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, equal to 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 this report, absorbed dose is given in rads; 1 rad = 0.01 Gy.
The production of radionuclides by capture of radiation (for example, neutrons) in atomic nuclei.
The rate of transformation (or disintegration 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 this report, activity is given in curies (Ci); 1 Ci = 3.7 × 1010 Bq.
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.
Averted (or avertable) dose:
The dose to be prevented by the particular protective action (i.e., the difference between the dose to be expected without stable iodine blockade and that to be expected with it).
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.
The special name for the SI unit of activity; 1 Bq = 1 disintegration per second.
A general category of tumors that does not invade surrounding tissue. Benign tumors are characterized by slow growth through expansion. Such tumors are not malignant or cancerous.
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.
A malignant tumor of potentially unlimited growth that expands locally by invasion and systemically by metastasis.
An agent capable of inducing cancer.
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.
A group of individuals having a common association or factor.
Committed dose equivalent (CDE):
The dose equivalent to organs or tissues of reference that will be received from an intake of radioactive material by an individual during the 50-year period following intake.
Committed effective dose equivalent (CEDE):
The sum of the products of the weighting factors applicable to each of the body organs or tissues that are irradiated and the committed dose equivalent (CDE) to each of these organs or tissues. This is a measure of the overall risk associated with internal deposition of radioactive material.
A gas-tight shell or other enclosure around a nuclear reactor to confine radioactive materials that otherwise might be released to the atmosphere in the event of an accident.
The central portion of a nuclear reactor containing the fuel elements, moderator, neutron poisons and support structures.
Most generally, the degree to which one phenomenon or variable is associated with or can be predicted from another. In statistics, usually refers to the degree to which a predictive relationship exists between variables. Correlation may be positive (both variables increase or decrease together) or negative or inverse (one variable increases when the other decreases).
The conventional unit of radioactivity, equal to 3.7 × 1010 Bq.
Deep dose equivalent (DDE):
The dose equivalent at a tissue depth of 1 cm; applies to external exposure.
A postulated accident that a nuclear facility must be designed and built to withstand without loss to the systems, structures and components necessary to assure public health and safety.
Also known as a radiological weapon or radiological dispersion device, this is a conventional explosive such as dynamite packaged with radioactive material that scatters when the bomb goes off. A dirty bomb kills or injures through the initial blast of the conventional explosive and by airborne radiation and contamination—hence the term “dirty.” Such bombs could be miniature devices or as big as a truck bomb.
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. Units are rad, mrad, gray, or mgray.
A portable instrument for measuring and registering the total accumulated exposure to ionizing radiation.
The sum over specified organs or tissues of the equivalent dose in each tissue modified by the tissue weighting factor, as defined in ICRP (1991). 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.
A substance that cannot be separated by ordinary chemical methods. Elements are distinguished by the numbers of protons in the nuclei of their atoms.
Emergency planning zone:
An area around a nuclear facility for which detailed planning and preparation are made in advance to ensure that appropriate protective measures can be applied in a timely and accurate manner.
Studies designed to examine associations—commonly, hypothesized causal relations. They are usually concerned with identifying or measuring the effects of risk factors or exposures. The common types of epidemiologic
studies are case-control studies, cohort studies, and cross-sectional studies.
The study of the incidence, distribution, and causes of health conditions and events in populations.
A quantity obtained by multiplying the absorbed dose by a radiation-weighting factor to allow for the different effectiveness of the various types of ionizing radiations in causing late effect harm in tissue. The equivalent dose is theoretical and has replaced the earlier dose equivalent. The equivalent dose is often expressed in sievert (Sv). It is also sometimes expressed in rem (an older unit). One hundred rem equals 1 Sv.
A measure of or statement about the value of a quantity that is known, believed, or suspected to incorporate some degree of error.
A protective measure in which individuals must leave their homes quickly, stay away for a limited period of time, to avoid or reduce radiation 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.
The physical course of a radionuclide or other hazardous agent from its source to an exposed person.
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).
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.
The splitting of a nucleus into at least two other nuclei and the release of a relatively large amount of energy. Two or three neutrons are usually released during this type of transformation.
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.
An enlargement of the thyroid gland.
The special name for the SI unit of absorbed dose; 1 Gy = 1 J kg-1 = 100 rad.
The average time it takes for one-half of any given number of unstable atoms to decay. Half-lives of isotopes range from small fractions of a second to more than a billion years. As an example, if on average 100 out of 200 radioactive atoms of a specified kind decay in 1 day (half-life=1 day), then of the remaining 100 atoms, 50 would be expected to decay during the second day. Similarly, 25 of the remaining 50 atoms would be expected to decay during the third day. This type of decay is called exponential.
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.
