Valuable Terminology
Absorbed Dose – The amount of ionizing radiation energy absorbed in matter, including human tissue. The units of absorbed dose are the rad and gray(Gy).
Activity – The rate of transformation (or ‘disintegration’ or ‘decay’) of radioactive material. The units of activity are the curie (Ci) and the bacquerel (Bq).
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.
Airborne Radioactivity Area – A room, enclosure, or area in which airborne radioactive materials exist in concentrations – (1) In excess of the specified derived air concentrations (DACs) and (2) To such a degree that an individual present in the area without respiratory protective equipment could exceed, during the hours an individual is present in a week, an intake of 0.6 percent of the annual limit on intake (ALI) or 12 DAC-hours.
ALARA (acronym for as low as is 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 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 radioactive 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 electrostatic charge of + 2.
Annual Limit on 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 rem (0.05 Sv) or a committed dose equivalent of 50 rem (0.5 Sv) to any individual organ or tissue. The ALI given by ICRP 1991 are based on limiting the committed effective dose from an intake in a single year to 20 mSv.
Atom – The smallest particle of an element that cannot be divided or broken up by chemical means. It consists of a central core called the nucleus, which contains protons and neutrons. Electrons revolve in orbits in the region surrounding the nucleus.
Atomic Number – The number of protons or (or number of positive charges) in the nucleus of an atom. The number of protons determines what an atom is chemically, and hence, identifies it as belonging to a certain chemical element.
Beta Particle – A negatively charged particle that is emitted by certain radioactive atoms. A beta particle is identical to the electron.
Becquerel – A unit, in the International System of Units (SI), of measurement of radioactivity equal to one transformation per second.
Bioassay (radiobioassay) – 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 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 the amount of a substance (such as a radioactive material) that has entered it.
Chronic Exposure – The absorption of radiation (or intake of radioactive materials over a long period of time, i.e., over a life time).
Committed Dose Equivalent (H T, 50) – The dose equivalent to organs or tissues of reference (T) that will be received from an intake of radioactive material by an individual during the 50-year period following intake. The ICRP defines this as the committed equivalent dose. The units of the committed dose equivalent are the rem or the sievert.
Committed Effective Dose (H E, 50) – The sum of the products of the weighing factors applicable to each of the body organs or tissues that are irradiated and the committed equivalent dose to these organs or tissues. The unit of committed effective dose is the sievert.
Committed Equivalent Dose (H T, 50) – The equivalent dose to organs or tissues of reference (T) that will be received from an intake of radioactive material by an individual during the 50-year period following the intake. The unit of committed equivalent dose is sievert.
Contamination – The deposition of unwanted radioactive material on the surfaces, areas, objects, or personnel.
Cosmic Radiation – Penetrating ionizing radiation, both particulate and electromagnetic, originating in space. Secondary cosmic rays, formed by interactions in the earth’s atmosphere, account for about 45 to 50 millirem annually.
Curie (Ci) – The basic unit of activity. A quantity of any radionuclide that undergoes an average transformation rate of 37 billion transformations per second. One curie is the approximate activity of 1 gram of radium. Named for Marie and Pierre Curie, who discovered radium in 1898.
Decay, Radioactive – The decrease in the amount of any radioactive material with the passage of time, due to spontaneous emission from the atomic nuclei of either alpha or beta particles, often accompanied by gamma radiation.
Declared Pregnant Woman – A woman who has voluntarily informed her employer, in writing, of her pregnancy and the estimated date of conception.
Decontamination – The reduction or removal of contaminating radioactive material from a structure, area, object, or person. Decontamination may be accomplished by (1) treating the surface to remove or decrease the contamination; or (2) letting the material stand so that the radioactivity is decreased as a result of radioactive decay.
Deep-dose equivalent (H d) – As defined by the NRC, the dose equivalent estimated for a tissue depth of 1 cm. The deep-dose equivalent applies to external whole-body exposure and is intended to represent the upper limit to the dose received by the major organs and tissues of the body other than skin and lens of the eye.
Delayed Health Effects – Radiation effects which are manifested long after the relevant exposure. The vast majority are stochastic, that is, the severity is independent of dose and the portability is assumed to be proportional to the dose, without threshold.
Derived air Concentration (DAC) – The concentration of a given radionuclide in air which, if breathed by the reference man for a working year of 2,000 hours under conditions of light work (inhalation rate 1.2 cubic meters of air per hour), results in an intake of one ALI.
Dose Equivalent (H T) – The product of the absorbed dose in tissue, quality factor, and all other necessary modifying factors at the location of interest. The units of dose equivalent are the rem and sievert (Sv). The ICRP defines this as the equivalent dose.
Effective Dose (E) – The sum over specified tissues of the products of the equivalent dose in a tissue (T) and the weighing factor for that tissue (W T), i.e., E = S W TH T.
