Glossary


absorbed dose:

The energy imparted by ionizing radiation per unit mass of material irradiated. For purposes of radiation protection and assessing risks to human health, the quantity normally calculated is the average absorbed dose in an organ or tissue, given by the total energy imparted to that organ or tissue divided by the total mass. The SI unit of absorbed dose is the joule per kilogram (J kg−1), and its special name is the gray (Gy). In conventional units used in this report, absorbed dose is given in rads; 1 rad = 0.01 Gy.

absorption:

The passage of a substance across an exchange barrier in the respiratory tract, gastrointestinal tract, or skin into blood.

accuracy:

The extent of agreement between a measurement or prediction of a quantity and its actual value. An accurate measurement or prediction should be precise and unbiased. See also bias and precision.

activation:

The production of radionuclides by capture of radiation (for example, neutrons) in atomic nuclei.

activity:

The rate of transformation (or distintegration or decay) of radioactive material. The SI unit of activity is the reciprocal second (s−1), and its special name is the becquerel (Bq). In conventional units used in this report, activity is given in curies (Ci); 1 Ci = 3.7 × 1010 Bq.

activity median aerodynamic diameter:

The diameter in an aerodynamic particle-size distribution for which the total activities on particles above and below this size are equal. A lognormal distribution of particles sizes usually is assumed.

agent:

An active force (such as ionizing radiation) or substance that produces or is capable of producing an effect.



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Glossary absorbed dose: The energy imparted by ionizing radiation per unit mass of material irradiated. For purposes of radiation protection and assessing risks to human health, the quantity normally calculated is the average absorbed dose in an organ or tissue, given by the total energy imparted to that organ or tissue divided by the total mass. The SI unit of absorbed dose is the joule per kilogram (J kg−1), and its special name is the gray (Gy). In conventional units used in this report, absorbed dose is given in rads; 1 rad = 0.01 Gy. absorption: The passage of a substance across an exchange barrier in the respiratory tract, gastrointestinal tract, or skin into blood. accuracy: The extent of agreement between a measurement or prediction of a quantity and its actual value. An accurate measurement or prediction should be precise and unbiased. See also bias and precision. activation: The production of radionuclides by capture of radiation (for example, neutrons) in atomic nuclei. activity: The rate of transformation (or distintegration or decay) of radioactive material. The SI unit of activity is the reciprocal second (s−1), and its special name is the becquerel (Bq). In conventional units used in this report, activity is given in curies (Ci); 1 Ci = 3.7 × 1010 Bq. activity median aerodynamic diameter: The diameter in an aerodynamic particle-size distribution for which the total activities on particles above and below this size are equal. A lognormal distribution of particles sizes usually is assumed. agent: An active force (such as ionizing radiation) or substance that produces or is capable of producing an effect.

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alpha particle: An energetic nucleus of a helium atom, consisting of two protons and two neutrons, that is emitted spontaneously from nuclei in decay of some radionuclides; also called alpha radiation and sometimes shortened to alpha (for example, alpha-emitting radionuclide). Alpha particles are weakly penetrating and can be stopped by a sheet of paper or the outer dead layer of skin. atmospheric testing: Detonation of nuclear weapons or devices in the atmosphere or close to the earth’s surface as part of the nuclear-weapons testing program. atom: The smallest particle of a chemical element that cannot be divided or broken up by chemical means. An atom consists of a central nucleus of protons and neutrons and orbital electrons surrounding the nucleus. atomic bomb: A nuclear weapon that relies on fission only, in contrast to a thermonuclear (“hydrogen”) bomb that uses fission and fusion. atomic nucleus: The dense core of an atom, composed of protons and neutrons. atomic veteran: A person who, while serving as a member of the armed forces, was a participant at one or more atmospheric nuclear-weapons tests, served in occupation forces in Hiroshima or Nagasaki, Japan, or was a prisoner of war in Japan at the time of the bombings of Hiroshima and Nagasaki. attenuation: The reduction in intensities of radiation in passing through matter by a combination of scattering and other interactions with electrons and atomic nuclei. background radiation: Ionizing radiation that occurs naturally in the environment including: cosmic radiation; radiation emitted by naturally occurring radionuclides in air, water, soil, and rock; radiation emitted by naturally occurring radionuclides in tissues of humans and other organisms; and radiation emitted by human-made materials containing incidental amounts of naturally occurring radionuclides (such as building materials). Background radiation may also include radiation emitted by residual fallout from nuclear-weapons tests that has been dispersed throughout the world. The average annual effective dose due to natural background radiation in the United States is about 0.1 rem, excluding the dose due to indoor radon, and the average annual effective dose due to indoor radon is about 0.2 rem. badged dose: An estimate of a person’s external radiation dose, specifically the deep equivalent dose from external exposure to photons, as derived from readings of exposure by one or more film badges assigned to the person. basal cells: Cells in the epidermis that give rise to more specialized cells and act as stem cells. basal cell carcinoma: A malignant growth originating from basal cells that is most common in fair-skinned or sun-exposed areas; the most common form of skin cancer. becquerel: The special name for the SI unit of activity; 1 Bq = 1 s−1.

