|Sources of Natural Radiation|
|Sources of Artificial Radiation|
|Biological Effects of
|International Standards for
|Application of the Basic Safety
Introduction to Radiation
Heat and light are types of radiation that people can feel or see, but there are other kinds of radiation that human senses cannot detect. Indeed, we constantly receive such invisible radiation from the sky, the ground, the air, and even our food and drink. Such "ionizing" radiation has been put to many uses: doctors use X rays to diagnose disease or injury; factories use radiation to check welds in machine components; gamma rays are used to sterilise medical equipment for safe use; and many new varieties of crops have been produced through radiation-induced mutations. Today, moreover, about 17 percent of the world's electricity is supplied by nuclear power plants.
The usefulness of radiation means that many people receive small doses of radiation from artificial sources as well as doses from nature. The IAEA has produced this booklet in order to enhance public understanding about the sources and effects of radiation, and to describe the measures that have been developed internationally to ensure the safe use of radiation.
Types of Radiation
"Ionizing" radiation passes through matter and can cause some of its atoms to become electrically charged, or ionized. In living tissues, the ions caused by such radiation can affect normal biological processes. Ionizing radiation comes in several different forms:
Alpha particles - are positively charged particles. They are easily stopped by paper or skin, and are only hazardous if alpha-emitting materials are swallowed or breathed into the body.
Beta particles - are electrons and have a greater penetrating power than alpha particles, but can be stopped by thin layers of water, glass or metal. However, beta emitting material can be hazardous if taken into the body.
Gamma and X rays - are electromagnetic radiations similar to light and radio waves but with shorter wavelengths. They are very penetrating and heavy shielding materials like lead and concrete are needed to stop them.
Neutrons - are particles with no charge; they are neutral, and because of this they can penetrate many materials very easily. They do not produce ionization directly, but their interaction with atoms can give rise to alpha, beta, gamma or X rays which produce ionization. Neutrons can only be stopped by thick masses of concrete, water or paraffin.
Ionizing radiation from radioactive materials diminishes over time at various rates as the atoms change into other atoms. Often, there is not just the disappearance of one kind of radiation, but the production of different radiations if the new atoms are radioactive. The time for half the radioactivity to dissipate is called the "half-life". Half-lives vary from a small fraction of a second to many millions of years.
The amount of radiation the `dose' received by people is measured in millisieverts (mSv). This unit belongs to the same family as the litre and kilogram, the most commonly accepted, international system of units.
Sources of Natural Radiation
Everyone is exposed to radiation, and for most people nature is the largest source of exposure.(see Fig.1)
Cosmic radiation comes through the earth's atmosphere, some from the sun and energy sources in our galaxy or outside it. Those from the sun are more intense during solar flares but the others are fairly constant in number. However, the density is affected by the earth's magnetic field, which makes it greater nearer the poles than the equator. The radiation dose people receive increases therefore with latitude. In addition, the earth's atmosphere is a partial shield to the radiation. As one goes higher there is a lower shielding effect and the dose increases as the altitude increases. Buildings and the fuselages of aircraft provide little protection.(see Fig.2) The global yearly average dose is 0.39 millisieverts.
The Earth's Crust is made up of materials that are naturally radioactive. Uranium, for instance, is dispersed throughout rocks and soil, mostly at very low concentrations. So are thorium and potassium-40. They nearly all emit gamma rays which irradiate the whole body more or less uniformly. Since building materials are extracted from the earth, they can be slightly radioactive, and people are irradiated indoors as well as out of doors. The radiation doses vary according to the rocks and soils of the area and the building materials in use but the global yearly average is 0.46 millisieverts.
Radon is a naturally radioactive gas that comes from the uranium that is widespread in the earth's crust. It is emitted from rocks or soil at the earth's surface and disperses in the atmosphere unless it enters a building, in which the concentration can build up. Radon decays to form other radioactive atoms which, when inhaled, can lodge in the lung and irradiate tissue. The global yearly average dose is 1.3 millisieverts but in high radon areas the doses can be many times higher. The radiation dose can most easily be reduced by preventing the radon gas from entering it in the first place.(see Fig.3)
Food and Drink. Since radioactive materials occur everywhere in nature it is inevitable that they get into drinking water and food, giving a global yearly average dose of 0.23 millisieverts. Potassium-40 in particular is a major source of internal irradiation, but there are others. Potassium-40 in the body varies with the amount of muscle, for instance, being twice as high in younger men than in older women. Some foods, for example shellfish and Brazil nuts, concentrate radioactive materials so that, even when there is no artificial radioactivity, people who consume large quantities can receive a radiation dose significantly above average.
