Glossary of Radiation Safety Terminology

Absorbed dose:  The energy imparted to matter by ionizing radiation per unit mass of irradiated material at the place of interest. The units of absorbed dose are the rad and the Gray (Gy).  1 Gy = 100 rad

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

Activity:  The rate of disintegration, transformation or decay of radioactive material.  Activity is expressed in the SI unit of Becquerel (Bq) or in the special unit of curie (Ci), or the multiples of either unit, or disintegrations or transformations per unit of time as follows:  One Becquerel (Bq) equals one disintegration or transformation per second (dps or tps); and One Curie (Ci) equals 3.7 x1010 disintegrations or transformations per second (dps or tps).  One curie also equals 3.7 x 1010 Becquerel (Bq).

Acute Exposure:  The absorption of a relatively large amount of radiation (or intake of radioactive material) over a short period of time.

Agreement State:  Any state in which the U.S. Nuclear Regulatory Commission -- a federal agency -- has agreed to allow the licensing of radioactive material to be governed by a state.  This is only allowed if the state regulations are at least as restrictive as the federal ones.  Kansas is an agreement state and regulates the safe uses of radiation and by-product material within its boundary.

Airborne Radioactive Material:  Radioactive material dispersed in the air in the form of dusts, fumes, mists, vapors, or gases.

ALARA:  Stands for "As Low As Reasonably Achievable" and is a regulatory requirement stating that the radiation worker and the Licensee will make every reasonable effort to keep radiation exposures as far below the dose limits specified in regulations as is practical, consistent with the purpose for which the licensed or registered activity is undertaken, taking the following into account:  (1) the state of technology, (2) the economics of improvements with respect to the state of the technology, (3) the economics of improvements in relation to benefits to public health and safety and to other societal and socioeconomic considerations; and (4) the economics of improvements with respect to the utilization of nuclear energy and licensed or registered sources of radiation in the public interest.

Attenuation:  The process by which radiation is reduced in intensity when passing through some material.

Authorized User:  A radiation permit holder; a faculty member (or other designated person) who has been approved by the Radiation Safety Committee for the possession and use of radioactive materials.

Background Radiation:  The radiation from non-occupational sources encountered in everyday life.  This includes many sources: cosmic radiation, naturally occurring radioactive materials including radon, uranium and thorium radioisotopes, Consumer products like smoke detectors, certain lantern mantles, and even some antique glassware and ceramics, etc.  Please see our webpage describing this in more detail.

Becquerel (Bq):  The SI unit of activity.  One Becquerel equals one disintigration per second (dps) -- also referred to as one transformation per second (tps).

Beta Particle:  A charged particle emitted from the nucleus of a atom during radioactive decay.  A negatively charged beta particle is identical to an electron.  A positively charged beta particle is called a positron.

Bioassay:  A method of measuring radioactivity in tissues.  The measurement may be to determine the types, quantities or concentrations, and in some cases, locations of the radioactive materials within the body.  This may be done by direct measurement (in vivo counting) or by analysis or materials excreted or removed from the body.

Bremmstrahlung:  X-ray radiation produced when charged particles pass through dense materials -- for example when P-32 is shielded with lead.  It is also the method by which x-rayd devices operate.

Chronic Exposure:  The absorption of radiation (or intake of radioactive material) over a long period of time.

Contamination:  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 caused may be a source of excessive exposure to personnel or the validity of an experiment or a procedure.

Committed Dose Equivalent (CDE):  The dose equivalent to organs or tissues of reference that will be received from an intake of radioactive material by an individual during the 50 year period following the intake. (units = Sievert or-Rem)):

Committed Effective Dose Equivalent (CEDE):  The sum of the products of the weighting factors applicable to each of the body organs or tissues that are irradiated and the committed dose equivalent to these organs or tissues (units = Sievert- or Rem))

CPM or cpm:  Counts per minute

Critical Organ:  The organ or tissue that when irradiated will result in the greatest hazard to the health of the individual or the individual's descendents.

Curie (Ci):  Unit of activity. One Curie (Ci) is the quantity of radioactive material that decays at the rate of 3.7 x 1010 transformations per second (tps). One Curie = 3.7 x 1010 Becquerels = 2.22 x 1012 disintegrations per minute. Commonly used submultiples of the Curie are the millicurie and the microcurie. One millicurie (mCi) = 0.001 Curie = 3.7 x 107 tps. One microcurie (µCi) = 0.000001 Curie = 3.7 x 104 tps.

Decay:  With respect to radioactive materials, this is the spontaneous transformation of an unstable atomic nucleus into a more stable one, in which radiation is released in the form of alpha particles, beta particles, gamma rays, and other particles. The rate of decay is measured in terms of its half-life.

Declared Pregnant Woman:  A woman who has voluntarily informed her employer, in writing, of her pregnancy and the estimated date of conception or of delivery. The written declaration shall remain in effect until the declared pregnant woman withdraws the declaration in writing or is no longer pregnant.

Deep Dose Equivalent: The dose equivalent to a tissue depth of 1 cm (1000 mg per cm2); applies to external whole body exposure.

Dose:  The amount of radiation to which something has been exposed or the amount that has been absorbed by a given mass of material, especially with respect to living tissue. A Dose is a generic term that means the absorbed dose, dose equivalent, effective dose equivalent, committed dose equivalent, committed effective dose equivalent, total organ dose equivalent, total organ dose equivalent, or total effective dose equivalent.

Dose Rate:  The radiation dose delivered per unit of time. For example, measured in Gy/hr or rad/hr.

Dosimeter:  A portable device for measuring and registering the total accumulated exposure to ionizing radiation (see Dosimetry and Radiation Monitoring Device).  Also referred to as an exposure monitoring badge

dpm:  Disintegrations per minute

Dose Equivalent:  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).