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beta-to-gamma dose ratio: An estimated ratio of the equivalent dose to the skin or lens of the eye from external exposure to beta particles to the associated equivalent dose to the whole body from external exposure to photons. beta particle: An energetic electron emitted spontaneously from nuclei in decay of some radionuclides and produced by transmutation of a neutron into a proton; also called beta radiation and sometimes shortened to beta (for example, beta-emitting radionuclide). Beta particles are not highly penetrating, and the highest-energy beta radiation can be stopped by a few centimeters of plastic or aluminum. bias: The systematic tendency of a measurement or prediction of a quantity to overestimate or underestimate the actual value, on average. See also accuracy and precision. bias factor: In external radiation dosimetry, an estimated ratio of the exposure recorded by a film badge to the corresponding deep equivalent dose in humans. The bias factor normally is greater than 1. bioassay: The determination of the kinds, quantities or concentrations, and, in some cases, locations of radioactive material in the human body, either by direct measurement (in vivo counting) or by analysis of materials excreted or removed from the body. biokinetic model: A model describing the time course of absorption, translocation, distribution in organs or tissues, metabolism, and excretion of a substance (such as a radionuclide) introduced into the body by ingestion, inhalation, or absorption through the skin or an open wound. biological effectiveness: The ability of ionizing radiation to induce biological responses in tissues of humans. The biological effectiveness of a particular type of ionizing radiation may be represented by the quality factor, radiation effectiveness factor, radiation weighting factor, or relative biological effectiveness. biological half-time: The time required for half the quantity of a material taken into the body to be eliminated from the body by biological processes. For radionuclides, the biological half-time does not include elimination by radioactive decay. biological response: A significant adverse effect in an organism resulting from exposure to a hazardous agent. The determination of whether an effect is significant or adverse sometimes involves subjective judgment. Often called a biological endpoint or biological effect in the literature. calibration: The check or correction of a measuring instrument by comparing an instrument reading with a standard of known accuracy, in order to ensure acceptable operational characteristics. cancer: A malignant tumor of potentially unlimited growth that expands locally by invasion and systemically by metastasis. carcinogen: An agent capable of inducing cancer.

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carcinoma: A malignant tumor that occurs in epithelial tissues, which cover the body or body parts and serve to enclose and protect those parts, to produce secretions and excretions, and to function in absorption. cataract: A clouding of the lens of the eye, or its capsule, that obstructs the passage of light. central estimate: A “best” estimate of the dose received by an individual, as distinct from an upper bound of the dose that accounts for uncertainty in that estimate. chronic lymphocytic leukemia: A slowly progressing form of leukemia, characterized by an increase in the number of white blood cells known as lymphocytes, which studies have not shown to be caused by radiation in humans. ciliary action: Locomotion produced by the movement of minute hair-like cells on the surface of tissues, especially in the respiratory tract. clearance: The removal of inhaled substances from the respiratory tract by mechanical processes or absorption. Code of Federal Regulations: Codification of general and permanent rules published in the Federal Register by executive departments and agencies of the federal government and published annually by the US Government Printing Office. coefficient of variation: Ratio of the standard deviation of a set of values to the mean. cohort: A group of individuals having a common association or factor. committed dose: The dose (that is, the absorbed dose, equivalent dose, effective dose, or effective dose equivalent) delivered to specified organs or tissues over a specified period after an acute intake of a radionuclide by ingestion, inhalation, or absorption through the skin or an open wound. For adults, the period over which committed doses are calculated normally is 50 years. composite dose coefficient: A dose coefficient that applies to an assumed mixture of radionuclides of specified relative activities. confidence interval: An estimate of the range within which the true value of an uncertain quantity is expected to occur in a specified percentage of measurements or predictions. For example, a 90% confidence interval of (x, y) means that, on the basis of available information, the probability is 0.9 that the true value lies between x and y. See also lower confidence limit and upper confidence limit. correlation: The degree of linear association between two variables, normally described by a unitless correlation coefficient that lies between −1 and +1. A correlation coefficient of 0 implies no linear association, whereas a value of −1 or +1 implies a perfect linear association, one variable increasing while the other decreases in the first instance, and both increasing in the second.

