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RADIATION SAFETY TRAINING MANUAL

CHAPTER 11
GLOSSARY

A Symbol for mass number.

Absorbed dose The amount of energy imparted to matter by ionizing radiation per unit mass of irradiated material at the place of interest (see rad or Gray).

Absorption The process by which radiation imparts some or all of its energy to material through which it passes.

Absorption Coefficient The fractional decrease in the intensity of a beam of x-rays or gamma radiation.

• Linear absorption coefficient (per unit lengths)
• Mass absorption coefficient (per mass thickness)
• Atomic absorption coefficient (per atom)

ALARA ALARA refers to the policy of maintaining radiation levels of exposure As Low As is Reasonably Achievable.

Allowable Limit On Intake (ALI) The annual intake that would lead to an effective committed dose equivalent (a 50 year dose commitment) not exceeding 5 rem and an annual dose equivalent to any single organ or tissue not exceeding 50 rem.

Alpha-Particles These are equivalent in mass (~4 atomic mass units (amu)) and charge (2 positive units) to helium nuclei. They are emitted primarily during decay of heavy nuclides including uranium, thorium, radium and elements in the trans- uranium series. Alpha-particles are emitted with discrete energies characteristic of the radionuclide. The energies for alpha- particles emitted from typical nuclides are in the 3-6 MeV range. Alpha-particles, because of their large mass, have a relatively low velocity. This velocity and the double positive charge mean that alpha-particles interact strongly with matter, producing intense ionization as they dissipate their kinetic energy in very short distances. Alpha-particles with an energy of 5 MeV will penetrate about 50 microns in tissue and produce (20-60)x10³ ion pairs per centimeter in air. In general, alpha-particles can travel only short distances (about 8 cm) in air and can be stopped by a thin sheet of paper, although the highest energy alpha-particles can penetrate to the living basal epidermal cells. When nuclides which emit alpha-particles become deposited within a person's body, those cells within a fraction of a millimeter of the site of deposition will receive very large doses of radiation.

Anode Positive electrode; electrode to which negative ions (or electrons) are attracted.

Area Monitoring Routine monitoring of the level of radiation or of radioactive contamination of any particular area, building, room or equipment.

Atomic Mass The mass of a neutral atom of a nuclide is usually expressed in atomic mass units (amu) which is 1/12 the mass of the neutral ¹⁴C atom.

Atomic Number The number of protons in the nucleus of an atom of a nuclide (symbol Z).

Background Ionizing radiation arising from radioactive material other than the one directly under consideration. Background radiation due to cosmic rays and natural radioactivity is always present. There may also be background radiation due to the presence of radioactive substances in other parts of the building, in the building material itself, etc.

Becquerel (Bq) Special name for the unit of activity of radionuclide. One Bq equals one disintegration per second.

Beta Particles These are emitted from the nucleus and are identical to orbital electrons in mass (1/1840 amu) and charge (1 negative unit). As the result of the emission of a beta-particle (negative), a neutron is converted to a proton in the nucleus so that the atomic number is increased by one. The atomic mass number remains the same. Beta-particles are more penetrating than alpha-particles. A beta-particle will produce 50-200 ion pairs per centimeter of track length in air. Beta-particles are emitted in a spectrum of energies; the average energy is 1/3 of the maximum.

Bioassay Determination of personnel contamination by urine analysis, blood analysis, thyroid analysis or other means.

Bremsstrahlung Electromagnetic radiation produced when charged particles decelerate in matter. The production of bremsstrahlung depends directly upon the energy of the particle and the atomic number of the absorber. This means that large activity, high energy beta sources require shielding with sufficient thickness of low atomic number substances such as plastic. At low energies the fraction of energy converted to bremsstrahlung approximately equals ZE/1000, where Z is the atomic number of the absorber and E is the average of energy of the beta-particles. Usually associated with energetic beta- emitters, e.g., ³²P.

Broad License Normally, the State of California Department of Health Services issues a specific license for each proposed radiation use. In exceptional cases, a Type A Broad Scope Radioactive Material License is issued to an organization for the use of different quantities and types of radioactive materials in research, development or human use. The University of California, San Francisco (UCSF) has a Broad License.

Carrier Free An adjective applied to one or more radionuclides in minute quantity, essentially undiluted with stable radionuclide carrier.

Contamination, Radioactive Deposition of radioactive material in any location where it is not desired, particularly where its presence may be harmful.

Controlled Area A defined area in which occupational exposure of personnel to radiation or radioactive materials is under the supervision of a Radiation Safety Officer. This implies that a controlled area requires control of access, occupancy and working conditions for radiation safety purposes.

Curie (Ci) A unit of radioactivity defined as the quantity of any radionuclide that will produce 3.7x10¹⁰ disintegrations per second. This unit has been replaced in the literature with the term becquerel.

Critical Organ That organ or tissue the irradiation of which will result in the greatest hazard to the health of the individual.

Decay, Radioactive Disintegration of an unstable nuclide by the spontaneous emission of charged particles and/or photons.

