DEFINITION
Ionizing radiation consists of particles and electromagnetic waves that have sufficient energy to interact with matter, including living tissues, to produce charged particles, or ions (Hobbs and McClellan 1986, UNESCAR 1988).
Radioactive material includes elements and isotopes with unstable nuclei
that spontaneously disintegrate, or decay, releasing ionizing radiation
in the process. The decay products from this process, or daughter
radionuclides, may be stable isotopes or may themselves be radioactive.
The physical half-life of a radionuclide is defined as the time required
for the decay of half of a given number of atoms of the radionuclide.
Nuclides are forms of an element that have different atomic and mass numbers.
Radionuclides are radioactive nuclides. The five types of ionizing
radiation include three particles: alpha particles, beta particles, and
neutrons; and two waves: gamma rays, and X-rays.
CHARACTERISTICS OF THE FIVE TYPES OF IONIZING RADIATION
Alpha particles consist of two protons and two neutrons, and carry a charge of +2. Because of their double charge and large mass, they have relatively weak ability to penetrate matter, and a single sheet of paper provides adequate shielding. However, they interact strongly with the matter they do penetrate, and generate a large number of ions. Heavy (transuranic) elements such as uranium, plutonium, and radium are the primary emitters of alpha particles (Hoffman et al. 1995).
Beta particles typically consist of (negatively charged) electrons, emitted in the radioactive decay of many radionuclides. Positively charged beta particles, called positrons, occur less commonly. Beta particles have somewhat more penetrating ability than alpha particles, but 3 mm of metal or 6 mm of wood provide effective shielding. Many of the relatively light radionuclides (e.g., 14C, 24Na, 38Mg, 39Ar, 40K, 87Rb, 90Sr) typically emit beta particles during decay (Hoffman et al. 1995).
Neutrons consist of a proton and an electron. They have a mass very close to that of an electron and no electrical charge. These characteristics produce great energy and high penetration. Neutron radiation results from spontaneous fission, and from fission chain reactions when certain elements are bombarded with neutrons in production reactors (Hoffman et al. 1995). Even eight inches of steel would have little shielding effect against neutron radiation (Nelson and Wodrich 1974).
Gamma rays are waves of energy emitted by nuclei. These waves have wavelengths of less than about 10-12m, no mass, and no charge. They are highly penetrating, and require 5-10 cm of lead or 30-60 cm of concrete to provide adequate shielding. A large number of radionuclides emit gamma rays, usually in combination with alpha or beta particles (Hoffman et al. 1995).
X-rays are waves of energy with wavelengths of 10-8 m to somewhat longer than 10-12 m that are emitted by the electron shells of certain radionuclides, such as iron-55. X-rays also can be produced by specialized high voltage equipment without the involvement of radioactive material. Various thicknesses of platinum, aluminum, and lead provide effective shielding from X-rays (Donzetti 1967).
Bacground Radiation: Natural sources of radiation include: (a) cosmic radiation, originating in outer space; (b) terrestrial radiation from naturally-occurring radionuclides (including radon gas) in rocks, soils, and sediments; and, for animals, (c) internal radiation from food consumption (primarily potassium-40)(Hoffman et al. 1995). Natural background radiation varies geographically over the earth. Cosmic radiation levels increases with increasing altitude, while terrestrial radiation levels vary with the composition of bedrock. Levels of cosmic and terrestrial radiation in New Hampshire also vary geographically, but overall are close to national averages (See Table 1). Appendix I lists the most abundant naturally-occurring radionuclides.
Table 1. Estimated annual whole body doses of background radiation
(expressed as mrem/person) Radiological quality of the
Environment in the United States, 1977. U.S. Environmental Protection
Agency, Office of Radiation Programs. 295 pp.
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History of Human Applicatoins (Summarized from Kathren 1984 and Burns 1988): Radioactivity has been known to humanity for just over 100 years. W.C. Roentgen, in Germany, discovered X-rays in November 1895. Discovery of natural radioactivity, by Antoine Becquerel in France, followed in early 1896. Marie Curie hypothesized that the emissions from uranium that Becquerel had observed resulted from structural changes within the atoms themselves, and, with her husband Pierre, subsequently discovered the radioactive elements polonium and radium in 1898.