Effective Dose Equivalent (H E) – The sum of products of the dose equivalent to the organ or tissue (H T) and the weighing factors (W T) applicable to each of the body organs or tissues that are irradiated (H E = S W TH T). The ICRP defines this as the effective dose.
Effective Half-life – The time required for the amount of a radioactive element deposited in a living organism to be diminished 50 percent as a result of the combined action of radioactive decay and biological elimination.
Electromagnetic Radiation – Energy being propagated by a traveling wave motion resulting from changing electric or magnetic fields. Familiar electromagnetic radiations range from x-rays and gamma rays of short wavelength, through the ultraviolet, visible and infrared regions, to radar, radio waves of relatively long wavelength. The ionizing electromagnetic radiations are gamma rays and x-rays.
Exposure – A measure of the ionization produced in air by x- or gamma radiation; the sum of electric charges on all ions of one sign produced in air when all electrons liberated by photons in a volume of air are completely stopped in air, divided by the mass of the air in the volume; units of exposure in air is the roentgen or coulomb per kilogram (SI units).
Exposure – Being exposed to ionizing radiation or to radioactive material.
External Contamination – Radioactive materials deposited on the outside of the body.
External Dose – The portion of the dose equivalent received from radiation sources
outside the body.
Film Badge – A pack of photographic film used for approximate measurement of radiation exposure for personnel monitoring purposes. The badge may contain two or the films of differing sensitivity, and it may contain a filter that shields part of the film from certain types of radiation.
Gamma Radiation or Gamma Rays – Gamma radiation is high-energy, short-wavelength electromagnetic radiation emitted from the nucleus. A gamma ray is a discrete packet of electromagnetic energy. Gamma radiation frequently accompanies alpha and beta emissions and always accompanies nuclear fissions. Gamma rays are very penetrating and are best stopped or shielded against by dense materials, such as lead or uranium. Gamma rays are identical to x-rays, but have a nuclear origin, rather than an atomic origin.
Geiger-Muller Counter – A radiation detection and measuring instrument. It consists of a gas-filled tube containing electrodes, between which there s an electrical voltage but no current flowing. When ionizing radiation passes through the tube, a short, intense pulse of current passes from the negative electrode to the positive electrode and is measured or counted. The number of pulse per second measures the intensity of radiation. It was named for the Hans Geiger and W. Muller who invented it in the 1920s. It is sometimes called simply a Geiger counter or a G-M counter.
Gray (Gy) – The SI unit of absorbed dose. One gray is equal to an absorbed dose of 1 J kg -1 (100 rad).
Half-life – The time in which half the atoms of a particular radioactive substance disintegrate to another nuclear form. Measured half-lives vary from millionth of a second to billions of years. Also called physical half-life.
Half-life, Biological – The time required for the body to eliminate half of the material taken in by natural biological means.
Half-life, Effective – The time required for a radionuclide contained in a biological system, such as a human or an animal, to reduce it’s activity by half as a combined result of radioactive decay and biological elimination.
Half-time, physical (T R) – The time taken for the activity of a radionuclide to lose half its value by radioactive decay.
Ion – An atom that has too many or too few electrons, causing it to be chemically active; an electron that is not associated (in orbit) with a nucleus.
Ion Pair – A pair of atoms or molecules, one with a negative charge and one with a positive charge.
Ionization – The process of adding one or more electrons to, or removing one or more electrons from, atoms or molecules thereby creating ions. High temperatures, electrical discharges, or nuclear radiations can cause ionization.
Ionizing Radiation – Any radiation capable of displacing electrons from atoms or molecules thereby producing ions. Examples: alpha, beta, gamma, x-rays and neutrons.
Isotope – One of two or more atoms with the same number of protons, but different numbers of neutrons, in their nuclei. Thus, carbon-12, carbon-13 and carbon-14 are isotopes of the element carbon, the number denoting the approximate atomic weights. Isotopes have very nearly the same chemical properties, but often different physical properties (for example, carbon-12 and -13 are stable, carbon-14 is radioactive.
Linear Energy Transfer (LET) – An expression of the energy lost by a charged particle per unit distance traveled in a material (in keV mm -1 or other units of energy and length). The value of LET is determined by the material and the type and energy of the charged particle. Effectiveness in producing a biological effect per unit absorbed dose (i.e., quality factor or Q) increases with the LET in tissue (or water). Electrons (and beta particles) and x and gamma rays (which produce electrons as their initial interactions in tissue) are referred to as ‘low’ LET radiations and have been assigned Q’s of 1.
Microcurie – A one-millionth part of curie.
Nanocurie – One billionth part of a curie.
NARM – Any Naturally occurring or Accelerator produced Radioactive Material. It does not include byproduct, source, or special nuclear material.