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cosmic radiation: Particulate and electromagnetic radiation that originates in space, including secondary radiation produced by interactions with the constituents of the earth’s atmosphere. curie: The conventional unit of activity, equal to 3.7 × 1010 disintegrations per second (Bq). database: An organized set of data or collection of files that can be used for a specific purpose. deck log: A document that records the daily activities of Navy and Coast Guard ships, including a list of officers on board. deep equivalent dose: The equivalent dose from external exposure of the whole body estimated at a depth of 1 cm in tissue and intended to represent an upper bound of the equivalent dose to the major organs and tissues of the body other than skin and lens of the eye. deposition: (A) The transfer of airborne materials to the ground or other surface. (B) The accumulation of materials in organs or tissues of the body after intake by inhalation, ingestion, or absorption through the skin or an open wound. deposition velocity: Ratio of the flux of a contaminant from the atmosphere to the ground or other surface to the concentration in air above the surface. diffusion: The spreading of a material in a medium due to thermal or mechanical agitation in response to a concentration gradient. dispersion: The spreading of a flowing substance in a medium due to random variations in the structure of the medium or in the speed and direction of flow. dose: A quantification of exposure to ionizing radiation, especially in humans. In this report, the term is used to denote average absorbed dose in an organ or tissue, equivalent dose, effective dose, or effective dose equivalent, and to denote dose received or committed dose. The particular meaning should be clear from the context in which the term is used. dose assessment: Estimation of radiation doses received by specified individuals or populations under specified conditions of exposure. See also dose reconstruction. dose coefficient: (A) For intakes of a specific radionuclide by inhalation, ingestion, or absorption through the skin or an open wound, the committed dose per unit activity intake. (B) For external exposure to a specific radionuclide in air, water, or soil or on the body surface, the dose rate per unit concentration in the specified source region. Usually referred to as a dose conversion factor in earlier literature. dose conversion factor: See dose coefficient. dose equivalent: See equivalent dose. dose rate: Dose received per unit time, often expressed as an average over some period (such as an hour or a day).

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dose reconstruction: The process of estimating doses to individuals or populations at some time in the past from exposure to ionizing radiation (or other hazardous agents) on the basis of assumed exposure scenarios. dose-response analysis: A statistical analysis to estimate values of parameters that describe the relationship between the dose of a hazardous agent (such as ionizing radiation) and an increase in a specified biological response (such as a cancer or other health effect) above the normal (background) incidence. In assessing cancer risks in humans from exposure to ionizing radiation, for example, linear or linear-quadratic dose-response relationships are used most commonly. dosimeter: A portable instrument for measuring and registering the total accumulated exposure to ionizing radiation. dosimetric model: (A) For internal exposure to radionuclides, a model that estimates the dose in specific organs or tissues per disintegration of a specific radionuclide in a specified source organ (site of deposition or transit in the body). (B) For external exposure, a model that estimates the dose rate in specific organs or tissues per unit activity concentration of a specific radionuclide in a specified source region, or the dose rate in specific organs or tissues per unit fluence of radiations at the body surface. dosimetry: The measurement and recording or estimation by calculation of radiation doses or dose rates. effective dose: The sum over specified organs or tissues of the equivalent dose in each tissue modified by the tissue weighting factor, as defined in ICRP (1991a). Supersedes effective dose equivalent. effective dose equivalent: The sum over specified organs or tissues of the average dose equivalent in each tissue modified by the tissue weighting factor, as defined in ICRP (1977). Now superseded by effective dose. effective resuspension factor: A factor used to estimate airborne concentrations of contaminants (assumed to be uniformly distributed with height) that resulted in known concentrations deposited on the ground or other surface, given by the reciprocal of the assumed height of the atmospheric cloud from which deposition occurred. See also resuspension factor. electron: An elementary particle with a unit charge of about 1.602 × 10−19 coulomb and rest mass of 1/1837 that of a proton. Electrons that orbit the nucleus of an atom determine its chemical properties. electron paramagnetic resonance: The process of resonant absorption of radiation by ions or molecules that are mildly attracted to a magnetic field with at least one unpaired electron spin and in the presence of a static magnetic field. electron volt: The kinetic energy attained when a particle of unit electronic charge is accelerated through a difference in electric potential of 1 volt (V). element: A substance that cannot be separated by ordinary chemical methods. Elements are distinguished by the numbers of protons in the nuclei of their atoms.