The time required for the activity of a radioactive substance in the body to decrease to 1/2 its value due to the combined effects of biological elimination and radioactive decay. The effective half-life facilitates evaluating radiation dose from inhaled and ingested radionuclides and applies when the biological and physical half-lives are constant. For an effective half-life of 1 hour, 1/2 of the radioactivity would be expected to be eliminated during the first hour. Of the radioactivity that remained, 1/2 would be expected to be eliminated during the second hour. This
represents 1/4 of the initial radioactivity present. Thus, for each successive hour, the expected fractions of the initial radioactivity present that are eliminated would be 1/2, 1/4, 1/8 and so on. This type of decrease over time is called exponential.
See half-life, physical.
The region in a radiation/contamination area in which the level of radiation/contamination is noticeably greater than in neighboring regions in the area.
Disorder that is characterized by the excessive production of parathyroid hormones.
Disorder that is characterized by the excessive production of thyroid hormones.
The International Atomic Energy Agency, one of the specialized bodies of the United Nations charged with the responsibility of overseeing and setting standards and recommendations for the operation of nuclear activities and for radiation safety in the member states. It is headquartered in Vienna, Austria, and its members have played a major role in the accumulation and dissemination of the information derived from the Chornobyl accident as well as other accidents involving exposure to ionizing radiation.
The rate of occurrence of new cases of a specific disease in a specific time period, 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.
This guidance distinguishes three phases of an incident (or accident). Early phase, the period at the beginning of a nuclear incident when immediate decisions for effective use of protective actions are required, and must be based primarily on predictions of radiological conditions in the environment. This phase may last from hours to days. For the purpose of dose projection, it is assumed to last for four days. Intermediate phase, the period beginning after the incident source and releases have been brought under control and reliable environmental measurements are available for use as a basis for decisions on additional protective actions and
extending until these protective actions are terminated. This phase may overlap the early and late phases and may last from weeks to many months. For the purpose of dose projection, it is assumed to last for one year. Late phase, also referred to as the recovery phase: the period beginning when recovery action designed to reduce radiation levels in the environment to permanently acceptable levels are commenced, and ending when all recovery actions have been completed. This period may extend from months to years.
The dose to organs or tissues of the body due to sources of ionizing radiation within the body.
International System of Units:
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), also referred to as SI units.
A radioactive isotope of iodine. Iodine is an element required in small amounts for healthy growth and development. It is mainly concentrated in the thyroid gland where it is needed to synthesize thyroid hormones. 131I is used as a radioactive tracer in nuclear medicine and is found in fallout from nuclear testing. 131I has been demonstrated to cause thyroid cancer in children after moderate and high doses following the Chornobyl accident. Whether very low radiation doses cause thyroid cancer is uncertain. Iodine-131 has a relatively short physical half-life (8 days).
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).
To expose to radiation.
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.
See potassium iodide.
The earliest time after exposure to a carcinogenic agent when a cancer caused by that exposure can occur; also called latency period.
The term used to describe a group of malignant, commonly fatal blood diseases characterized by an uncontrolled increase in the number of white cells (generally their immature forms) in the circulating blood.
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.
The spread of cancer from one organ or part to another part not directly connected with it through transfer of malignant cells.
A construct (generally mathematical) that attempts to describe the events that underlie some biological or physical phenomenon of interest, such as the occurrence of cancer following exposure to ionizing radiation.
A measure of a diseased condition or state; refers to illness, not death.
A measure of the number of people who die from a specific disease or condition.
National Academy of Sciences. The National Academy of Sciences is a private, non-profit, self-perpetuating society of distinguished scholars engaged in scientific research. Upon the authority of the charter granted by the Congress in 1863, the NAS has a mandate that requires it to advise the federal government on scientific and technical matters.
National Research Council. The NRC is the principal operating agency of the National Academy of Sciences and the National Academy of Engineering to serve the federal government and other organizations.
Any new or abnormal growth, such as a tumor; neoplastic disease refers to any disease that forms tumors, whether malignant or benign.
An elementary uncharged particle, of mass slightly greater than that of a proton that is a constituent of atomic nuclei.
An emergency that has led, or could lead, to a radiological threat to public health and safety, property, or the environment.
A nuclear reactor, research reactor, or plant for the separation, processing, reprocessing, or fabrication of fissionable substances from irradiated fuel. It also includes all land, buildings and equipment that are connected or associated with these reactors or plants.
An event or series of events, either deliberate or accidental, leading to the release, or potential release, into the environment of radioactive materials in sufficient quantity to warrant consideration of protective actions.
Nuclear power plant:
An electrical generating facility using a nuclear reactor as its heat source to provide steam to a turbine generator.
The energy absorbed in a specific organ divided by its mass. This quantity is expressed in gray (Gy) or its submultiples.
A cloud of airborne radioactive material that is transported from a nuclear or radiological source in the direction of the prevailing wind.
Potassium iodide (KI):
Colorless or white crystals, having a faint odor of iodine; used as a "blocking agent" to prevent the human thyroid gland from absorbing radioactive iodine.
