Absorbed Dose

The amount of energy imparted to matter by ionizing radiation per unit mass of irradiated material. (See Rad)


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


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

Alpha (a) Particle

An ionizing particle emitted from the nucleus of an atom 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). Strongly ionizing and weakly penetrating radiation.

Analytical Radiation Generating Equipment

A group or system of components which produce ionizing radiation as either a primary or a secondary result and is used to determine or alter properties of materials being measured or analyzed (e.g., electron microscopes, x-ray diffraction).

Annihilation (Electron)

An interaction between a positive and negative electron; their energy, including rest energy, being converted into electromagnetic radiation (annihilation radiation).


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

Atomic Number (Z)

The number of protons in the nucleus of a neutral atom of a nuclide.

Auto radiograph

Record of radiation from radioactive material in an object, made by placing the object in close proximity to a photographic emulsion.

Background Radiation

Ionizing radiation arising from a radioactive material other than the one directly under consideration. Background radiation from cosmic rays and natural radioactivity is always present. There may also be background radiation due to the presence of radioactive substances in other parts of the building and in the building material itself.

Beta (b) Particle

A charged particle emitted from the nucleus of an atom, having a mass and charge equal in magnitude to that of the electron.

Beta Ray

A stream of high-speed electrons or positrons of nuclear origin more penetrating but less ionizing than alpha rays.


Electromagnetic (x-ray) radiation associated with the deceleration of charged particles passing through matter. Usually associated with energetic beta emitters such as phosphorus-32.


Determination of variation from standard (accuracy) of a measuring instrument to ascertain necessary correction factors.


A quantity of non-radioactive material or non-labeled material of the same chemical composition as its corresponding radioactive-labeled counterpart. When mixed with the corresponding radioactive labeled material, so as to form a chemically inseparable mixture, the carrier permits chemical (and some physical) manipulation.


An adjective applied to one or more radionuclides of an element in minute quantity, essentially undiluted with stable isotope carrier.

Contamination, Radioactive

Deposition of radioactive material any place it is not desired. Radioactive contamination may be harmful as a source of exposure to people or invalidate an experiment or procedure.

Controlled Area

A defined area in which radioactive material is used or stored in a room, or where radiation-generating equipment is located, and a potential exposure to ionizing radiation exists.

Count (Radiation Measurements)

The indication of a device designed to enumerate ionizing events. A count may refer to a single detected event or to the total (counts) in a given period of time. The term is often erroneously used to designate a disintegration, ionizing event, or voltage pulse.

Critical Organ

Organic tissue that, if irradiated, will result in the greatest hazard to the health of the individual or progeny.

curie (Ci)

The quantity of any radioactive material where the number of disintegrations is 3.7 x 1010 per second.

Decay, Radioactive

The disintegration of the nucleus of an unstable nuclide by the spontaneous emission of charged particles and/or photons.

Direct Supervision

To personally observe or be located in the room or in the general vicinity of the room to respond to a situation involving all activities related to the use of radioactive material or radiation generating equipment. (See Supervision)

Disintegration, Nuclear

A spontaneous nuclear transformation (radioactivity) characterized by the emission of energy and/or mass from the nucleus.


A general term denoting the quantity of radiation or energy absorbed in a specified mass. For special purposes, the dose must be appropriately qualified (e.g., See radiation absorbed dose).


Instrument to detect and measure accumulated radiation exposure.

Dose Equivalent (DE)

A quantity used in radiation protection expressing all radiation on a common scale for calculating the effective absorbed dose. The unit of dose equivalent is the rem (radiation equivalent man), which is numerically equal to the absorbed dose in rads multiplied by certain modifying factors such as the quality factor, the distribution factor, etc.

Efficiency (Counters)

A measure of the probability that a count will be recorded when radiation is incident on a detector. Usage varies considerably so it is well to make sure which factors (window, transmission, sensitive volume, energy dependence, etc.) are included in a given case.


A negatively charged elementary particle which is a constituent of every neutral atom. Its unit of negative electricity equals 4.8 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.

Electron Volt (eV)

A unit of energy equivalent to the amount of energy gained by an electron in passing through a potential difference of 1 volt. Larger multiple units of the electron volt frequently used are keV (thousand electron volts); MeV (million electron volts).


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 sign 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.

