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Making Sense of Radiation Safety

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Making Sense of Radiation Safety MAKING SENSE OF Division of Radiation, Transport and Waste Safety, Department of Nuclear Safety and Security Vienna International Centre, PO Box 100, 1400 Vienna, Austria RADIATION SAFETY http://www-ns.iaea.org | [email protected] 16-3438 Protecting people and the environment NOTE FROM THE DIRECTOR The IAEA’s principal safety objective is to protect people and the environment from the harmful effects of ionizing radiation. This objective needs to be achieved without unduly restricting the many beneficial uses of radiation enjoyed by society. The IAEA recognizes that the principles of radiation safety, which involve various scientific disciplines such as nuclear physics, molecular biology, epidemiology and medicine, need thorough explanation. When setting standards of protection and safety, it is also important to take into account and apply ethical considerations. States and provision for their application in States are a top priority for the IAEA. In the Radiation sources provide many beneficial process of developing standards, all IAEA applications for medicine, industry and Member States are invited to participate such research, and their uses continue to increase. that a broad international consensus on their These man-made sources of radiation are in content is achieved. addition to natural radiation sources. While for most people natural sources of radiation Many States have adopted these standards dominate their exposure, man-made sources into national legislation and regulations. tend to be more controllable. While we In addition, the IAEA works with other cannot entirely avoid radiation exposure, in international bodies with responsibilities situations where it is controllable we may need for radiation safety to ensure the widest to consider actions to protect people and the acceptance and application of these standards. environment. In the management of radiation exposure, it is important to ensure that the Against this background, I am pleased to appropriate balance is maintained between introduce this booklet on radiation safety. This the risks posed and the benefits derived by booklet discusses levels of radiation exposure both individuals and society in general. from both artificial and natural sources, the risks that they pose and the overall approach In developing an appropriate approach to to their control. It also describes the process radiation safety, the first step is to understand by which the IAEA develops radiation safety the magnitude of the doses and the risks standards. I hope that through this booklet, associated with the various sources of ionizing readers will gain a better understanding of radiation that we are exposed to throughout the science and philosophy that underpins our our lives. The next step is to determine what work. exposures are controllable and how they should be controlled. Peter Johnston, Director By statute, the IAEA is required to establish Division of Radiation, “standards of safety for protection of Transport and Waste Safety health and minimization of danger to life and property” and to “provide for their application”. The establishment of radiation safety standards that are applicable in all MAKING SENSE OF RADIATION SAFETY 2 WHAT ARE THE MOST COMMONLY ENCOUNTERED RADIONUCLIDES? Radionuclides may be divided into two broad classes—those that occur naturally and those that have been produced artificially, for example in a nuclear reactor or accelerator. INTRODUCTION NATURALLY OCCURRING RADIONUCLIDES Some radionuclides have been naturally present in the environment since the Earth was formed and their half-lives (the time it takes for the activity of a given quantity of COSMIC RAYS radioactive material to reduce to a half) are WHAT IS RADIATION? These are a complex mixture of many dif- comparable with the age of the Earth. The ferent types of ionizing radiation (protons, main naturally occurring radionuclides in the Radiation is energy in the form of electro- neutrons, alpha particles, electrons and environment are listed in Table 1. magnetic waves (photons) or subatomic other high-energy particles). They come particles. It is generally classified as either from deep space, mostly outside the solar These radionuclides are present throughout ionizing or non-ionizing according to system. the Earth’s crust in varying amounts and, whether its energy is high enough to ionize over time, transform into stable nuclides. As the matter through which is passes. The RADIOACTIVE MATERIALS part of this process, everyone is exposed to IAEA is only concerned with safety relating Some atoms (isotopes) of some chemi- radiation from them, but the levels of expo- to exposure to ionizing radiation—X-rays, cal elements are unstable