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curie: A measure of radioactivity. One curie of radioactive material will have 37 billion transformations of atoms (disintegrations) in one second. One curie of radium weighs approximately one gram.
disposal: Isolation of radioactive waste separated from the accessible environment with no intent of recovery; occurs when a repository is sealed.
half-life: Measure of the amount of time it takes for half the radioactive atoms in a radionuclide to decay to a more stable form. The half-life of plutonium-239, for example, is about 24,000 years. After one half-life, half the radioactive atoms in a sample remain radioactive; after two half-lives, one-quarter of the original number remain radioactive; after three half lives, one-eighth of the original number remain radioactive; and so on. Half-lives range from a fraction of a second to billions of years.
hazardous waste: A solid waste, or combination of solid wastes, which because of its quantity, concentration, physical or chemical characteristics may (1) cause, or significantly contribute to, an increase in mortality or an increase in serious irreversible, or incapacitating but reversible serious illness or (2) pose a substantial present or potential hazard to human health or the environment when improperly treated, stored, transported, disposed of, or otherwise managed.
ionizing radiation: Radiation that is powerful enough to alter atoms by removing one or more electrons, leaving positively charged particles. Alpha and beta particles, gamma rays, and x-rays are forms of ionizing radiation.
millirem: One one-thousandth of a rem. One one-thousandth of a rem.
NARM/NORM: Naturally Occurring and Accelerator-Produced Radioactive Materials (NARM) include by-products of petroleum production, coal ash, phosphate fertilizer production, drinking water treatment, and other industrial processes. NORM is a subset of NARM and includes everything in NARM except accelator-produced materials. The federal government has not developed a comprehensive policy for NORM/NARM disposal.
nonionizing radiation: Includes visible light, ultraviolet light, infrared light, and radio waves.
orphan sources: found or abandoned sources of contaminated materials in which identifying marks have been removed or damaged therefore not easily traceable or detectable.
Rad (radiation absorbed dose): The amount of ionizing radiation absorbed by a material, such as human tissue.
radiation: Energy in the form of high-speed particles (ionizing) or electromagnetic waves (nonionizing).
Radioactive contamination: Deposition of radioactive material in any place where it may harm persons, equipment, or the environment.
radioactivity: The spontaneous emission of radiation from the nucleus of an atom. Radioisotopes of elements lose particles and energy through the process of radioactive decay.
rem (Roentgen equivalent man): A measure of the actual biological effects of radiation absorbed in human tissue. A millirem is one one-thousandth of a rem.
roentgen: A measure of exposure; it describes the amount of radiation energy, in the form of gamma or x-rays, deposited in the air.
All definitions except those noted below reproduced from A Reporter’s Guide to Yucca Mountain, with permission from the Environmental Health Center of the National Safety Council. Definitions of "NARM/NORM" and "Radioactive contamination" reproduced from Understanding Radiation in Our World, with permission from the Environmental Heath Center of the National Safety Council.
Definition of "orphan source" complied with information from RadTown USA, a website published by the EPA (http://www.epa.gov/radtown/orphan-sources.html).
