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, 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 conventional units used in this report, absorbed dose is given in rads; 1 rad = 0.01 Gy.

Benign tumor: 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.

Cancer: A malignant tumor of potentially unlimited growth that expands locally by invasion and systemically by metastasis.

Carcinogen: An agent capable of inducing cancer.

Contaminant: 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.

Dirty bomb: 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 gdirty.h Such bombs could be miniature devices or as big as a truck bomb.

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. Units are rad, mrad, gray, or mgray.

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 Now superseded by effective dose.

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.

Epidemiologic studies: 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.

Equivalent dose: 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.

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).

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.

Fission: 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.

Goiter: An enlargement of the thyroid gland.

Hot spot: The region in a radiation/contamination area in which the level of radiation/contamination is noticeably greater than in neighboring regions in the area.

Hyperparathyroidism: Disorder that is characterized by the excessive production of parathyroid hormones.

Hyperthyroidism: Disorder that is characterized by the excessive production of thyroid hormones.

Internal dose: The dose to organs or tissues of the body due to sources of ionizing radiation within the body.

Iodine-131 (131I): 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 humans 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).

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).

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.

Nuclear emergency: An emergency that has led, or could lead, to a radiological threat to public health and safety, property, or the environment.

Nuclear facility: 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 reactor or plants.

Nuclear incident: 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.

Organ dose: The energy absorbed in a specific organ divided by its mass. This quantity is expressed in gray (Gy) or its submultiples.

Plume: 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.

Protective measures: 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.

Radiation: Energy emitted in the form of waves or particles.

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 as radiological protection.

Radioactivity: The property or characteristic of an unstable atomic nucleus to spontaneously transform with the emission of energy in the form of radiation.

Radionuclide: A naturally occurring or artificially produced radioactive element or isotope.

Release: The controlled or accidental discharge of radioactive substances into the atmosphere or water that may occur during the operation of nuclear facility.

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.

Thyroid blocking agent: A substance that prevents or reduces the uptake of radioactive iodine by the thyroid. See potassium iodide.

Thyroid palpation: The procedure in which a physician characterizes the size, shape, and texture of the thyroid gland by manual examination of the neck.

Thyroiditis: Inflammation of the thyroid gland; may involve an enlarged thyroid and hypothyroidism and may require lifelong therapy with thyroid hormone.