Dose A general term denoting the quantity of radiation or energy absorbed in a specified mass. For special purposes it must be appropriately qualified, e.g., absorbed dose.

Dose Equivalent (DE) A quantity used in radiation protection. It expresses all radiations on a common scale for calculating the effective absorbed dose. It is defined as the product of absorbed dose (in rads or grays) and certain modifying factors. The unit is the rem or sievert.

Electron Volt (eV) The unit of energy equivalent to energy gained by an electron passing through a potential difference of 1 volt (a very small unit of energy) 1 eV = 1.6x10-¹² ergs. Usually multiples are used KeV = l000 eV and MeV = 1,000,000 eV.

Film Badges A packet of photographic film used for the approximate measurement of radiation exposure for personnel monitoring purposes. The badge holder may contain two or more films of differing sensitivity, and it may contain filters which shield parts of the film from certain types of radiation.

Gamma-Rays and X-Rays These are part of the electromagnetic energy spectrum which also includes radio waves, visible light and ultraviolet light, etc. X-rays and gamma-rays have very high energies; they have short wavelengths and readily penetrate matter. Gamma-rays and x-rays differ only in their source. Gamma-rays arise from the atomic nucleus while x-rays arise from orbital electron energy transitions.

Both of these radiations interact with matter mainly by transferring energy to orbital electrons of absorber atoms causing ionization. The ejected orbital electrons then decelerate and lose energy, in the same manner as beta-particles. Because the photons have no mass or electrical charge the probabilities of interaction are small and the radiations are difficult to attenuate. Dense materials with high atomic numbers, i.e., lead, uranium, etc., make the best shields against these radiations.

Geiger Mueller (GM) Counter A highly sensitive gas-filled detector and associated circuitry used for radiation detection and measurements.

Gray (Gy) The unit of absorbed dose, namely, absorption of 1 joule in a kilogram of absorbing medium. One gray equals 100 rads (see rad).

Half-life, Biological The time required for a body to eliminate one-half of an administered dose of any substance by the regular process of elimination. This time is approximately the same for both stable and radioactive isotopes of a particular element.

Half-life, Effective The time required for a radioactive nuclide in a system to be diminished 50% as a result of the combined action of radioactive decay and biological elimination.

T_eff = T_bio x T_rad / (T_bio + T_rad)

Half-life, Radioactive The time required for a radioactive substance to lose 50% of its activity by decay. Each radionuclide has a unique half-life.

Half-value Layer (HVL) The thickness of a material which if placed in a radiation beam, for example a shield, will reduce the intensity of the beam by half.

Hazard Guide Value These values are computed by the formula HGV = QTU, where Q equals quantity of radionuclides in mCi; T equals relative toxicity factor based on permissible air concentration of radionuclides; U equals use factor.

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 Any area accessible to individuals, in which there exists radiation at such levels that an individual could receive in any one hour a dose to the whole body in excess of 100 mrem.

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 rate is 50 mR/hr at 1 cm from a source, the exposure rate will be 0.5 mR/hr at 10 cm.

Investigation Level (Action level) A limit set by an organization as an internal control, which if exceeded will result in an investigation and an effort to reduce exposure. This limit is generally set as a small fraction of the Maximum Permissible Body Burden (MPBB).

Ionization The process by which a neutral atom or molecules acquires a positive or negative electrical charge.

Ionizing Radiation Any electromagnetic or particulate radiation capable of producing ions directly or indirectly in its passage through matter. In general, it will refer to gamma-rays and x-rays, alpha and beta-particles, neutrons, protons, high speed electrons and other nuclear particles.

Isotopes Nuclides having the same number of protons in their nuclei, (the same atomic number), but differing in the number of neutrons and therefore in the mass number. Essentially identical chemical properties exist between isotopes of a particular element but they can have different nuclear decay properties.

KeV One-thousand electron volts. This is a unit used to specify the energy of ionizing radiation.

Mass Number The number of nucleons (protons and neutrons) in the nucleus of an atom (Symbol A).

Maximum Permissible Dose (MPD) The maximum dose of radiation which may be received by an individual working with ionizing radiation.

Maximum Permissible Body Burden (MPBB) The quantity of a radionuclide which can be in the body without exceeding the maximum permissible dose equivalent.

MeV One million electron volts. This is a unit used to specify the energy of ionizing radiation.

Monitoring Checking for presence of sources of radiation under a specific set of conditions. Monitoring includes measurements of levels of radiation or concentrations of radioactivity and is done for protection of health.

Neutrons Electrically neutral particles with a mass of about 1 amu. Neutrons can interact with nuclei and transmute stable nuclides into radioactive nuclides. Special precautions may be required around sources where neutrons are being produced to protect against the induced radioactivity in the shielding, air, etc.

Personnel Monitoring Monitoring any part of an individual, his/her breath, excretions or any part of his/her clothing.

Personnel Dosimetry Determination of the cumulative dose of radiation to an individual by various means such as film badges, finger rings, and bioassays.