Sources of Artificial Radiation
Doses from artificial radiation are, for most of the population, much smaller than those from natural radiation but they still vary considerably. They are in principle fully controllable, unlike natural sources.
Medical. Radiation is used in medicine in two distinct ways: to diagnose disease or injury; and to kill cancerous cells. In the oldest and most common diagnostic use, X rays are passed through the patient to produce an image. The technique is so valuable that millions of X ray examinations are conducted every year. One chest X ray will give 0.1 mSv of radiation dose. For some diseases, diagnostic information can be obtained using gamma rays emitted by radioactive materials introduced into the patient by injection, or by swallowing or by inhalation. This technique is called nuclear medicine. The radioactive material is part of a pharmaceutical chosen so that it preferentially locates in the organ or part of the body being studied. To follow the distribution or flow of the radioactive material a gamma camera is used. It detects the gamma radiation and produces an image, and this indicates whether the tissue is healthy or provides information on the nature and extent of the disease.
Cancerous conditions may be treated through radiotherapy, in which beams of high energy X rays or gamma rays from cobalt-60 or similar sources are used. They are carefully aimed to kill the diseased tissue, often from several different directions to reduce the dose to surrounding healthy tissue. Radioactive substances, either as small amounts of solid material temporarily inserted into tissues or as radioactive solutions, can also be used in treating diseases, delivering high but localised radiation doses.
Medical uses of radiation are by far the largest source of man-made exposure of the public; the global yearly average dose is 0.3 millisieverts.
Environmental Radiation. Radioactive materials are also present in the atmosphere as a result of atomic bomb testing and other activities. They may lead to human exposure by several pathways external irradiation from radioactive materials deposited on the ground; inhalation of airborne radioactivity, and ingestion of radioactive materials in food and water.
Radioactive fall-out from nuclear weapons tests carried out in the atmosphere is the most widespread environmental contaminant but doses to the public have declined from the relatively high values of the early 1960s to very low levels now. The global yearly average dose is 0.006 millisieverts. However, where tests were carried out at ground level or even underground, localised contamination often remains near weapons sites.
Nuclear and other industries, and to a small degree hospitals and universities, discharge radioactive materials to the environment. Nearly all countries regulate industrial discharges and require the more significant to be authorized and monitored. Monitoring of such effluent may be carried out by the government department that authorizes the discharges as well as by the operator.
The nuclear power industry releases small quantities of a wide variety of radioactive materials at each stage in the nuclear fuel cycle. For the public the global yearly average dose is 0.008 millisieverts. The type of radioactive materials, and whether they are liquid, gaseous or particulate depends upon the operation of each process. For instance, nuclear power stations release carbon-14 and sulphur-35, which find their way through food chains to humans. Liquid discharges include radioactive materials that people may ingest through fish and shellfish.
The yearly dose to individuals living close to a power plant is small - usually a fraction of a millisievert; doses to people further away are even smaller. Reprocessing nuclear fuel produces higher doses which vary greatly from plant to plant. For the most exposed members of the public, they can be as high as 0.4 millisieverts, but for most of the population they are very much smaller.
World-wide, there are estimated to be four million workers exposed to artificial radiation as a result of their work, with an average yearly dose of about 1 millisievert. Another five million (mostly in civil aviation) have yearly average doses due to natural radiation of 1.7 millisieverts.
Non-nuclear industries also produce radioactive discharges. They include the processing of ores containing radioactive materials as well as the element for which the ore is processed. Phosphorus ores, for instance, contain radium which can find its way into the effluent. A very different industry, the generation of electricity by coal-fired power stations, results in the release of naturally-occurring radioactive materials from the coal. These are discharged to air and transfer through food chains to the population. However, the radiation doses are always low - 0.001 millisieverts or less.
Accidental releases of radioactive materials. Apart from contamination due to the normal operations of the nuclear industry, radioactivity has been widely dispersed accidentally. The most significant accident was at Chernobyl nuclear power station in the Ukraine, where an explosion caused the release of large amounts of radioactivity over a period of several days. Airborne radioactive material dispersed widely over Europe and even further afield. Contamination at ground level varied considerably, being much heavier where rain washed the radioactivity out of the air. Radiation doses therefore varied significantly from normal. More than 100,000 people were evacuated during the first three weeks following the accident. Whole body doses received from external radiation from the Ukrainian part of the 30-km exclusion zone showed an average value of 15 millisieverts. (source OECD, 1995)
Radiation in Consumer Products. Minute radiation doses are received from the artificial radioactivity in consumer goods such as smoke detectors and luminous watches, and from the natural radioactivity of gas mantles. The global yearly average dose is extremely small (0.0005 millisieverts).