and transform sure vary widely. gamma rays, alpha particles, beta particles themselves into atoms (isotopes) of other and neutrons. elements by emitting radiation. This trans- Additionally, there are radionuclides present formation process is called “radioactivity”. throughout the environment produced by the The isotopes of an element that exhibit this interaction of cosmic rays with the Earth’s property are said to be “radioactive” and atmosphere. These comprise mainly hydro- Naturally occurring radionuclides are found in varying are called “radionuclides”. The radiation gen-3 (tritium) and carbon-14. concentrations in the Earth’s crust. WHERE DOES IONIZING emitted during the transformation process RADIATION COME FROM? can be in the form of particles (electrons, neutrons and alpha particles) or photons There are three main sources of ionizing (X-rays and gamma rays). radiation: high-voltage machines, cosmic rays and radioactive materials. Table 1. Main naturally occurring radionuclides in the environment HIGH-VOLTAGE MACHINES The most common high-voltage machines are X-ray machines, such as those used in • Isotopes of uranium (mainly uranium-238, but also uranium-235 medicine. Here, the X-rays are produced and uranium-234) and their radioactive progeny (such as in a vacuum by bombarding a target made Some atoms of some radium-226, radon-222 and polonium-210); of a material such as tungsten with an chemical elements are electron beam. The older generation of • Isotopes of thorium (mainly thorium-232, but also thorium-230 television sets and electronic valves also unstable and transform and thorium-228,) and their radioactive progeny (such as produced small amounts X-rays. themselves into atoms radon-220); and of other elements by • Potassium-40, the one naturally occurring radioactive isotope of FIGURES & FACTS potassium. Potassium contains 120 parts per million (0.012%) of emitting radiation. This potassium-40. transformation process is called radioactivity. 3 MAKING SENSE OF RADIATION SAFETY 4 ARTIFICIALLY PRODUCED RADIONUCLIDES Ban Treaty came into effect, which prohibited Table 3. Significant environmental releases of iodine-131 and caesium-137 Since the 1950s, a wide range of artificially nuclear weapons tests in the atmosphere, produced radionuclides has become available. outer space and underwater. Additionally, Some of these are used worldwide for a vari- accidents in nuclear facilities at Chernobyl in Iodine-131 (PBq) Caesium-137 (PBq) ety of peaceful purposes in industry, medi- 1986 and at Fukushima in 2011 have also led cine, education and research (see Table 2). to large releases of radioactive material to the environment (see Table 3)[1,2]. Nuclear weapons Many of the radionuclides used in medi- 675,000 948 tests [1] cine and industry are in the form of sealed sources—that is, the radioactive material is sealed within an impervious capsule or hous- Chernobyl NPP 1,760 85 ing that has sufficient mechanical strength accident [1] to prevent contact with and dispersion of the radioactive material it contains. However, Fukushima NPP some radionuclides have to be used in an ~125 ~ 92 unsealed form, for example in nuclear medi- accident [2] cine. Facilities that use or handle radioactive material in unsealed form—such as some hos- Note: PBq stands for peta-becquerel (i.e. 1015 Bq). The becquerel is the unit of activity of a pitals and plants that process spent nuclear radionuclide; one becquerel corresponds to one disintegration per second [1,2]. fuel—may discharge some radionuclides to the environment in the course of normal opera- tions. These discharges are strictly regulated and must follow specific safety requirements, limitations and conditions related to exposure Consequently, there has been some addition of artificially produced radionuclides to the of members of the public and protection of already existing levels of naturally occurring radionuclides in the environment and, as a the environment. result, some additional radiation exposure of people. During the 1950s and the first half of the 1960s, large amounts of radionuclides were released to the general environment during WHY DO NUCLEAR REACTORS the testing of nuclear weapons, particularly neutron CONTAIN LARGE AMOUNTS OF when such testing was undertaken in the Artificially produced radionuclides are widely used in atmosphere. In 1963, the Partial Nuclear Test laboratory experiments. RADIOACTIVE MATERIAL? RADIATION WEIGHTING FACTORS, wR Most nuclear reactors use uranium, specif- ically, the isotope uranium-235, as the fuel target for producing energy. Energy is released Table 2. Some uses of artificially produced radionuclides when the nucleus of uranium-235 is bom- nucleus barded by neutrons and “splits” into smaller parts—this process is referred to as “nuclear fission” (see Figure 1). While Industrial
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