Radioactive Materials Branch
General Definitions used in Health Physics & Radiation Protection

D

Daughter Products
Isotopes that are formed by the radioactive decay of some other isotope. In the case of radium-226, for example, there are 10 successive daughter products, ending in the stable isotope lead-206.

Decay, Radioactive
The decrease in the amount of any radioactive material with the passage of time, due to the 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 the licensee, in writing, of her pregnancy and the estimated date of conception.  The declaration remains in effect until the declared pregnant woman withdraws the declaration in writing or is no longer pregnant.

Decontamination
The reduction or removal of contaminating radioactive material from a structure, area, object, or person. Decontamination may be accomplished by:

Decommission
To remove (as a facility) safely from service and reduce residual radioactivity to a level that permits release of the property for unrestricted use and termination of the license.

Deep-dose equivalent (H_d)
As it applies to external whole-body exposure, is the dose equivalent at a tissue depth of one cm (1000 mg/cm²).

Demand Respirator
An atmosphere-supplying respirator that admits breathing air to the facepiece only when a negative pressure is created inside the facepiece by inhalation.

Department
The North Carolina Department of Environment and Natural Resources.

Depleted uranium
The source material uranium in which the isotope uranium-235 is less than 0.711 weight percent of the total uranium present. Depleted uranium does not include special nuclear material.

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 ALI. DAC values are given in Table 1, Column 3, of Appendix B to 10 CFR §§ 20.1001 - 20.2041).

Derived air concentration-hour (DAC-hour)
The product of the concentration of radioactive material in air (expressed as a fraction or multiple of the derived air concentration for each radionuclide) and the time of exposure to that radionuclide, in hours. A licensee may take 2,000 DAC-hours to represent one ALI, equivalent to a committed effective dose equivalent (CEDE) of five rems (0.05 Sv).

Diagnostic clinical procedures manual
A collection of written procedures governing the use of radioactive material that describes each method by which the licensee performs diagnostic clinical procedures and includes other instructions and precautions. Each diagnostic clinical procedure including but not limited in content to the radiopharmaceutical, dosage and route of administration, shall be approved by an authorized user prior to inclusion in the manual. The radiation safety officer shall ensure that the manual includes the approved written procedure for all diagnostic clinical procedures performed at the facility.

Disposable Respirator
An respirator for which maintenance is not intended and that is designed to be discarded after excessive breathing resistance, sorbent exhaustion, physical damage, or end-of-service life renders it unsuitable for use.  Examples of this type of respirator are a disposable half-mask respirator or a disposable escape-only self-contained breathing apparatus (SCBA).

Distinguishable from Background
Means that the detectable concentration of a radionuclide is statistically different from the background concentration of that radionuclide in the vicinity of the site or, in the case of structures, in similar materials using measurement technology, survey and statistical techniques as defined in 10 CFR 20.1003.

DOE
(United States) Department of Energy

Dose (or radiation dose)
A generic term that means absorbed dose, dose equivalent, effective dose equivalent, committed dose equivalent, effective dose equivalent, or total effective dose equivalent, as defined in other areas in the North Carolina Regulations for Protection Against Radiation.

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).

Dose limits
(see "Limits" defined below).

Dosimeter
A portable instrument for measuring and registering the total accumulated dose to ionizing radiation

Dosimetry processor
An individual or an organization that processes and evaluates individual monitoring equipment in order to determine the radiation dose delivered to the equipment.

E

Effective dose equivalent (H_E)
The sum of the products of the dose equivalent to the organ or tissue (H_T) and the weighting factors (w_T) applicable to each of the body organs or tissues that are irradiated (H_E = w_TH_T).

Effective Half-life
The time required for the amount of a radioactive element deposited in a living organism to be diminished 50% as a result of the combined action of radioactive decay and biological elimination.

Electromagnetic Radiation
A traveling wave motion resulting from changing electric or magnetic fields. Familiar electromagnetic radiation range from X-rays (and gamma rays) of short wavelength, through the ultraviolet, visible, and infrared regions, to radar and radio waves of relatively long wavelength. All electromagnetic radiations travel in a vacuum with the velocity of light.

Electron
An elementary particle with a negative charge and a mass 1/1837 that of the proton. Electrons surround the positively charged nucleus and determine the chemical properties of the atom.

Embryo/fetus
The developing human organism from conception until the time of birth.

Energy compensation sources (ECS) <as used in 15A NCAC 11 .1300>
A sealed source, with an activity not exceeding 100 microcuries (3.7 MBq), used within a logging tool or other tool components, to provide a reference standard to maintain the tool's calibration when in use.

Entrance (or access) point
Any location through which an individual could gain access to radiation areas or to a source of radiation. This includes entry or exit portals of sufficient size to permit human entry, irrespective of their intended use.

Equipment services
The selling, installation, rebuilding, conversion, repair, inspection, testing, survey or calibration of equipment which can affect compliance with 15A NCAC 11 by a licensee or registrant.

Erg
Is the unit of work done by a force of one (1) dyne acting through a distance of one (1) centimeter.  The unit of the erg is expressed as 1 gm-cm²/sec².   There are 1 x 10⁷ ergs per Joule.

Exposure
Being exposed to ionizing radiation or to radioactive material.

Exposure head
A device that locates the gamma radiography sealed source in the selected working position.  Commonly called a source stop.

Exposure rate
The exposure per unit of time, such as R/min and mR/h.

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

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

Eye Dose Equivalent
See "Lens Dose Equivalent" below.

F

FDA
(United States) Food and Drug Administration

FEMA
Federal Emergency Management Administration

Film Badge
A pack of photographic film used for measurement of radiation exposure for personnel monitoring purposes. The badge may contain two or three films of differing sensitivities, and it may contain a filter that shields part of the film from certain types of radiation.

Field examination
A demonstration of practical application of principles learned in the classroom that shall include use of all appropriate equipment and procedures.

Filtering facepiece (dust mask)
A negative pressure particulate respirator with a filter as an integral part of the facepiece or with the entire facepiece composed of the filtering medium, not equipped with elastomeric sealing surfaces and adjustable straps.

Fit factor
A quantitative estimate of the fit of a particular respirator to a specific individual, and typically estimates the ratio of the concentration of a substance in ambient air to its concentration inside the respirator when worn.

Fit test
The use of a protocol to qualitatively or quantitatively evaluate the fit of a respirator on an individual.

G

Gamma Ray
High-energy, short wavelength, electromagnetic radiation (a packet of energy) emitted from the nucleus. Gamma radiation frequently accompanies alpha and beta emissions and always accompanies fission. Gamma rays are very penetrating and are best stopped or shielded by dense materials, such as lead or uranium. Gamma rays are similar to X-rays.

Generally applicable environmental radiation standards
Standards issued by the U.S. Environmental Protection Agency (EPA) under the authority of the Atomic Energy Act of 1954 (42 U.S.C. 2D11 et seq.;), as amended, that impose limits on radiation exposures or levels, or concentrations or quantities of radioactive material, in the general environment outside the boundaries of locations under the control of persons possessing or using sources of radiation.

Geiger-Mueller Counter
A 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 the radiation field. It was named for Hans Geiger and W. Mueller, who invented it in the 1920's. It is sometimes called simply a Geiger counter or a G-M counter.

Giga-
A prefix that multiplies a basic unit by 1,000,000,000 (one billion).

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