The number of cases of a specific disease existing in a particular population or area at a certain time. The value is different numerically from incidence.
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.
Measures taken to reduce radiation doses that could be incurred by the population or emergency workers during a nuclear emergency. Also referred to as a countermeasure or protective action.
The special name for the conventional unit of absorbed dose; 1 rad = 100 ergs g-1 = 0.01 Gy.
Energy emitted in the form of waves or particles. See also ionizing radiation.
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 as radiological protection.
The spontaneous transformation of the nucleus of an atom to a state of lower energy.
The property or characteristic of an unstable atomic nucleus to spontaneously transform with the emission of energy in the form of radiation.
Causally linked to or possibly associated with exposure to ionizing radiation.
A naturally occurring or artificially produced radioactive element or isotope.
Reactor coolant system:
The cooling system used to remove energy from the reactor core and transfer that energy either directly or indirectly to the steam turbine.
The controlled or accidental discharge of radioactive substances into the atmosphere or water that may occur during the operation of nuclear facility.
The special name for the conventional unit of equivalent dose; 1 rem = 100 ergs g-1 = 0.01 Sv = 10 mSv. For gamma and beta radiation and x rays, 1 rem = 1 rad = 0.01 Gy = 10 mGy.
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 ratio of the risk in one population to that in another; for example, the ratio of the risk among individuals exposed to 2 Gy as contrasted with the background risk.
The special name for the conventional unit of exposure; 1 R = 2.58 × 10-4 coulomb per kilogram (C kg-1).
A protective measure that consists of staying indoors, with closed doors and windows, to limit the inhalation of radioactive products that may present following a release of radiation, or to protect against direct gamma radiation from a radioactive cloud, or from radioactive material deposited on the ground.
The special name for the SI unit of equivalent dose; 1 Sv = 1 J kg-1 = 100 rem.
See International System of Units.
An isotope of iodine that does not undergo radioactive decay.
Thyroid blocking agent:
A substance that prevents or reduces the uptake of radioactive iodine by the thyroid. See potassium iodide.
The total activity of a radionuclide in the thyroid.
The procedure in which a physician characterizes the size, shape, and texture of the thyroid gland by manual examination of the neck.
Inflammation of the thyroid gland; may involve an enlarged thyroid and hypothyroidism and may require lifelong therapy with thyroid hormone.
Total effective dose equivalent (TEDE):
The sum of the deep dose equivalent (DDE) for external exposures and the committed effective dose equivalent (CEDE) for internal exposures.
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.
The United Nations Scientific Committee on the Effects of Atomic Radiation, one of the specialized bodies of the
United Nations charged with the responsibility of evaluating the effects of exposure to atomic (ionizing) radiation on behalf of the member nations.
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.
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.
W-C Effect (Wolff-Chaikoff Effect):
Blocking of the organic binding of iodine and its incorporation into hormone caused by large doses of iodine; usually a transient effect, but in large doses in susceptible individuals it can be prolonged and cause iodine induced hypothyroidism.
(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.
Conversions between SI units and Traditional Units
Special name of SI unit
coulomb per kilogram (C kg-1)
1 R = 2.58 10-4 C kg-1
joules per kilogram (J kg-1)
1 rad = 0.01 Gy
joules per kilogram (J kg-1)
1 rem = 0.01 Sv
disintegrations per second (s-1)
1 Ci = 3.7 1010 Bq
LIST OF ABBREVIATIONS
American Academy of Pediatrics
Atomic Energy Commission
American Thyroid Association
Committed Dose Equivalent
Committed Effective Dose Equivalent
Conference of Radiation Control Program Directors, Inc.
Design Basis Accident
U.S. Department of Health and Human Services
U.S. Department of Homeland Security
U.S. Department of Defense
U.S. Department of Energy
U.S. Environmental Protection Agency
Emergency Planning Zone
Food and Drug Administration
Federal Emergency Management Agency
International Atomic Energy Agency
International Commission on Radiological Protection
International Commission on Radiation Units and Measurements
Institute of Medicine
Linear Energy Transfer
National Academy of Sciences
National Cancer Institute
National Council on Radiation Protection and Measurements
Nuclear Energy Agency
Nuclear Energy Institute
National Emergency Management Association
National Institutes of Health
National Institute for Occupational Safety and Health
Nuclear Power Plant
U.S. Nuclear Regulatory Commission
Office of Science and Technology Policy
Protective Action Guideline
Pilot Operated Relief Valve
Radioactive Iodine Uptake
Radiation Effectiveness Factor
Radiation Emergency Assistance Center/Training Site
Radiological Emergency Preparedness
Système International (International System)
Thyroid-Hormone Binding Globulin
Thyroid Hormone Triiodothyronine
Thyroid Hormone Thyroxine
Total Effective Dose Equivalent
World Health Organization