Radiation Terms

Absorbed Dose. The energy imparted to matter by ionizing radiation per unit mass of irradiated material at the place of interest. The rad is a unit of absorbed dose.  
Absorption. Local deposition of energy.  
Accelerator. A device for imparting energy of motion to charged particles.  
Activity. The time rate of transformation of radioactive nuclei. The curie (Ci) is a unit of activity.  
ALARA. ALARA stands for "as low as reasonably achievable." Taking into account the state of technology, we shall make every reasonable effort to maintain exposures to radiation far below the federal and state dose limits. ALARA is the core of the radiation protection program.  
Alpha particle or ray. The nucleus of a helium atom which is ejected from a radioactive nucleus.  
Anode. The electrode of positive polarity.  
Area Monitoring. See monitoring.  
Attenuation. Decrease in the number of particles in a beam of radiation, or decrease in the exposure rate caused by passage of radiation through matter. The decreases result from absorption and scattering.  
Atomic number. The number of positive charges on the nucleus of an atom, and in a neutral atom the number of orbital electrons.  
Background radiation. Radiation arising from sources other than the one directly under consideration. Radiations are always present due to cosmic rays and natural radioactivity of substances in the earth and building materials.  
Beta particle or ray. Electron, positive or negative, emitted by the nucleus of a radioactive atom.  
Bioassays. The determination of kinds, quantities or concentrations, and in some cases, the locations of radioactive material in the human body, whether by direct measurement (in vivo counting) or by analysis and evaluation of materials excreted from the human body.  
Cathode. The electrode of negative polarity.  
Chromosome. One of the threadlike assemblies of DNA and protein in the cell nucleus of a given species and containing the major part of the hereditary material (the genes). The chromosomes become tightly coiled during nuclear division and thus become particularly distinct at that stage.  
Contamination (radioactive). Deposition of radioactive material in any place where its presence is undesirable.  
Cosmic rays. High energy ionizing particles or radiations originating beyond the earth's atmosphere.  
Curie (Ci). A unit of activity equal to 3.7 X lO10 radioactive disintegrations per second (Becquerel).  
Discharge tube. An evacuated tube, such as Crookes  tube, in which electrons and ions are accelerated, and in which glow discharges are observed when both voltage and pressure are favorable.  
Dose equivalent. The product of absorbed dose and several modifying factors (e.g., the quality factor) which permits summing the radiations of different kind as a measure of the expected biological effect.  
Dose rate. The dose per unit time. The unit is the rad per unit time; e.g. rad/hr.  
Dry run. A term used to describe a simulated experiment or demonstration without the source or active element in place, but with all other aspects included.  
Erythema. Reddening of the skin.  
Exposure. A measure of x or gamma radiation at a certain place, based on its ability to produce ionization in air. The roentgen (R) is a unit of exposure.  
Film badge. A pack of appropriate photographic film and filters used to determine radiation exposure.  
Fission. The process in which the nucleus of an atom splits into two (rarely three) large fragments of approximately equal mass with a large release of energy and in which neutrons and other radiations are emitted. The fission fragments are radioactive nuclei.  
Fluoroscope. A device used for observation of the internal features of an object by means of the fluorescence produced on a screen by x rays transmitted through the object.  
Gamma rays. Electromagnetic radiation emitted by the atomic nucleus. Gamma rays have high penetrating ability compared with alpha and beta particles.  
Gene. A unit of DNA within the chromosome associated with the transmission and development of hereditary characteristics of an organism.  
Genetic damage. Alteration of the structure of a gene, or of a chromosome.  
Geiger-Muller counter. A gas filled tube in which gas amplification gives an easily detectable electrical pulse when ionizing radiation enters the tube.  
Gonad. An ovary or testis.  
Half-life. The time in which half the atom of a particular radioactive substance disintegrate to another nuclear form. Also called radioactive or physical half-life. 
Half-life (biological). The time required for the body to eliminate half of the material taken in by natural biological means. 
Half-life (effective). The time required for a radionuclide contained in a biological system, such as a human or an animal, to reduce its activity by half as a combined result of radioactive decay and biological elimination. 
Half-value layer (HVL). Thickness of an attenuator of radiation required to reduce the exposure rate by one half.  