Occupational Radiation Exposure – The radiation exposure or dose to an individual in the course of employment in which the individual’s assigned duties involve exposure to radiation and to radioactive materials. Occupational dose does not include dose received from: background radiation, as a patient from medical practices; from voluntary participation in medical research programs; or as a member of the general public.
Pair production – An absorption process for x- or gamma-radiation in which the incident photon in annihilated in the vicinity of the nucleus of the absorbing atom with subsequent production of an electron and positron pair. The reaction only occurs for incident photon energies exceeding 1.02 MeV. This is an example of direct conversion of energy into matter according to Einstein’s equation: E = mc 2. It only occurs when a gamma-ray passes close to a nucleus which appears to act as a catalyst for the process.
Positron – Particle equal in mass, but opposite in charge, to the electron; a positive electron.
Proton – An elementary nuclear particle with a positive electric charge located in the nucleus of an atom.
Public Dose – The dose received by a member of the public from exposure to radiation and to radioactive material released by a license, or to another source of radiation either within a licensee’s controlled area or in unrestricted areas. It does not include occupational dose or doses received from background radiation, as patient from medical practices, or from voluntary participation in medical research programs.
Rad – The special unit of absorbed dose. One rad is equal to an absorbed dose of 0.01 kg -1 (0.01 gray).
Radiation (ionizing radiation) – Alpha particles, beta particles, gamma rays, x-rays, neutrons, high-speed electrons, high-speed protons, and other particles capable of producing ions. Radiation, as used in this part, does not include non-ionizing radiation, such as radio- or microwaves, or visible, infrared, or ultraviolet light.
Radiation Area – An area, accessible to individuals, in which radiation levels could result in an individual receiving a dose equivalent in excess of 0.005 rem (0.05 mSv) in 1 hour at 30 centimeters from the radiation source or from any surface that the radiation penetrates.
Radiation Controlled Area – An area inside a facility for which access is controlled, and for which special conditions may be prescribed, because of the potential for radiation, airborne radioactivity or radioactive contamination.
Radiation Shielding – Reduction of radiation by interposing a shield of absorbing material between any radioactive source and a person, work area or radiation-sensitive device.
Radioactive Contamination – Deposition of radioactive material in any place where it may harm persons or equipment.
Radiological Survey – The evaluation of the radiation hazards accompanying the production, use or existence of radioactive materials under a specific set of conditions. Such evaluation customarily includes a physical survey of the deposition of materials and equipment, measurements or estimates of the levels of radiation that may be involved, and a sufficient knowledge of processes affecting these materials to predict hazards resulting from unexpected or possible changes in materials or equipment.
Radon (Rn) – A radioactive element that is one of the heaviest gases known. Its atomic number is 86. Radon with a mass number of 222, is a daughter of radium-226.
Rem – The special unit of any of the quantities expressed as dose equivalent. The dose equivalent in rem is equal to the absorbed dose in rad multiplied by the quality factor (1 rem = 0.01 sievert).
Restricted Area – An area, access to which is limited by the licensee for the purpose of protecting individuals against undue risks from exposure to radiation and radioactive materials. Restricted area does not include areas used as residential quarters, but separate rooms in a residential building may be set apart as restricted area.
Sanitary sewerage – A system of public sewers for carrying off waste water and refuse, but excluding sewage treatment facilities, septic tanks, and leach fields owned or operated by the licensee.
Scintillation Detector or Counter – The combination of phosphor, photomultiplier tube, and associated electronic circuits for counting light emissions produced in the phosphor by ionizing radiation.
Shielding – Any material or obstruction that absorbs radiation and thus tends to protect personnel or materials from the effects of ionizing radiation.
Sievert – The SI unit of any of the quantities expressed as dose equivalent. The dose equivalent in sieverts is equal to the absorbed dose in gray multiplied by the quality factor (1 Sv = 100 rem).
Smear or Smear Test – A method of determining the removable contamination on a surface. The suspected area is wiped with a filter paper and the radioactivity in the paper is measured. Also called a wipe test.
Somatic Effects of Radiation – Effects of radiation limited to the exposed individual, as distinguished from genetic effects, which may also affect subsequent unexposed generations.
Survey – An evaluation of the radiological conditions and potential hazards incidents to the production, use, transfer, release, disposal, or presence of radioactive material or other sources of radiation. When appropriate, such an evaluation includes a physical survey of the location of radioactive material and measurements or calculations of levels of radiation, or concentrations or quantities of radioactive material present.
Survey Meter – Any portable radiation detection instrument especially adapted for inspecting an area to establish the existence and amount of radioactive material present.
Unstable Atom – An atom that will spontaneously transform to another atom (radioactive).
Unrestricted area – An area, access to which is neither limited nor controlled by the licensee.
