61 Radioactive Materials Safety Manual Half-Life, Effective – time required for a radioactive nuclide in a system to be diminished by 50% 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 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 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. High Radiation Area – an area, accessible to individuals, in which radiation levels could result in an individual receiving a dose equivalent in excess of 100 mrem (1 mSv) in one hour at thirty centimeters from the radiation source 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. Individual Monitoring Devices – devices designed to be worn by a single individual for the as-sessment of dose equivalent such as film badges, thermoluminescent dosimeters (TLDs), pocket ionization chambers, and personal air sampling devices. 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, causing it to be chemically active; such as an electron that is not associated (in orbit) with a nucleus. Ions may be positively or negatively charged, and vary in size. Ionization is the process by which a neutral atom or molecule acquires either a positive or a negative charge. An ionization chamber is 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. 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 in the mass number. Almost identical chemical properties exist between radionuclides of a particular element. Joule – the meter-kilogram-second unit of work or energy, equal to the work done by a force of one Newton when its point of application moves through a distance of one meter in the direction of the force. Labeled Compound – a compound consisting, in part, of labeled molecules. By observations of radioactivity or isotopic composition this compound or its fragments may be followed through physical, chemical or biological processes. Late Health Effects – are effects the exhibit themselves a period of years after an exposure. The incidence is generally dependent on the radiation dose, dose rate, age at the time of the exposure Licensed Material – source material, special nuclear material, or by-product material received, possessed, used, transferred or disposed of under a general or specific license issued by the Nuclear Regulatory Commission or an Agreement State. Licensee – the holder of the license. Limits – the permissible upper bounds of radiation exposures, contamination or releases.. Luxel® Dosimeter – a dosimetry badge introduced by Landauer, Inc. that uses optically stimulated luminescence of a special aluminum oxide phosphor. A laser light source is used to stimulate luminescence
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