Film Badge

A packet of photographic film used for the approximate measurement of radiation exposure for personnel monitoring purposes. The badge may contain two or more films of differing sensitivity and it may contain filters which shield parts of the film from certain types of radiation.

Filter (Radiology)


A sheet of material, usually metal, placed in a beam of radiation to remove, as far as possible, the less penetrating components of the beam.


A sheet of material of lower atomic number, relative to that of the primary filter, placed in the filtered beam of radiation to remove characteristic radiation produced by the primary filter.

Gamma (g) Ray

Penetrating short wavelength electromagnetic radiation of natural origin emitted from the nucleus of specific unstable atoms (range of energy from 10keV to 9 MeV). Identical to x-ray except for origin (x-rays are artificially produced).

Geiger-Mueller (G-M) Counter

Highly sensitive gas-filled probe and associated circuitry used for radiation detection and measurement.

Half-life, Biological

The time required for the body to eliminate one-half of an administered dose of any substance by the regular processes of elimination. Biological half-life is approximately the same for both stable and unstable nuclides of a particular element.

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-life, Radioactive

Time required for a radioactive material to lose 50 percent of its activity by decay. Each radionuclide has a unique half-life.

At = A0et OR At = A0(0.5)n

At = Activity remaining after interval of time, t.
A0 = Initial activity where t = 0.
e = The base of the natural log system, 2.71828...
λ = Decay constant, 0.693/Τ1/2.
T1/2 = Half-life of a radioactive element.
t = Elapsed time interval.
n = Number of half-lives elapsed.

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.

Inverse Square Law

The intensity of radiation at any distance from a point source varies inversely as the square of that distance. For example, if a radiation exposure is 100 R/hr (I1) at 1 foot from a source (d1), the exposure will be 25 R/hr (I2) at 2 feet (d2).

I1/I2 = d22/d12


Atomic particle, atom, or chemical radical bearing an electrical charge, either negative or positive.


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.

Ionization, Specific

The number of ion pairs per unit length of the path of ionizing radiation in a medium, e.g., per centimeter of air or per micron of tissue.

Ionizing Radiation

Any electromagnetic or particulate radiation capable of producing ions, directly or indirectly, in its passage through matter.


Exposure to radiation


Nuclides having the same number of protons in their nuclei (and the same atomic number) but having a different number of neutrons (and mass number). Nearly identical chemical properties exist between isotopes of a particular element.


Labeled Compound

A compound consisting, in part, of labeled molecules. By observations of radioactivity or isotopic composition, a labeled compound or its fragments may be followed through physical, chemical, or biological processes.


Light Amplification by Stimulated Emission of Radiation. The laser region is that portion of the spectrum which includes ultra-violet, visible light, and infrared.

Liquid Scintillation Counter

A device in which light flashes produced by ionizing radiation in a solvent cocktail are converted into electrical pulses by a photomultiplier tube.

Mass Number (A)

The number of nucleons (protons and neutrons) in the nucleus of an atom.

Maximum Permissible Dose (MPD)

Maximum dose of radiation which may be received by persons working with ionizing radiation which will produce no detectable damage over the normal lifespan.

Microcurie (μCi)

One millionth of a curie (3.7 x 104 disintegrations per second).

Millicurie (mCi) 

One-thousandth of a curie (3.7 x 107 disintegrations per second).

Monitoring, Area

Surveying and/or wipe testing a specific location, room, building, or equipment for radiation or radioactive contamination. 

Monitoring, Personnel

Surveying and/or wipe testing any body part, breath, excretions, or clothing of an individual for radiation or radioactive contamination. 

Monitoring, Radiological

Periodic or continuous determination of the amount of ionizing radiation or radioactive contamination present in an occupied region as a safety measure for purposes of health protection.


Elementary particle with a mass approximately the same as that of a hydrogen atom and electrically neutral. It has a half-life of minutes and decays in a free state into a proton and an electron.


A species of atom characterized by the constitution of its nucleus and specified by the number or protons (Z), number of neutrons (N), and energy content. To be regarded as a distinct nuclide, the atom must be capable of existing for a measurable time.


Particle equal in mass to the electron and having an equal but positive charge.

Protective Barriers (Shielding)

Radiation absorbing material (e.g., lead, concrete, plaster, plastic) that is used to reduce radiation exposure. Primary protective barriers are sufficient to attenuate the useful beam to the required degree. Secondary protective barriers are sufficient to attenuate stray or scattered radiation to the required degree.


