millirem or millicurie (2.22 E+9 dpm = 1 mCi).
Neutron: Elementary particle with a mass approximately the same as that of a proton and is electrically neutral.
Nucleus: The small, central, positively charged region of an atom that carries essentially all the mass.
Nuclide: A species of atom having a specified number of neutrons and protons in its nucleus.
Quality factor: A multiplying factor expressing the relative effectiveness in causing biological damage of any type of radiation based on its LET. Used with absorbed dose to express dose equivalent.
ORS: The Office of Radiation Safety.
Proton: Elementary particle with a mass approximately the same as that of a hydrogen atom and electrically positive.
Rad: A unit of absorbed dose. The word comes from the acronym radiation absorbed dose, and is equivalent to 100 ergs per gram. It does not take into account the biological effect resulting from the absorbed dose.
Radiation, non-penetrating: Radiation incapable of penetrating and causing damage to interior organs. Includes alpha and beta particles, very low energy x-rays and very low energy gammas.
Radiation, penetrating: Radiation capable of causing damage to internal as well as external parts of the body. Includes x-rays and gammas.
Radioactive: Exhibiting radioactivity or pertaining to radioactivity.
Radioactivity: The spontaneous emission of radiation (alpha, beta, gamma rays, or neutrons) from an unstable nuclide.
RAM: Short for Radio Active Material(s).
Radioisotope: An unstable isotope of an element that decays or disintegrates spontaneously, emitting radiation.
Rem: A unit of dose equivalent. The word comes from the acronym, roentgen equivalent man and takes into account the biological effect from an absorbed dose of radiation.
Roentgen-(R): The unit for exposure. It is equal to the amount of gamma or x-rays required to produce ions carrying 1 electrostatic unit of electrical charge in 1 cubic centimeter of dry air under standard conditions.
Somatic effects, radiation: Effects of radiation limited to the exposed individual, as distinguished from genetic effects, which may also affect subsequent unexposed generations.
Specific activity: The number of Curies per gram of material. Specific activity is a function of half-life, and is therefore also unique to each radionuclide.
TLD: Thermoluminescent dosimeter - a type of dosimeter.
X-Rays: Penetrating electromagnetic radiations of orbital origin, resulting from radioactive decay by electron capture and internal conversion processes. Usually artificially produced by bombardment of a metallic target with fast electrons in a vacuum.