The diagnostic value of X-rays was immediately apparent. The technology was quick to cross the Atlantic, and an astronomer at Dartmouth College made the first diagnosis by X-ray in North America in February 1896. While some hospitals were slow to accept X-ray diagnosis, X-ray use was routine by 1917.
Several scientists observed the effects of cosmic rays in 1900, and Victor Hess first recognized their extraterrestrial origin about a decade later. Robert A. Milliken conclusively established the origin of cosmic rays in 1925.
Irene Joliot-Curie and her husband Frederic Joliot discovered that bombardment of some stable nuclei with neutrons created new radioisotopes, enabling the subsequent synthesis of nearly 100 nonnatural radioisotopes within a year's time. The concept of a self-sustaining nuclear reaction was first described in 1934, and the process of fission discovered in 1938.
The Manhattan Project, which developed an atomic bomb for the World War II Allies, commenced in 1942, and the first controlled chain reaction was generated later that year. Detonation of the first atomic bomb occurred in New Mexico in July 1945, and bombs were subsequently dropped on Hiroshima and Nagasaki in August 1945. Following the war, the U.S. government retained tight control on atomic energy technology until the Atomic Energy Act of 1954 permitted development of nonmilitary applications, leading to construction of commercial nuclear power plants, the development of nuclear medicine, and various industrial applications.
History of Federal Regulation (summarized from Jordan 1984): The Atomic Energy Act of 1946 (Chapter 724, August 1, 1946) vested ultimate responsibility for regulation of radioactive materials in the federal government. The Atomic Energy Act of 1954 (Chapter 1073, August 30, 1954) reiterated this responsibility and established the Atomic Energy Commission (AEC). A 1959 amendment authorized state governors to enter into agreements with the AEC to regulate some types and quantities of radioactive materials provided that state standards and regulations were compatible with those of AEC. New Hampshire subsequently entered into such an agreement in May 1966. The Energy Reorganization Act of 1974 created the Energy Research and Development Administration (ERDA) and the Nuclear Regulatory Commission (NRC) from what had been the AEC, separating development and regulatory responsibilities between the two new agencies. ERDA became part of the Department of Energy (DOE) in 1977. The Low-Level Radioactive Waste Policy Act (LLRWPA) of 1980 (Public Law 96-576) gave states responsibility for disposing of LLRW generated within their boundaries, and authorized states to enter into compacts to establish and operate regional disposal sites as the safest and most efficient management option.
At the present time, four federal agencies are involved in various aspects of the regulation and management of ionizing radiation. The Nuclear Regulatory Commission (NRC) licenses and regulates commercial nuclear power reactors, and individuals and organizations that possess and use certain radioactive materials; regulates LLRW in non-agreement states; and ensures the compatibility of state and federal regulatory programs. The Department of Energy (DOE) is the lead agency in planning and coordination of a national system for management and disposal of HLRW; assists states and regions in developing compacts for regional LLRW disposal facilities; develops and transfers pertinent technology; and operates and regulates disposal facilities for defense-generated radioactive wastes. The Department of Transportation (DOT) regulates interstate transportation of hazardous materials, including radioactive materials. The Environmental Protection Agency (EPA) establishes standards and criteria to protect the environment from effects of anthropogenically derived radiation through the provisions of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980 (CERCLA) (Public Law 96-510).
In addition, the U.S. Geological Survey (USGS) provides advice to state and federal agencies regarding geological aspects of disposal facility siting and construction, and the U.S. Fish and Wildlife Service (USFWS) reviews and comments on federal actions that can affect fish and wildlife resources. The Biological Resources Division of the USGS (formerly the National Biological Service in the Department of Interior, and previously the research branch of the USFWS) compiles information on radionuclide contamination of fish and wildlife and their habitats.