Health Physicist. A person professionally engaged in radiation protection.   
Ion. An atom or group of atoms which is electrically charged because of the loss or gain of electrons.  
Ionizing radiation. Radiation, particulate or electromagnetic, capable of ionizing neutral atoms or molecules.  
Irradiation. Process of exposure to radiation.  
Isotope. One of several nuclides having the same nuclear charge, but different nuclear mass numbers.  
keV (kiloelectron volt). Unit of energy; the energy acquired by an electron falling through a potential difference of 1000 volts.  
Klystron. A high power electron tube for use at microwave frequencies as an amplifier and oscillator.  
kV (kilovolt). A unit of potential difference equal to 1000 volts.    
Labeling Requirement. Work areas which contains radioactive material must be labeled with the "Caution Radioactive Materials" sign. All radioactive wastes must be similarly labeled.  
Magnetron. A high power electron tube used as an oscillator at microwave frequencies.  
Maximum permissible dose. The maximum dose equivalent that the body of a person, or specific parts thereof, shall be allowed to receive in a stated period of time.  
MeV. Million electron volts.  
Micro. The prefix indicating one millionth part of.  
Milli. The prefix indicating one thousandth part of.  
Monitoring. Periodic or continuous determination of exposure rate or dose rate in an area (area monitoring), or of the exposure received by a person (personnel monitoring), or the measurement of contamination levels.  
Mutation. A change in the germ plasm of an individual; this change may be transmitted to subsequent generations.  
Neutron. An uncharged particle having a mass very close to that of a hydrogen atom, which is usually stable when within the nucleus, but is unstable otherwise.  
Nuclide. A particular nuclear species characterized by a specific atomic number and mass number.  
Personnel monitoring. See monitoring.  
Pregnant Radiation Workers. If a radiation worker is pregnant, she may notify the Radiation Safety Officer and declare pregnancy in writing in order for prenatal exposure limits (500 mrem per year) to take effect. She should complete the Declaration of Pregnancy.  
Quality factor. A factor which relates biological effects of different types of radiation. (For X, gamma and beta rays the quality factors are one; for fast neutron, alpha particles and protons up to 10 MeV, the quality factor are ten.)  
Rad. The unit of absorbed dose; one rad is 100 ergs absorbed per gram of any absorber, and is equal to 10-2 Gray.  
Radiation. Energy propagated through space. For the purposes of radiation protection the term is limited to the following kinds of radiation: (1) Electromagnetic radiation (x rays, gamma rays) and (2) corpuscular emission from radioactive substances or other sources (alpha, beta particles and neutrons).  
Radiation protection survey. Evaluation of the radiation hazards around a radiation source. It customarily includes a physical survey of the arrangement and use of the equipment and measurements of the exposure rates under expected operating conditions.  
Radiation safety officer. Person directly responsible for radiation protection. It is his or her duty to ensure that all procedures are carried out in compliance with federal, state and local established regulations and rules.  
Radionuclide. A radioactive nuclide.  
Rectifier. A device which converts alternating current into unidirectional current.   
Rem. A unit of dose equivalent. One rem is equal to 10-2 Sievert.  
Roentgen (R). A unit of exposure of x or gamma radiation based on the ionization that these radiations produce in air. An exposure of one roentgen results in 2.584 X 1O-4 coulomb per kilogram of air.  
Scattered radiation. Radiation that, during passage through matter, has been deviated in direction and may have had its energy diminished.  
Sealed Source. Any byproduct material that is encased in a capsule designed to prevent leakage or escape of the byproduct material. 
Shielding. Barrier of attenuating material used to reduce radiation exposure.   
Source. Radiation producing equipment or an aggregate of radioactive nuclei.   
Tenth-value layer (TVL). The thickness of an absorber required to reduce the exposure rate to one-tenth.  
X rays. Electromagnetic radiation of relatively high energy. In the x-ray tube they are produced by bombarding a metal target with high speed electrons. They are also produced from a rearrangement of the orbital electrons in an atom, due to various causes.  



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 Environmental Health& Safety: MSC-3578, P.O. Box 30001, Academic Research Bldg. C, Rm. 109
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    This page was last updated on 08/22/2008