Biological Effects of Ionizing Radiation
The health effects of radiation may be divided into those that occur early and those that occur late.
Short term: It has long been recognized that exposure to high levels of radiation can harm exposed tissues of the human body. Such radiation effects can be clinically diagnosed in the exposed individual; they are called deterministic effects because once a radiation dose above the relevant threshold has been received, they will occur and the severity depends on the dose.
Long-term: Studies of populations exposed to radiation, especially of the survivors of the atomic bombing of Hiroshima and Nagasaki, have shown that exposure to radiation can also lead to the delayed induction of cancer and, possibly, of hereditary damage. Effects such as these cannot usually be confirmed in any particular individual exposed but can be inferred from statistical studies of large populations: they appear to occur at random in the irradiated population.
Information on the biological effects of ionizing radiation is assembled and published periodically by a number of expert bodies. The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) is an inter-governmental Committee made up of prominent scientists from many countries around the world and is charged with assembling, studying and disseminating information on the observed levels and the effects of ionizing radiation, both natural and man-made. The International Commission on Radiological Protection (ICRP) was established nearly 70 years ago, and is an independent, non-governmental group of experts whose recommedations are generally adopted as the basis for national regulations governing radiation exposure.
For radiation protection purposes, exposure to ionizing radiation is most often measured in terms of "effective dose." This is based on the energy deposited in tissue by radiation, taking into account the type of radiation and the sensitivity of the tissues irradiated. It is thus a measure of the overall risk arising from the exposure. The unit is the sievert, but millisieverts (mSv) are commonly used.
International Standards for Radiation Protection
To control the radiation exposure of workers, medical patients and the public, many countries have developed laws, which are supported by administrative measures and enforced by inspectors. Equally important is to have internationally agreed standards, and the International Atomic Energy Agency has played a lead role in developing and refining these. The IAEA together with the World Health Organization, International Labour Organisation, OECD Nuclear Energy Agency, Food and Agriculture Organization and Pan American Health Organization recently revised and updated its International Basic Safety Standards (BSS) for protection against ionizing radiation and the safety of radiation sources.
The new Standards are intended to ensure the safety of all types of radiation sources and to complement engineering safety standards developed for large and complex radiation sources, such as nuclear reactors and radioactive waste management facilities. The Standards are not mandatory, but can serve as a practical guide to all those involved in radiation protection, taking into account local situations, resources, etc. The BSS are enforced in all activities involving IAEA assistance and support.
A wealth of new information about radiation exposure over the past decade prompted the revision of the BSS. First and foremost, a study of the biological effects of radiation doses received by the survivors of the atomic bombing of Hiroshima and Nagasaki suggested that exposure to low-level radiation was more likely to cause harm than previously estimated. Other developments notably the nuclear accident at Three Mile Island in 1979 and that at Chernobyl in 1986, with its unprecedented transboundary contamination had a profound effect on the public perception of the potential danger from radiation exposure. There were serious accidents with radiation sources used in medicine and industry in Mexico, Brazil, El Salvador and other countries. In addition, more has been discovered about natural radiation such as household radon as a cause of concern for health. Finally, natural radiation exposures of workers such as miners, who were not thought of as radiation workers, were discovered to be much higher than had been realized.
Principles of radiation protection
The BSS apply to both "practices" and "interventions":
Practices are activities that add radiation exposure to that which people normally receive due to background radiation, or that increase the likelihood of incurring exposure. These include the use of radiation or radioactive substances for medical, industrial, agricultural, educational, training and research purposes and, of course, the generation of energy by nuclear power. Also included are facilities containing radioactive substances or devices such irradiation installations, mines and mills processing radioactive ores and radioactive waste management facilities.
Interventions are any activities that seek to reduce the existing radiation exposure, or the likelihood of incurring exposure. These apply to both chronic exposure situations such as radon in buildings, and emergency situations such as those created by contamination in the aftermath of an accident.
Protection under the BSS is based on the principles of the International Commission on Radiological Protection, which can be summed up as follows:
Justification of the practice. No practice involving exposure to radiation should be adopted unless it produces a benefit that outweighs the harm it causes or could cause.
Optimization of protection. Radiation doses and risks should be kept as low as reasonably achievable economic and social factors being taken into account; constraints should be applied to dose or risk to prevent an unfair distribution of exposure or risk.
Limitation of individual risk. Exposure of individuals should not exceed specified dose limits above which the dose or risk would be deemed unacceptable.