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epidemiology: The study of the incidence, distribution, and causes of health conditions and events in populations. epidermis: The outer layer of the skin. equivalent dose: A quantity developed for purposes of radiation protection and assessing risks to human health in general terms, defined as the average absorbed dose in an organ or tissue modified by the radiation weighting factor for the type, and sometimes energy, of the radiation causing the dose, as defined in ICRP (1991a). Supersedes average dose equivalent, as defined in ICRP (1977). The SI unit of equivalent dose is the joule per kilogram (J kg−1), and its special name is the sievert (Sv). In conventional units used in this report, equivalent dose is given in rem; 1 rem = 0.01 Sv. error: The difference between an estimated value of a quantity and its actual value. estimate: A measure of or statement about the value of a quantity that is known, believed, or suspected to incorporate some degree of error. exposure: (A) A general term indicating human contact with ionizing radiation, radionuclides, or other hazardous agents. (B) For the purpose of measuring levels of ionizing photon radiation, the absolute value of the total charge of ions of one sign produced per unit mass of air when all electrons and positrons liberated or created by photons in air are completely stopped in air. Exposure is the quantity measured, for example, by a film badge. The SI unit of exposure is the coulomb per kilogram (C kg−1). In conventional units used in this report, exposure is given in roentgens (R); 1 R = 2.58 × 10−4 C kg-1. exposure pathway: The physical course of a radionuclide or other hazardous agent from its source to an exposed person. exposure route: The means of intake of a radionuclide or other hazardous agent by a person (such as ingestion, inhalation, or absorption through the skin or an open wound). exposure scenario: In this report, the set of circumstances in which an individual or group was exposed to ionizing radiation. Characterization of an exposure scenario usually relies on assumptions about the activities of an individual or group, the times and locations of the activities, and the radiation environment in which the activities took place. external dose: The dose to organs or tissues of the body due to sources of ionizing radiation located outside the body, including sources deposited on the body surface. extrapolation: Use of a dataset or model under conditions different from those for which it was established. fallout: Deposition of radioactive particles produced by detonation of a nuclear weapon.

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film badge: Photographic film shielded from light and worn by a person or placed in a specific location to measure and record external exposure to ionizing radiation. fireball: The highly luminous cloud of vaporized fission and activation products, device constituents, and surrounding support material created by a nuclear detonation. fissile: Capable of undergoing fission by interaction with neutrons. Fissile isotopes used in nuclear weapons include uranium-235 and plutonium-239. fission: The splitting of an atomic nucleus into two or more atomic nuclei accompanied by release of neutrons, photons, and energy in the form of kinetic energy of the fission products. In nuclear weapons, fission occurs mainly as a result of capture of neutrons by nuclei of uranium-235 or plutonium-239. fission product: An atomic nucleus, either stable or radioactive, produced in fission or by decay of a radionuclide produced in fission. fission yield: See yield. fluence: The number of radiations incident on a sphere per unit cross-sectional area. flux: The volume of material crossing or impinging on a given cross-sectional area of a surface per unit time divided by the area of the cross section. fractionation: The chemical and physical separation of radionuclides produced in a nuclear detonation caused by differences in condensation rates as the fireball cools. free-in-air exposure: The amount of ionization in air produced by incident photons in the absence of any other medium, such as the human body or a structure that might result in attenuation of the radiation. fusion: The joining together of two atomic nuclei to form heavier nuclei accompanied by release of energy caused by the smaller mass of the heavier nucleus compared with the combined masses of the original nuclei. gamma radiation: Electromagnetic radiation emitted in de-excitation of atomic nuclei, frequently occurring as a result of decay of radionuclides; also called gamma rays and sometimes shortened to gamma (for example, gamma-emitting radionuclide). High-energy gamma radiation is highly penetrating and requires thick shielding, such as up to 1 m of concrete or a few tens of centimeters of steel. See also photon and x radiation. gastrointestinal tract: Organs of the digestive system, including the esophagus, stomach, small intestine, and upper and lower large intestine (colon). Geiger counter: An instrument, consisting of a gas-filled tube containing electrodes between which an electric voltage is maintained, used to detect ionizing radiation. When radiation passes through the tube, short pulses of current are generated, which are measured and related to the intensity of the radiation. generic: Of, applied to, or referring to a whole kind, class, or group. In this report, the term refers to assumptions intended to be broadly applicable to