State Regulation: The New Hampshire Bureau of Radiological Health (NHBRH) regulates all sources of radiation in the state, licenses users of radioactive materials under agreement with the Nuclear Regulatory Commission, inspects licensees, investigates reported incidents involving radioactive materials, conducts environmental monitoring, provides emergency response, regulates disposal of LLRW, and co-regulates disposal of mixed waste under a memorandum of agreement with the NH Department of Environmental Services. (NHBRH also registers and licenses X-ray machines and linear accelerators, which generate radiation while operating, but do not contain radioactive material.)
Local Antropogenic Sources: Anthropogenic sources of radiation
in New Hampshire include nuclear power plants in Seabrook, NH and Brattleboro,
Vermont (on the Vermont-New Hampshire border); transportation, storage
and use of radionuclides for medicinal, industrial, and research applications;
and fallout from nuclear weapons tests, nuclear accidents, and operational
emissions in distant locations.
Units of Measurement
Measures of radioactivity
(Ci) curie: historical unit of radioactivity 37 billion
disintegrations per second (the number of radioactive disintegrations per
second by one gram of radium)
(BQ) becquerel: International System of Units radioactivity unit, equals 2.7 x 10-11 curies, or one disintegration per second
Measures of radiation dose
(rem) roentgen equivalent man: historic unit of radiation
dose for humans
(Sv) sievert: International System of Units radiation dose equivalent unit, equals 100 rem
Measures of absorbed radiation dose
(rad) radiation absorbed dose: historic unit of absorbed
radiation
(Gy) gray: International System of Units absorbed radiation dose unit, equals one joule per kilogram, or 100 rad
(m[unit]) milli[unit]: 0.0001[unit] e.g.,(mrem)milliroentgen:
0.0001 rem
References
Burns, M.E. 1988. Low-level Radioactive Waste Regulation; Science, Politics and Fear. Lewis Publishers, Inc., Chelsea, MI. 311 pp.
Donzetti, P., translated by A. Ellis. 1967. Shadow and Substance; The Story of Medical Radiography. Pergammon Press, New York.
Eisenbud, M. 1973. Environmental Radioactivity. Academic Press, NY
Hobbs, C.H. and R.O. McClellan. 1986. Toxic effects of radiation and radioactive materials. Pp. 669-705 in C.D. Klassen, M.O. Amdur, and J. Doull, eds. Casarett and Doull's Toxicology. 3rd edition. Macmillan, NY.
Hoffman, D.J., B.A. Rattner, G.A. Burton, Jr., and J. Cairns, Jr. 1995. Handbook of Ecotoxicology. Lewis Publishers, London.
Jordan, J.M. 1984. Low-level radioactive waste management: an update. A Legislator's Guide. National conference of State Legislatures. Denver, CO and Washington, D.C.
Kathren, R.L. 1984. Radioactivity in the Environment. Harwood Academic Publishers, New York.
Nelson, D.C. and D.D. Wodrich. 1974. Retrievable Surface Storage Facility for Commercial High Level Waste. Atlantic-Richfield Hanford Company, ARH-SA-175 (April), Hanford, WA.
United Nations Scientific Committee on the Effects of Atomic Radiation. (UNSCEAR) 1988. Sources, Effects, and Risks of Ionizing Radiation. United Nations, New York.
United States Environmental Protection Agency (USEPA). 1977. Radiological Quality of the Environment in the United States, 1977. U.S. Environmental Protection Agency, Office of Radiation Programs, EPA 520/1-77-09.
Appendix I. Natural radionuclides that occur in significant
amounts in nature. Eisenbud, M. 1973. Environmental Radioactivity.
Academic Press, New York.
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Note: The following two technical reports address:
(a) Non-Reactor Sources of Radiation (Low Level Radioactive Waste and Non-Reactor Radioactive Materials) and
(b) Nuclear Reactors and Associated Radioactive Waste (Seabrook and Vermont Yankee nuclear power plants and Portsmouth Naval Shipyard) respectively.