All three principles apply to the protection of workers and the public. However, to protect patients during the medical use of ionizing radiation only justification and optimization apply. Dose limits are not applicable to medical exposure, but guidance levels which show what is achievable by good practice may be established for use by medical practitioners. Dose limits are also inapplicable to interventions, which are concerned with reducing exposure.
|The dose limits for practices are intended to ensure that no individual is committed to unacceptable risk due to radiation exposure. For the public the limit is 1 mSv in a year, or in special circumstances up to 5 mSv in a single year provided that the average does over five consecutive years does not exceed 1 mSv per year|
The objective of the BSS is to prevent the occurrence of short term effects of high doses of radiation and to restrict the likelihood of occurrence of long term effects. Assuming that a practice is justified, the objective is achieved both by optimizing the protection of the exposed individuals and by ensuring the safety of the source of exposure.
For any justified interventions, the objective is achieved by keeping the individual doses lower than the threshold levels for deterministic effects and keeping all doses as low as reasonably achievable in the circumstances.
Justification of practices and interventions involves many factors, including social and political aspects, as well as radiological considerations. Some practical guidance on justification for practices and interventions is provided by the BSS, and some examples are provided here:
An intervention is justified if it is expected to achieve more good than harm, having regard to health, social and economic factors. Protective actions are nearly always justified if, in the absence of intervention, doses are expected to approach certain specified values related to deterministic effects.
Application of the Basic Safety Standards
The BSS set out detailed requirements for practices and interventions to protect workers, patients and the general public from radiation exposure. They also recommend procedures for ensuring the safety of sources, for accident prevention, for emergency planning and preparedness and for mitigating the consequences of accidents. Although the majority are of a qualitative nature, the BSS also establish many requirements expressed in terms of restrictions or guidance on the dose that may be incurred by people. The range of doses spreads over four orders of magnitude, from ones that are so minute that they should be exempt from the requirements to doses that are large enough to make intervention almost mandatory.
National governments usually have the responsibilities for enforcing radiation safety standards, generally through a system that includes a regulatory authority. In addition, governments usually provide for certain essential services for radiation protection and safety and for interventions that exceed or that complement the capabilities of regulators. The BSS can only be effectively applied when such a national infrastructure is firmly in place. In addition to legislation and regulations, the essential elements are:
A Regulatory Authority. This should be empowered to authorize and inspect, and to enforce the legislation and regulations. It must have sufficient resources, including adequate numbers of trained personnel. There must be arrangements for detecting any build up of radioactive substances in the general environment, for disposing of radioactive waste and preparing for interventions, particularly during emergencies, that could result in exposure of the public.
Education, training and public information. There must be adequate arrangements and resources for these, as well as for the exchange of information among specialists. There must also be appropriate means of informing the public, its representatives and the information media about health and safety concerns.
Facilities and services for radiation protection and safety must be well established at the national level. These include laboratories for personal dosimetry and environmental monitoring, and calibration and intercomparison of radiation measuring equipment; they could also include central registries for radiation dose records and information on equipment reliability.
To ensure radiation safety, the BSS promotes development of:
The BSS promotes sound technical planning and implementation through the following:
Security of sources. Radiation sources must be kept secure so as to prevent theft or damage.
Defence in depth. A multilayer system of protection and safety provisions commensurate with the radiation hazards involved is applied to sources, so that a failure at one layer is compensated for or corrected by subsequent layers.
Good engineering practice. This reflects approved codes and standards, and must be supported by reliable management and organization to ensure protection and safety throughout the life of the sources.
Verification of safety. Protection and safety measures for sources must be made in a way that they can be regularly monitored and verified for compliance. In addition, records should be kept of the results of monitoring and verification.
Additionally, radioactive substances have to be transported in accordance with the IAEA Regulations for the Safe Transport of Radioactive Material and with any applicable international convention.
|Under the BSS, interventions apply to the following:
|Exposure resulting from||Basis||Equivalent period of global exposure to average natural background|
|Nuclear weapons testing||All past tests||2- 3 years|
|Apparatus and substances used in medicine||One year of pracitce at the current rate||90 days|
|Severe accidents||Accidents to date||20 days|
|Nuclear power generation (under normal operating conditions)||Total nuclear generation to date. One year of practice at the current rate||1 day|
|Occupational activities||One year of occupational activities at the current rate||8 hours|
Most of the ionizing radiation that people are exposed to in day-to-day activities comes from natural, rather than manmade, sources. The health effects of radiation both natural and artificial are relatively well understood and can be effectively minimized through careful safety measures and practices. The IAEA, together with other international and expert organizations, is helping to promote and institute Basic Safety Standards on an international basis to ensure that radiation sources and radioactive materials are managed for both maximum safety and human benefit.
For further information please contact:
International Atomic Energy Agency
Division of Radiation and Waste Safety
Wagramerstr. 5, P.O.Box 100
A-1400 Vienna, Austria
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