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a defined group of participants in the atmospheric nuclear-weapons testing program, especially assumptions concerned with the group’s exposure to ionizing radiation. geometric mean: The nth root of the product of n observations or predictions of a quantity. geometric standard deviation: The exponential of the standard deviation of the natural logarithms of a set of values. gray: The special name for the SI unit of absorbed dose; 1 Gy = 1 J kg−1. ground zero: The point on the surface of land or water at or vertically below or above the center of the burst of a nuclear weapon. half-life: The time required for half the atoms of a particular radionuclide to decay to another nuclear state. Hodgkin’s disease: A type of lymphoma that appears to originate in a particular lymph node and to spread to the spleen, liver, and bone marrow and is characterized by progressive enlargement of the lymph nodes, spleen, and general lymph tissue. incidence: The rate of occurrence of new cases of a specific disease, calculated as the number of new cases during a specified period divided by the number of individuals at risk of the disease during that period. internal dose: The dose to organs or tissues of the body due to sources of ionizing radiation in the body. International System of Units (SI): A modern version of the meter-kilogram-second-ampere system of units, which is published and controlled by an international treaty organization (International Bureau of Weights and Measures). ion: An atom or molecule that carries a positive or negative electric charge as a result of having lost or gained one or more electrons. ionizing radiation: Any radiation capable of displacing electrons from atoms or molecules, thereby producing ions. Examples include alpha particles, beta particles, gamma rays or x rays, and cosmic rays. The minimum energy of ionizing radiation is a few electron volts (eV); 1 eV = 1.6 × 10−19 joules (J). isopleth: A line on a map connecting points at which a given variable is assumed to have a specified constant value. isotope: A form of a particular chemical element determined by the number of neutrons in the atomic nucleus. An element may have many stable or unstable (radioactive) isotopes. isotropic: Exhibiting properties with the same values in all spatial directions. kiloton: A measure of explosive force equivalent to that of 1,000 tons of trinitrotoluene (TNT). latent period: The earliest time after exposure to a carcinogenic agent when a cancer caused by that exposure can be manifested; also called latency period. Latin hypercube sampling method: A technique of stratified random sampling from specified probability distributions of variables in which the distribu

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tions are divided into intervals of equal probability and one sample is taken at random from each interval. See also Monte Carlo analysis. leukemia: A group of malignant, commonly fatal blood diseases with common characteristics, including progressive anemia, internal bleeding, exhaustion, and a marked increase in the number of white cells (generally their immature forms) in circulating blood. linear energy transfer: The energy lost by a charged particle per unit distance traversed in a material. The SI unit of linear energy transfer (LET) is the joule per meter (J m−1). For purposes of radiation protection, LET normally is specified in water and is given in units of keV μm−1. lognormal distribution: A set of values whose logarithms have a normal distribution. lower bound: See lower confidence limit. lower confidence limit: The lowest value in a confidence interval. For example, if (x, y) denotes a 90% confidence interval of an uncertain quantity, the lower confidence limit is x, and since confidence intervals generally are specified symmetrically, the true value is expected to be greater than x in 95% of measurements or predictions (and less than the upper confidence limit y in 95% of cases). See also confidence interval and upper confidence limit. lymphoma: Malignant tumors originating in cells of lymphatic tissues. macular degeneration: A blurring of vision in the central visual field. malignant: Tending to infiltrate, metastasize, and terminate fatally. mean: The arithmetic average of a set of values, given by the sum of the values divided by the number of values. The mean of a distribution of values is the weighted average of possible values, each value weighted by its probability of occurrence in the distribution. mechanical clearance: The remove of inhaled substances from the respiratory tract by processes other than absorption into blood (for example, by ciliary action, coughing, sneezing, or nose-blowing). median: The value in a set of values for which there is an equal probability of a greater or smaller value; the 50th percentile. megaton: A measure of explosive force equivalent to that of 1 million tons of trinitrotoluene (TNT). melanoma: A malignant, and often fatal, tumor in cells of the skin that synthesize dark pigments. metastasis: The transfer of disease from one organ or part to another not directly connected with it due to transfer of cells in malignant tumors. mission badge: A film badge issued to a participant in the atmospheric nuclear-weapons testing program on a particular occasion when unusual potential for exposure to ionizing radiation was expected and intended to be worn only on that occasion. mode: The value in a distribution of values that has the highest probability of occurrence.

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model: A mathematical, or sometimes physical, representation of an environmental or biological system, sometimes including specific values for the parameters of the system. monitoring: The measurement of radiation levels or quantities of radionuclides in environmental media. Monte Carlo analysis: The computation of a probability distribution of an output of a model based on repeated calculations using random samplings of the model’s input parameters (variables) from specified probability distributions. See also Latin hypercube sampling. morning report: A document that records the previous day’s activities of a military unit, including the number of people in the unit and a list of the unit’s officers. mortality: A measure of the number of people who die from a specific disease or condition in a specified population during a specified period. multiple myeloma: The proliferation of plasma cells that often replace all other cells within bone marrow, leading to immune deficiency and, frequently, destruction of the outer layer of bone. neutron: An elementary uncharged particle, of mass slightly greater than that of a proton, that is a constituent of atomic nuclei. noble gas: Any of a group of rare gases (helium, neon, argon, krypton, xenon, and radon) that exhibit great stability and very low chemical reaction rates. nonpresumptive disease: Any radiogenic disease in an atomic veteran that is not presumed in law to have been caused by participation in the atmospheric nuclear-weapons testing program but requires an evaluation of the likelihood that the disease was caused by radiation exposure during such participation. nonrespirable: Incapable of being transported in substantial amounts to regions of the respiratory tract beyond the nose and throat when inhaled, because of the large size of the inhaled materials. normal distribution: A symmetrical and unbounded distribution, often referred to as a “bell-shaped curve,” in which the frequency of occurrence, f, of a distributed quantity, x, is given by where μ is the mean of the distribution and σ2 is the variance. In a normal distribution, the mean, median, and mode are the same. The probability that a value in the distribution lies between any two numbers, a and b, is equal to the area under the curve f(x) between a and b. nuclear weapon: A weapon that derives its explosive force from nuclear fusion or nuclear fission reactions. nucleus: See atomic nucleus.

