AC 20-48 Page 21 1966 Appendix II. GLOSSARY Alpha Particle-A particle emitted spontaneously from the nuclei of some radioactive elements.
It is identical with a helium nucleus, having a mass of four units and an electric charge of two positive units. It travels only a few inches, even in air, but can be very harmful if ingested by breathing or taken into the blood stream through an open wound.
Attenuation--The absorption or stopping of some of the radiation as it passes into or through solid materials.
Beta Particle-A charged particle of very small mass emitted spontaneously from the nuclei of certain radioactive elements. Most, if not all, of the direct fission products emit (negative) beta particles. Physically, the beta particle is identical with an electron moving at high velocity. The beta particle is the cause of beta burns to the skin, which may be very serious.
Buffer Zone-An area that has been decontaminated immediately beyond and in addition to the intended working area.
Clean Area-One in which decontaminating measures have been taken to reduce the amount of residual radioactivity.
Contamination-Deposit of radioactive material on the surface of structures, areas, objects, or personnel following a nuclear (or atomic) explosion. This material generally consists of fallout in which fission products and other weapon debris become incorporated with particles of dirt, etc.
Contamination can also arise from the radioactivity induced in certain substances by the action of neutrons from a nuclear explosion.
Cross-contamination--The contamination of a previously "clean" area by radioactive material which is windblown, or tracked on shoes or vehicle tires, etc.
Decoy-Sometimes referred to as natural decay is the decrease of any radioactive material with the passage of time.
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 so as to remove or decrease the contamination;
(2) letting the material stand so that the radioactivity is decreased as a result of natural decay ;
(3) covering the contamination to attenuate the radiation emitted.
Radioactive material removed must be disposed of by burial on land or at sea, or by other suitable methods.
Dosage (dose)A total or accumulated quantity of ionizing (or nuclear) radiation. A dosage can be measured by reading a pocket dosimeter or it can be calculated by multiplying the hours of exposure times the rate of radiation, which is expressed in terms of roentgens or milliroentgens per hour.
Dose Rate-As a general rule, the amount of ionizing (or nuclear) radiation to which an individual would be exposed or which he would receive per unit of time. It is usually expressed as roentgens or milliroentgens per hour. The dose rate is commonly used to indicate the level of radioactivity in a contaminated area.
Dosimeter--An instrument for measuring and registering total accumulated exposure to ionizing radiation (pronounced - dosimeter).
Gamma Rays (or Radiations)-Electromagnetic radiations of high energy originating in atomic nuclei and accompanying many nuclear reactions, e.g., fission, radioactivity, and neutron capture. Physically, gamma rays are identical
with x-rays of high energy, the only essential difference being that the X-rays do not originate from the atomic nuclei, but are produced in other ways. Gamma rays probably constitute the greatest threat in radioactivity and are the main reason for decontaminating-to remove the source of this type of radiation.
Milliroentgen (mr)-A one-thousandth part of a roentgen.
Monitoring-Procedure of locating and measuring radioactive contamination by means of survey instruments which can detect and measure (as dose rates) ionizing radiations. (The individual performing the operation is known as a monitor.)
Radiation Levels-Measure of ionizing radiation at specified periods, usually read from survey meters as-mr/hr. or r/hr.
Radioactivity-The spontaneous emission of radiation, generally alpha or beta particles, often accompanied by gamma rays, from the nuclei of an unstable isotope. As a result of this emission, the radioactive isotope is converted (or decays) into the isotope of a different (daughter) element which may or may not also be radioactive. Ultimately, as a result of one or AC 20-48 1966 more stages of radioactive decay, a stable nonradioactive end product is formed.
Roentgen-A unit of exposure dose of gamma (or X-) radiation. Survey meters and dosimeters show readings either in roentgen units or milliroentgen units.
Stay Time-The period of time personnel can work or stay in an area at the existing dose rate of radiation without exceeding the prescribed maximum dose.
Shielding-Any material or obstruction which absorbs (attenuates) radiation and thus tends to protect personnel or materials from the effects of a nuclear (or atomic) explosion. A moderately thick layer of any opaque material will provide satisfactory shielding from heat radiation, but a considerable thickness of material of high density may be needed for nuclear radiation shielding.
Survey Meter-A portable instrument, such as a Geiger Counter or ionizing chamber, used to detect and measure nuclear radiation. These measurements are in terms of the rate of radiation, either roentgens per hour or milliroentgens per hour.
* U.S. Government Printing Office: 1991 - 517-000/46019