General reference to a Proposal for Radioactive Material Use at Miami University that has been approved by the Radiation Safety Committee. A “Protocol” includes a Part A-Questionnaire, a Part B-Experimental Plan, and a Part C-Written Protocol.


Elementary nuclear particle with a positive electric charge equal numerically to the charge of the electron and a mass of 1.007277 mass units.

Quality Factor (QF)

The linear-energy-transfer-dependent factor by which absorbed doses are multiplied to obtain a quantity that expresses the effectiveness of the absorbed dose (on a scale for all ionizing radiation). Used for radiation protection purposes.


See Radiation Absorbed Dose.


  1. The emission and propagation of energy through space or through a medium in the form of waves (e.g., electromagnetic waves, sound pressure, elastic waves).
  2. The energy propagated through a medium as waves. The term “radiation” or “radiant energy” usually refers to electromagnetic radiation when unqualified and is commonly classified according to frequency as Hertzian, infrared, visible (light), ultra-violet, x-ray, and gamma ray.
  3. By extension, corpuscular emission, such as alpha and beta radiation, or rays of mixed or unknown type, as cosmic radiation.

Radiation Absorbed Dose (rad)

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

Radiation Areas

Locations where radiation levels might expose individuals to 5 millirem in any one hour at 30 cm or a dose in excess of 100 millirem in any five consecutive days.

Radiation Generating Equipment

Any manufactured product, device, machine, or system that can generate or emit ionizing radiation during operation. Does not include radiation from radioactive material, microwave ovens, televisions or computer monitors, electric lamps and other appliances that generate very low levels of radiation.


The chemistry of radioactive materials; the use of radionuclides in chemistry. 

Radiological Survey

Evaluation of radiation hazards relating to the production, use, or existence of radioactive material or other sources of radiation under a specific set of conditions. Surveys often include a physical evaluation of materials and equipment, a measurement or estimate of radiation quantities that may be involved, and interviews to acquire a sufficient level of knowledge about the procedures involved to predict hazards resulting from expected or possible changes in materials or equipment.


A nuclide with a ratio of neutrons to protons that places the nucleus in a state of instability. In an attempt to reorganize to a more stable state, a nuclide may undergo various types of re-arrangement that


The potential toxic effects of radioactive material introduced into the body via ingestion, absorption, or inhalation.

Relative Biological Effectiveness (RBE)

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 (Roentgen Equivalent Man)

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, distribution factor, and any other necessary modifying factors.

Roentgen (R)

The quantity of x- or gamma-radiation such that the associated corpuscular emission per 0.001293 grams of dry air produces ions carrying one electrostatic unit of quantity of positive or negative electricity. The roentgen is a unit of exposure.


Change of direction of subatomic particles or photons as a result of a collision or interaction.

Sealed Source

A radioactive source sealed in an impervious container which has sufficient mechanical strength to prevent contact with and dispersion of the radioactive material under the conditions of use and wear for which it was designed.


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.

Specific Activity

Total radioactivity of a given nuclide per gram of a compound, element, or radioactive nuclide.


To oversee all activities related the use of radioactive material or radiation producing devices. (See Direct Supervision)

Tracer, Isotopic

An isotope or unnatural mixture of isotopes of an element that may be incorporated into a sample to observe the course of that element, alone or in combination, through a chemical, biological, or physical process. Observations may be made by measurement of radioactivity or of isotopic abundance.

Thermoluminescent Dosimeter (TLD)

A dosimeter made of certain crystalline material which is capable of storing a fraction of absorbed ionizing radiation and releasing that energy in the form of visible photons when heated. The amount of light released can be used as a measure of radiation exposure.

Wipe Test (may be referred to as a Smear or Swipe Test)

A procedure to determine if the surface is contaminated with a loose radioactive material. A receptacle (e.g., disc of filter paper or cotton swab) is rubbed on a surface and is measured for radioactivity.


Penetrating electromagnetic radiation having wavelengths shorter than those of visible light, typically produced by bombarding a metallic target with fast electrons in a high vacuum. In nuclear reactions, photons originating in the nucleus are customarily referred to as gamma rays and those originating in the extranuclear part of the atom as x-rays. These rays are sometimes called roentgen rays after their discoverer, W.C. Roentgen.