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operation: See series. parameter: Any of a set of variables in a model whose values determine the characteristics or behavior of the model, especially the model output. An example of a parameter is the resuspension factor in a model to estimate airborne concentrations of radionuclides on the basis of estimated concentrations on a surface. parathyroid adenoma: A benign tumor of glands that are adjacent to or embedded in the thyroid and produce a hormone involved in calcium metabolism. pathway: See exposure pathway. percentile: The value between 0 and 100 that indicates the percent of values in a distribution that are equal to or below it. For example, the 95th percentile is the value that equals or exceeds 95% of the values in a distribution. permanent badge: A film badge issued to a participant in the atmospheric nuclear-weapons testing program that is intended to be worn at all times of potential radiation exposure until the time of turn-in. photon: A quantum of electromagnetic radiation, having no charge or mass, that exhibits both particle and wave behavior, especially a gamma ray or an X ray. positron: A positively charged electron. potential: In the context of dose reconstruction, a term denoting exposure to ionizing radiation (or other hazardous agents) of uncertain occurrence. precision: The degree of reproducibility of a measurement or prediction of a quantity. A measurement or prediction can be precise without being accurate and unbiased. See also accuracy and bias. presumptive disease: Any disease in an atomic veteran that is presumed in law to have been caused by exposure to ionizing radiation during participation in the atmospheric nuclear-weapons testing program without regard for whether radiation exposure occurred during such participation and for the magnitude of any such exposure. probability: The likelihood (chance) that a specified event will occur. Probability can range from 0, indicating that the event is certain not to occur, to 1, indicating that the event is certain to occur. probability distribution: A representation of the likelihood of occurrence of possible values of an uncertain quantity, such as a model parameter or model output. See, for example, lognormal distribution and normal distribution. probability of causation: The probability that a specific disease in a person was caused by their exposure to a particular hazardous agent (such as ionizing radiation). Probability of causation (PC) is estimated as a quotient of two risks: PC = R/(R+B), where R is the estimated risk of the disease in that person due to exposure to the particular hazardous agent and B is the estimated background (baseline) risk of the disease in that person from all other causes (that is, the risk in the absence of exposure to that agent).

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Probability of causation differs from risk in that it is conditional on the occurrence of a disease. See also risk. proton: An elementary particle, with a positive charge numerically equal to the charge of an electron and a mass of 1.672 × 10−27 kg, that is a constituent of atomic nuclei. quadrature: The process of estimating the variance of a quantity calculated as the sum of independent variables by adding the variances of each variable. quality assurance: A process of ensuring proper documentation of data, interpretations of data that are embodied in assumptions, and computer codes. quality control: A process of ensuring that measurements and calculations are free of significant error. quality factor: A dimensionless quantity developed for purposes of radiation protection and assessing risks to human health in general terms that accounts for differences in biological effectiveness between different types of ionizing radiation in producing stochastic effects (such as cancer), which is used to modify the average absorbed dose in an organ or tissue to obtain the average dose equivalent; see ICRP (1977). The quality factor is assumed to be 1 for photons and electrons of any energy, and higher values are assumed for alpha particles and neutrons. Now superseded in radiation protection by the radiation weighting factor. rad: The special name for the conventional unit of absorbed dose; 1 rad = 100 ergs g−1 = 0.01 Gy. radiation: Energy emitted in the form of waves or particles. See also ionizing radiation. radiation effectiveness factor: A dimensionless quantity that represents the relative biological effectiveness of a specific type, and sometimes energy, of ionizing radiation for purposes of estimating cancer risks and probability of causation of specific cancers in persons on the basis of estimates of average absorbed dose from each radiation type in specific organs or tissues in which a cancer has occurred. radiation exposure: See exposure. radiation protection: The control of exposure to ionizing radiation by use of principles, standards, measurements, models, and such other means as restrictions on access to radiation areas or use of radioactive materials, restrictions on releases of radioactive effluents to the environment, and warning signs. Sometimes referred to in the literature as radiological protection. radiation weighting factor: A dimensionless factor developed for purposes of radiation protection and assessing risks to human health in general terms, which is intended to replace the quality factor; see ICRP (1991a). radioactive: Exhibiting radioactivity. radioactive decay: The spontaneous transformation of the nucleus of an atom to a state of lower energy.