Positrons These are positively charged beta-particles (equivalent in mass to electrons). They are emitted from the nucleus in the same manner as negatively charged electrons. The process results in a proton being transformed to a neutron. The resulting nucleus will have one less positive charge and the same mass number as the original nucleus. Positrons are emitted in a spectrum of energies. When the positron collides with a negative electron, both particles are annihilated. The masses of the positron and electron (each of which has a mass 1/1840 of an atomic mass unit) are totally converted to energy in accordance with formula E = mc²; two photons with energies of 0.511 MeV are produced. Since the annihilation radiations have the same characteristics as gamma-rays, positron sources require shielding like that for gamma sources.

Quality Factor (QF) Number by which absorbed doses are to be multiplied to obtain dose for radiation protection purposes. It is a quantity that expresses on a common scale the radiation harm incurred by exposed persons. It is selected based upon review of human and animal exposure data for various kinds of radiation. Quantitatively, QF is related only to linear energy transfer of the radiation. The QF for x-rays, gamma-rays and beta-particles is approximately one.

Rad (Radiation Absorbed Dose) The unit of absorbed dose. A dose of one rad means the absorption of l00 ergs of radiation energy per gram of absorber or 0.01 joule per kilogram of absorbing material. This term has been superseded in the literature by the term Gray. 100 rad equal one Gray.

Radioactive Materials Any material, solid, liquid, or gas, which emits ionizing radiation spontaneously.

Radiological Survey An evaluation of the radiation hazards incident to the production, use or existence of radioactive materials or other sources of radiation under a specific set of conditions. Such evaluation customarily includes a physical survey of the disposition of materials and equipment, measurements or estimates of the levels of radiation that may be involved, and a sufficient knowledge of processes using or affecting these materials to predict hazards resulting from expected or possible changes in materials or equipment.

Radiotoxicity A term referring to the potential of a radionuclide to cause damage to living tissue by absorption of energy from the disintegration of the radioactive material introduced into the body.

Relative Biological Effectiveness (RBE) The factor used to compare the biological effectiveness of absorbed radiation doses due to different types of ionizing radiation. This factor is usually 1 for commonly used x-ray, gamma and beta sources.

Rem (Roentgen Equivalent Man) The unit of dose equivalent. The dose equivalent in rems is numerically equal to the absorbed dose in rads multiplied by the quality factor, the distribution factor and other necessary modifying factors. This term has been superseded in the literature by the term sievert. 100 rem equal one sievert.

Restricted Area For purposes of responsibility for radiation safety and for controlling exposure to ionizing radiation, areas under the control of the University of California where radioactive radionuclides are used or stored or ionizing radiation generators are in use are considered restricted areas. Same as Controlled Area.

Roentgen (R) A unit of exposure that is only defined for x-rays and gamma-rays up to the energy of 3 MeV. It is the amount of energy required to produce ions able to carry one electrostatic unit of charge of either sign in 1 cc of dry air at STP. (Survey meter readings of pure beta-emitters must be monitored on the count rate scale not the mR/hr scale.)

Scintillation Counter A counter in which light flashes produced in a scintillator by ionizing radiation are converted into electric pulses by a photomultiplier tube. This may be obtained by the use of a liquid fluor and sample or within or against a solid crystal.

Sealed Source A radioactive source that is hermetically sealed and not intended to be opened.

Sievert (Sv) Special name for the SI unit of dose equivalence. One sievert equals 100 rem.

Specific Activity Total radioactivity of a given nuclide per gram of a compound, element or radioactive nuclide.

Tenth Value Layer (TVL) The thickness of a substance which if introduced into a beam of radiation (for example, as a shield) will reduce the intensity of the beam by a factor 10.

Tracer, Isotopic The radionuclide or non-natural mixture of radionuclides of an element which may be incorporated into a sample to make possible observation of the course of that element, alone or in combination, through a chemical, biological, or physical process. The observations may be made by measurement of radioactivity or of isotopic abundance.

User Any person who is involved with handling radionuclides. This definition includes students, staff, visiting appointees and faculty. All users must have an approved user training number, a Supplement A (training and experience record) on file and be personally instructed by the license-holder or an alternate in practical safety matters.

Wipe Test A procedure in which a swab, e.g., a circle of filter paper, is rubbed on a surface, generally over an area of approximately 100 cm², and its radioactivity measured to determine if the surface is contaminated with loose radioactive material.

X-Rays Part of the electromagnetic energy spectrum which also includes radio waves, infrared, visible light and ultraviolet light, etc. x-rays and Gamma-rays have very high energies; they have short wave lengths and readily penetrate matter. Gamma-rays and x-rays differ only in their source. Gamma-rays arise from the atomic nucleus while x-rays arise from orbital electron energy transitions. x-rays produced by machines usually have two components: bremsstrahlung and characteristic x- rays.

Both of these radiations interact with matter mainly by transferring energy to orbital electrons of absorber atoms causing ionization. The ejected orbital electrons then decelerate and lose energy, in the same manner as beta-particles. Because the photons have no mass or electrical charge, the probabilities of interaction are small and the radiations are difficult to attenuate. Dense materials with high atomic numbers, i.e., lead, uranium, etc., make the best shields against these radiations.

Z Symbol for atomic number.

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