Effective Dose Equivalent (EDE):   The sum of the products of the dose equivalent to the organ or tissue and the weighting factors applicable to each of the body organs or tissues that are irradiated.

Efficiency:  The percent of total activity present for a given nuclide detected by the radiation detection instrument being used.  It is calculated by the following formula

((cpm - background)/dpm)(100%) = efficiency

External Dose:  That portion of the dose equivalent received from radiation sources outside the body.

Extremity:  Hand, elbow, arm below the elbow, foot, knee, or leg below the knee.

Geiger-Müller (G-M) meter:  Radiation detection and measuring instrument.  It consists of a gas-filled tube containing electrodes, between which there is 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 pulses per second measures the intensity of radiation.

Gray (Gy):  SI unit of absorbed dose.  One gray is equal to an absorbed dose of one joule per kilogram.  One gray is also equal to 100 rads.

Half-Life:  Time required for a radioactive substance to lose 50% of its activity by decay.  Each radionuclide has a unique half-life.

Half-Value Layer:  The thickness of any specified material used as shielding necessary to reduce the intensity of an x-ray or gamma ray beam to one-half (1/2) its original value.

High Radiation Area:  An area accessible to individuals in which radiation levels could result in an individual receiving a dose equivalent in excess of 0.1 rem (1mSv) in 1 hour at 30 cm from the radiation sources or from any surface that the radiation penetrates.

Hot Spot:  The region in a radiation/contamination area in which the level of radiation/contamination is noticeably greater than in neighboring regions in the area.

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 the radiation exposure is 100 R/hr at 1 inch from a source, the exposure will be 0.01 R/hr at 100 inches.

Ion:  An atom that has too many or too few electrons resulting in a positive or negative charge, causing it to be chemically active; a free electron or other charged subatomic particle.

Ionizing Radiation:  Alpha particles, beta particles, gamma rays, x-rays, neutrons, high speed electrons, high speed protons, and other particles or electromagnetic radiation capable of producing ions.

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 differing in the mass number.  Almost identical chemical properties exist between isotopes of a particular element.

Lens of the Eye Dose Equivalent (LDE):  A calculated dose to the lens of the eye and is taken as the dose equivalent at a tissue depth of 0.3 cm (300 mg/cm2).

Licensed or Registered Material:  Radioactive material received, possessed, used, transferred or disposed of under a general or specific license or registration issued by KDHE.

Natural Radiation:  Ionizing radiation, not from man-made sources arising from radioactive material.  Natural radiation due to cosmic rays, soil, natural radiation in the human body and other sources of natural radioactivity are always present.  The levels of natural radiation vary with location, weather patterns, and time to some degree.

Nuclide:  A type 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.

Occupational Dose:  The dose received by an individual in the course of employment in which the individual's assigned duties involve exposure to radiation and to radioactive material from licensed and unlicensed sources of radiation, whether in the possession of the licensee or other person. 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.

Photon:  A quantum of energy emitted in the form of electromagnetic radiation.  Gamma rays and x-rays are photons.

Proton:  An elementary nuclear particle with a positive electric charge located in the nucleus of an atom.

Rad:   Unit of absorbed dose.  One rad is equal to one-hundredth of a joule per kilogram of material or the absorption of 100 ergs/gram of material.  One millirad (mrad) equals 0.001 rad.

Radiation Area:  An area accessible to individuals in which there exists radiation at such levels that, at 30 centimeters from the source of the radiation or any surface that the radiations penetrates, an individual could receive a dose equivalent in excess of five millirems in one hour.

Radioisotope:  A nuclide with an unstable ratio of neutrons to protons placing the nucleus in a state of stress. In an attempt to reorganize to a more stable state, it may undergo various types of rearrangement that involve the release of radiation.

Rem:  The special unit of any of the quantities expressed as dose equivalent.  One millirem (mrem) equals 0.001 rem.

Restricted Area:  An area to which access is limited by the licensee for the purpose of protecting individuals against undue risks from exposure to radiation and radioactive materials.

Sealed Source:  Any radioactive material that is permanently encased in a capsule designed to prevent the leakage or escape of the radioactive material.

Shallow Dose Equivalent -Whole Body or Maximum Extremity.(SDE-WB, SDE-ME):  The external exposure of the skin of the whole body or the maximum extremity. It is taken as the dose equivalent at a tissue depth of 0.007 cm (7 mg/cm2) averaged over an area of 1 square centimeter.

Shielding Material:  Any material which is used to absorb radiation and thus effectively reduce the intensity of radiation and in some cases eliminates it.  Examples of commonly used shielding material are lead, concrete, aluminum, water, and plastic.

Stochastic Effects:  Health effects that occur randomly and for which the probability of the effect occurring, rather than its severity, is assumed to be a linear function of dose without threshold.  Hereditary effects and cancer incidence are examples of stochastic effects.

TLD:  Thermoluminescent dosimeter

Unrestricted Area:  An area to which access is neither limited nor controlled by the licensee.

Very High Radiation Area:  An area accessible to individuals in which radiation levels could result in an individual receiving an absorbed dose in excess of 500 rads (5 grays) in one hour at one meter from a source of radiation or from any surface that the radiation penetrates.

Whole Body:  For the purposes of external exposure, head, trunk, arms above the elbow, and legs above the knee.

X-rays:  Penetrating electromagnetic radiation having wave lengths shorter than those of visible light.  They are usually produced by bombarding a metallic target with fast electrons in a high vacuum.  In nuclear reactions, it is customary to refer to photons originating in the nucleus as gamma rays, and those originating in the extra nuclear part of the atom as X-rays.

Z-number:  The number of protons in the nucleus of an atom.

Last modified: May 30, 2014