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radioactivity: The property or characteristic of an unstable atomic nucleus to spontaneously transform with the emission of energy in the form of radiation. radioepidemiological tables: A tabulation of estimated probabilities of causation of specific cancers in a person at various doses of ionizing radiation. See also probability of causation and risk. radiogenic: Causally linked to or possibly associated with exposure to ionizing radiation. radiological: Of or related to ionizing radiation. radionuclide: A naturally occurring or artificially produced radioactive element or isotope. radiosensitive: Susceptible to the injurious action of ionizing radiation. reconstructed dose: A dose to a person estimated by any means other than a reading of external photon exposure by a film badge worn by the person. Reference Man: A hypothetical aggregation of human physical, anatomical, and physiological characteristics arrived at by international consensus and used in radiation protection for purposes of calculating radiation doses to organs and tissues of the body from external and internal exposure. refractory: Capable of enduring relatively high temperatures (for example, about 3000°C or higher) without boiling. relative biological effectiveness: For a specific radiation (A), the ratio of the absorbed dose of a reference radiation required to produce a specific level of a response in a biological system to the absorbed dose of radiation A required to produce an equal response, with all physical and biological variables, except radiation quality (LET), being held as constant as possible. The reference radiation normally is gamma rays produced in decay of 60Co or 137Cs or X rays produced in an electron tube in which the highest potential difference is about 180–250 kV. RBE is specific to each study and generally depends on the dose, dose per fraction if the dose is fractionated, dose rate, reference radiation, and biological response. rem: The special name for the conventional unit of equivalent dose; 1 rem = 100 ergs g−1 = 0.01 Sv. respirable: Capable of being transported in substantial amounts to regions of the respiratory tract beyond the nose and throat when inhaled, because of the small size of the inhaled materials. respiratory protection: An apparatus, such as a respirator or a mask, used to reduce a person’s intake of airborne materials. respiratory tract: A system of organs subserving breathing and associated functions, consisting of the lungs (bronchial and pulmonary regions), respiratory lymph nodes, and the channels by which these are continuous with the outer air (nose and throat). respiratory-tract model: A biokinetic model describing the deposition, translocation, and absorption of inhaled materials in different regions of the respiratory tract.

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resuspension: The transfer of material that has been deposited on the ground or other surface to the atmosphere; also commonly used to mean suspension of material on the ground or other surface that was not deposited from the atmosphere. resuspension factor: Ratio of the concentration of a resuspended or suspended contaminant in air above the ground or other surface to its concentration on the surface. Resuspension factors usually are determined at a height of 1 m and are given in units of m−1. retention: The act of remaining at a site of deposition in the body. retention half-time: The time required for half the quantity of a radionuclide taken into the body to be eliminated from the body by biological processes and radioactive decay combined; also may be referred to as residence half-time in the literature. risk: The probability of an adverse event. In regard to adverse effects of ionizing radiation on humans, the term usually refers to the probability that a given radiation dose to a person will produce a health effect (such as cancer) or the frequency of health effects produced by given radiation doses to a specified population within a specified period. The risk of cancer due to a given radiation dose generally depends on the cancer type, sex, age at exposure, and time since exposure (attained age), and it may depend on dose rate; the risk of lung cancer also depends on a person’s smoking history, and the risk of melanoma or basal cell carcinoma also depends on a person’s race. roentgen: The special name for the conventional unit of exposure; 1 R = 2.58 × 10−4 coulomb per kilogram (C kg−1). safety shot: A test of a nuclear device in which only conventional explosives are detonated intentionally. Safety shots were carried out to ensure that an accidental triggering of the conventional explosive in a nuclear device would not result in significant nuclear fission. scenario: See exposure scenario. screening: A process of rapidly identifying potentially important radionuclides or exposure pathways by eliminating those of known negligible importance. screening code: A code assigned to military units indicating exposure conditions under which the committed equivalent dose to bone from inhalation of radionuclides should be less than 0.15 rem for personnel in those units. screening dose: A dose to a specific organ or tissue that is assumed to correspond to a 99% upper bound (upper confidence limit) of a probability of causation of 50%. screening model: A model that incorporates pessimistic assumptions about potential exposures to ionizing radiation and a criterion intended to correspond to a negligible dose for the purpose of identifying radionuclides or exposure pathways of negligible importance.

