Tungsten Radiation Shield Glossary C-D

Tungsten Radiation Shield Glossary(C-D)

This page provides a list of general terms that are used to describe aspects of radiation science. Click on the desired term from the list to retrieve the definition for the term.

Chain reaction
A reaction that is self-sustaining. In a fission chain reaction, the nucleus of a fissionable atom absorbs a neutron and fissions (i.e., breaks apart), releasing additional neutrons. These, in turn, can be absorbed by other fissionable nuclei, releasing still more neutrons. A fission chain reaction is self-sustaining when the number of neutrons released in a given time equals or exceeds the number of neutrons lost by absorption in nonfissionable material or by escape from the system.

Charged particle
An ion. An elementary particle carrying a positive or negative electric charge.

Collective dose
The sum of the individual doses received in a given time period by a specified population from exposure to a specified source of radiation.

Committed dose equivalent
The dose to a specific organ or tissue that is received from an intake of radioactive material by an individual over a specified time after the intake. For radiation protection purposes, the specified time is to the age of 70, which is normally taken to be 50 years for a radiation worker and 70 years for a member of the public.

Committed effective dose equivalent
The committed dose equivalent for a given organ multiplied by a weighting factor.

Compact
A group of two or more states formed to dispose of low-level radioactive waste on a regional basis. A number of states have formed compacts.

Contamination
Undesired radioactive material that is deposited on the surface of or inside structures, areas, objects, or people.

Cosmic radiation
Penetrating ionizing radiation, both particulate and electromagnetic, that originates in outer space. Secondary cosmic rays, formed by interactions in the earth's atmosphere, account for about 45 to 50 millirem of the 300 millirem of natural background radiation that an average member of the US public receives in a year.

Counter
A general designation applied to radiation detection instruments or survey meters that detect and measure radiation. The signal that indicates an ionization event has been detected is called a count.

Critical organ
That part of the body that is most susceptible to radiation damage resulting from the specific exposure conditions under consideration, taking into account the dose the various parts of the body receive under the exposure conditions.

Cumulative dose
The total dose resulting from repeated exposures of ionizing radiation to the same portion of the body, or to the whole body, over a period of time.

Curie (Ci)
The original unit used to express the decay rate of a sample of radioactive material. The curie is equal to that quantity of radioactive material in which the number of atoms decaying per second is equal to 37 billion (3.7×1010). It was based on the rate of decay of atoms within one gram of radium. It is named for Marie and Pierre Curie who discovered radium in 1898. The curie is the basic unit of radioactivity used in the system of radiation units in the United States, referred to as "traditional" units.

Decay products
Decay products are also called "daughter products". They are radionuclides that are formed by the radioactive decay of parent radionuclides. In the case of radium-226, for example, nine successive different radioactive decay products are formed in what is called a "decay chain." The chain ends with the formation of lead-206, which is a stable nuclide

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 is also a radiation worker and has voluntarily informed her employer, in writing, of her pregnancy and the estimated date of conception.

Decommission
The process of closing down a facility followed by reducing the residual quantities of radioactive material to a level that permits the release of the property for use.

Decontamination
The reduction or removal of contaminated 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 to permit the quantity of radioactive material decrease as a result of radioactive decay.

Depleted uranium
Uranium having a percentage of uranium-235 smaller than the 0.7 percent found in natural uranium. It is obtained from spent (used) fuel elements or as byproduct tails, or residues, from uranium isotope separation.

Derived air concentration (DAC)
The concentration of radioactive material in air that will result in an annual limit of intake if an individual breathes that air for a year. For a radiation worker, it is assumed air is breathed for 2,000 hours in one year in the workplace.

Detector
A material or device that is sensitive to radiation and can produce a response signal suitable for measurement or analysis. A radiation detection instrument.

Deterministic effect
Health effects, the severity of which varies with the dose and for which a threshold is believed to exist. Deterministic effects generally result from the receipt of a relatively high dose over a short time period. Skin erythema (reddening) and radiation-induced cataract formation is an example of a deterministic effect (formerly called a nonstochastic effect).

Dose
A general term used to refer to the effect on a material that is exposed to radiation. It is used to refer either to the amount of energy absorbed by a material exposed to radiation (see Dose, absorbed) or to the potential biological effect in tissue exposed to radiation (see Dose, equivalent).

Dose rate
The radiation dose delivered per unit time.
Dose, absorbed
The amount of energy deposited in any substance by ionizing radiation per unit mass of the substance. It is expressed numerically in rads (traditional units) or grays (SI units).

Dose, equivalent
The product of absorbed dose in tissue multiplied by a quality factor, and then sometimes multiplied by other necessary modifying factors, to account for the potential for a biological effect resulting from the absorbed dose. (see Quality factor). It is expressed numerically in rems (traditional units) or sieverts (SI units).

Dosimeter
A small portable instrument (such as a film badge, thermoluminescent or pocket dosimeter) for measuring and recording the total accumulated dose of ionizing radiation.

Dosimetry
The theory and application of the principles and techniques involved in the measurement and recording of ionizing radiation doses.