3. What Are the Sources of Ionizing Radiation? aturally occurring radioactive materials Natural Sources of Radiation Nare common in the environment and in ➤ Radon the human body. These materials are continu- The largest natural source of radiation ously emitting ionizing radiation. Ionizing exposure to humans is radon gas. While radon radiation from outer space (cosmic radiation) gas has always been in the environment, bombards the earth constantly. The ionizing awareness of its contribution to human radiation from these and similar natural radiation exposure has increased in recent sources is called background radiation. years. Radon's primary pathway is through air Human activities, such as making medical x- space in soil and rock. Pressure differences rays, generating electricity from nuclear between the soil and the inside of buildings power, testing nuclear weapons, and produc- may cause radon gas to move indoors. ing a variety of common products such as Depending on source strength and other smoke detectors which contain radioactive variables, unacceptable amounts of radon gas materials, can cause additional exposure to can accumulate indoors, where building ionizing radiation. occupants will be exposed to the ionizing The percentage of the average annual radiation emitted by radon and its decay radiation exposure contributed by each major products. The average American receives source is illustrated in Figure 1. The total is about 200 millirem (mrem) per year from about 360 millirems. About 82 percent is from radon. nature; 18 percent is from industrial, medical, Radon concentrations can vary depending and consumer sources. The values given in on the soil and rock composition beneath Figure 1 are averages for the United States. buildings. The northwestern part of New Actual values vary, depending on where Jersey is part of the "Reading Prong", a people live and how they spend their time. geological region with a high granite content. This Fact Sheet describes sources of Granite can contain higher than average ionizing radiation and gives some reasons for amounts of uranium, which decays to radon the variations in radiation exposure received. gas. Many people who live over this geological formation experience higher doses from radon than those who live elsewhere in New Jersey. Exposure due to Exposure due to natural sources human activities Radon 200mrem (55%) Medical/Dental X-rays 39mrem (11%) Inside Human Body 40mrem (11%) Nuclear Medicine 14mrem (4%) Rocks & Soil 28mrem (8%) Consumer Products 10mrem (3%) Cosmic 27mrem (8%) Other (<1%) Figure 1. Average Annual Exposure to Ionizing Radiation in U.S.A. Page 2 • What are the Sources of Ionizing Radiation? ➤ Internal Radiation Medical and Consumer Internal radiation comes from radioactive Product Sources materials that occur naturally in the human ➤ Medical Sources body. Isotopes of potassium and carbon are The largest source of medical exposure, when the primary sources of internal radiation averaged over all individuals, is from diagnos- exposures. tic x-rays, including both chest or limb x-rays Potassium is an essential mineral for life. and dental x-rays. The Potassium-40 isotope (0.01 percent of all Other sources are lumped into the category potassium) is naturally radioactive. Carbon of nuclear medicine. These include diagnostic makes up about 23 percent, by weight, of the procedures that use nuclear tracers. (Very human body. Cosmic radiation creates small amounts of radioactive materials, called radioactive Carbon-14, which is an even tracers, are put into the blood stream, and smaller percentage of all carbon. their progress through the body is monitored Potassium and carbon enter the body with a radiation detector. Blocked or re- through the food chain. The average Ameri- stricted blood vessels can be identified, as can can receives a dose of about 40 mrem per year developing tumors.) Nuclear medicine also from internal radiation. includes treatment of disease. Some examples are cobalt irradiation for the treatment of ➤ Other Terrestrial Sources cancers, or the injection of radioactive iodine Other terrestrial sources include naturally which concentrates in the thyroid for treat- occurring radioactive materials that exist in ment of Graves’ disease. The annual dose for rocks and soil. The main contributors are the the average American is about 53 mrem from radioactive isotopes that are products of the medical sources. decay of uranium and thorium. The average American receives about 28 mrem per year ➤ Consumer Products from terrestrial sources. Radiation is used in the manufacturing of many consumer products. It is used to ➤ Cosmic Radiation sterilize products such as cosmetics and As the earth moves through space it is medical supplies and for shrink-wrap packag- bombarded by high-energy particles and ing. It can be used to determine the thickness gamma rays, which add to the background of materials, how full cans are before sealing radiation. The earth’s atmosphere acts as a them, and the quality of welds in structures shield, absorbing much of the energy from such as bridges and buildings. This use of cosmic radiation. People who live close to sea radiation can expose workers in the factory, level are protected by a thicker blanket of but it does not make the consumer product atmosphere than those who live at high radioactive. elevations, and thus have a lower exposure to Radioactive materials also are used in cosmic radiation. For example, the exposure many consumer products. The most common to cosmic radiation is about twice as high in of these is some smoke detectors which use Denver as it is in Atlantic City. radioactive Americium-241 to detect smoke particles in the air. What are the Sources of Ionizing Radiation? • Page 3 Some consumer products naturally ➤ For More Information contain radioactive materials. They include If you want to read more about sources of tobacco products, natural gas, phosphate ionizing radiation, some of the references and fertilizers, some brick or stone construction other Fact Sheets listed below may be materials, gas mantles, some luminous signs, helpful. and certain ceramics. • Eric J. Hall, Radiation and Life, Second The dose from medical, industrial, and Edition, Pergamon Press, New York, 1984. consumer product sources varies from person • Fred A. Mettler, Jr. and Robert D. Moseley, to person, depending upon such factors as Jr., Medical Effects of Ionizing Radiation, type of home, type of employment, smoking Grune & Stratton, Inc., Orlando, Florida, habits, and personal lifestyle. The dose for the 1985. average American is about 10 mrem per year from consumer products. • National Research Council, Committee on the Biological Effects of Ionizing Radia- ➤ Other Sources tion, Health Effects of Exposure to Low This category includes the generation of Levels of Ionizing Radiation, BEIR V, electricity from both coal and nuclear power National Academy Press, Washington, D.C., plants, the transportation of nuclear materi- 1990. als, and the storage of nuclear wastes. It also • James E. Turner, Atoms, Radiation and includes the exposures from fallout from the Radiation Protection, 2nd Edition, John international nuclear weapons testing Wiley & Sons, Inc., 1995 programs. These sources make up less than • Other Fact Sheets: one percent of the annual radiation exposure #1. What is Radioactive Material? — less than 3 mrem — to the average #2. What is Ionizing Radiation? American. This series of data sheets is based upon copyright material prepared by Ohio State University Extension under a grant from the Midwest Compact Commission. The material was reviewed and updated at Rutgers University, Department of Environmental Sciences by Alan Appleby, Ph.D., Martin Costello, M.S. and Steven Rose, M.S. Permission to use this material is gratefully acknowledged. November 1996.