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series: An official grouping of nuclear-weapons tests that were carried out by a military task group over a particular interval and in a particular area (the Nevada Test Site or the Pacific), for example, the PLUMBBOB test series at the NTS in 1957. shielding factor: Ratio of the external exposure rate or dose rate indoors to that outdoors due to attenuation of photon or neutron radiations outside the structure by the structure components. shot: A detonation of a nuclear device; used synonymously with test in the nuclear-weapons testing program. sievert: The special name for the SI unit of equivalent dose; 1 Sv = 1 J kg−1. SI units: See International System of Units. solar index: A whole number between 1 and 10 that represents the intensity of solar ultraviolet radiation at the earth’s surface and is associated with the likelihood of damage to the skin or eye and the time it takes for damage to occur. spectrum: An array of energies of radiation (such as radiation emitted in decay of radionuclides or detonation of nuclear weapons) and their associated intensities. squamous cell carcinoma: A malignant growth originating from plate-like cells found in the outer layer of the skin and usually occurring on the skin, lips, inside of the mouth, throat, or esophagus, which studies have not shown to be radiogenic in humans. standard deviation: Square root of the variance. stochastic: Of, pertaining to, or arising from chance; involving probability; random. stratification: The process or result of separating a sample into subsamples according to specified criteria such as, for example, age, sex, or dose received. surface porosity: The presence of openings on the surface of a material. suspension: See resuspension. systemic: Present in the body after absorption from the respiratory tract, gastrointestinal tract, or skin into blood. test: See shot. tissue weighting factor: A dimensionless factor that represents the ratio of the stochastic risk attributable to a specific organ or tissue to the total stochastic risk attributable to all organs and tissues when the whole body receives a uniform exposure to ionizing radiation; see ICRP (1977; 1991a). toxicant: A poisonous agent. translocation: The movement of a substance from one part of the body to another, especially in blood. transuranium: Of, related to, or being an element with an atomic number greater than that of uranium (92). Examples of transuranium elements are plutonium and americium.

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uncertainty: The lack of sureness or confidence in results of measurements or predictions of quantities owing to stochastic variation or to a lack of knowledge founded on an incomplete characterization, understanding, or measurement of a system. uncertainty analysis: An analysis of the variability in model predictions due to uncertainty in the input parameters or other assumptions. uncertainty factor: In this report, the ratio of an upper confidence limit of an estimated dose to a central estimate. uniform distribution: A probability distribution in which the frequency of occurrence of any value between the lowest and highest possible values is the same. unit dose reconstruction: A reconstruction of radiation doses to an average member of a military unit. upper bound: See upper confidence limit. upper-bound factor: See uncertainty factor. upper confidence limit: The highest value in a confidence interval. For example, if (x, y) denotes a 90% confidence interval of an uncertain quantity, the upper confidence limit is y, and since confidence intervals generally are specified symmetrically, the true value is expected to be less than y in 95% of measurements or predictions (and greater than the lower confidence limit x in 95% of cases). See also confidence interval and lower confidence limit. urinalysis: A method of bioassay involving measurement of quantities of contaminants excreted in urine for the purpose of estimating intake. variability: The variation of a property or quantity among members of a population. Variability is often assumed to be random and can be represented by a probability distribution. variance: A measure of the spread of a distribution of values, denoted by σ2 and given by the mean of the squares of the differences between the individual values and their mean: where μ is the mean of the distribution of values xi, and N is the number of values. See also standard deviation. volatile: Capable of boiling at relatively low temperatures (for example, about 1500°C or lower). weathering: (A) A reduction in availability of material deposited on the ground or other surfaces for resuspension, owing to physical, chemical, or biological processes other than radioactive decay. (B) Actions of the weather (wind, precipitation, or temperature changes) to reduce the size of particles deposited on the ground or other surfaces or to cause radionuclides present in the uppermost soil layer to migrate to greater depth.

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whole body: For purposes of estimating radiation dose, especially from external exposure, the head, trunk (including male gonads), arms above the elbow, and legs above the knee. whole-body counting: The measurement of radioactivity in the body by use of radiation detectors outside the body to detect penetrating radiation (gamma rays and x rays) emitted by the sources. X radiation: (A) Electromagnetic radiation emitted in de-excitation of bound atomic electrons, frequently occurring in decay of radionuclides, referred to as characteristic X rays, or (B) electromagnetic radiation produced in deceleration of energetic charged particles (such as beta radiation) in passing through matter, referred to as continuous X rays or bremsstrahlung; also called X rays. See gamma radiation and photon. yield: The total energy released in a nuclear detonation, usually expressed in kilotons (kT) or megatons (MT). The announced yield includes the energy released by fission and fusion.