Introduction To Radiation - Nuclear Safety
Introduction to RadiationDecember 2012
Introduction to Radiation Minister of Public Works and Government Services Canada (PWGSC) 2012PWGSC catalogue number CC172-93/2012E-PDFISBN 978-1-100-21572-3Published by the Canadian Nuclear Safety Commission (CNSC)Extracts from this document may be reproduced for individual use without permission providedthe source is fully acknowledged. However, reproduction in whole or in part for purposes ofresale or redistribution requires prior written permission from the Canadian Nuclear SafetyCommission.Également publié en français sous le titre de : Introduction au rayonnementDocument availabilityThis document can be viewed on the CNSC Web site at nuclearsafety.gc.caTo order a printed copy of the document in English or French, please contact:Canadian Nuclear Safety Commission280 Slater StreetP.O. Box 1046, Station BOttawa, Ontario K1P 5S9CANADATel.: 613-995-5894 or 1-800-668-5284 (in Canada only)Facsimile: 613-995-5086Email: info@cnsc-ccsn.gc.caWeb site: nuclearsafety.gc.ca
Introduction to RadiationDecember 2012
December 2012Table of Contents1.Overview. 12.Introduction to Radiation. 23.4.5.2.1Atoms: Where all matter begins . 22.2Isotopes . 32.3Radioisotopes. 4Types and Sources of Radiation . 63.1Non-ionizing radiation . 63.2Ionizing radiation. 63.3Natural sources of ionizing radiation. 83.4Artificial (man-made) sources of ionizing radiation. 103.5Striking a balance. 12Health Effects of Radiation Exposure . 134.1Epidemiological evidence. 134.2Cancer risk assessment . 144.3How radiation affects cells. 15Radiation Doses . 185.1Absorbed dose. 185.2Equivalent dose. 185.3Effective dose . 195.4Typical radiation doses . 195.56.7.5.4.1Natural radiation . 195.4.2Man-made sources . 21Dose Limits. 22Regulating Radiation . 256.1Protecting Canadians . 256.2Protecting workers . 26Summary . 28Glossary . 29Acronyms and Units . 36Sources . 36i
December 2012List of TablesTable 1: Potassium-40 content of certain foods. 10Table 2: Radioactive isotopes found in the human body (70 kg adult) . 10Table 3: Radiation doses, dose limits and potential health effects . 17Table 4: Average effective dose in select Canadian cities compared to worldwide average . 21Table 5: Typical equivalent doses from various radiological examinations. 22Table 6: Maximum effective annual doses to members of the public by year, from airborneand waterborne emissions . 24List of FiguresFigure 1: The electromagnetic spectrum. 1Figure 2: Model of an atom . 2Figure 3: The periodic table of elements . 3Figure 4: Radioactive decay curve of carbon-14 . 5Figure 5: Penetration abilities of different types of ionizing radiation. 7Figure 6: Sources of natural radiation. 8Figure 7: A gamma camera used in nuclear medicine, for diagnosing illnesses . 11Figure 8: A portable nuclear gauge. 11Figure 9: McClean Lake Uranium Mine (Saskatchewan) . 12Figure 10: Models to estimate the health risks from exposure to low levels ofionizing radiation . 15Figure 11: A strand of DNA . 16Figure 12: Relationship between effective, equivalent and absorbed doses. 18Figure 13: Tissue weighting factors. 19Figure 14: Annual outdoor effective dose from cosmic radiation for North America(in microsieverts) . 20Figure 15: Doses from natural background radiation in Canada . 21Figure 16: Radiation dose limitation framework . 23Figure 17: Canadian occupational dose by facility type for 2007 . 23ii
December 2012Introduction to Radiation1.OverviewRadiation is energy in the form of waves or streams of particles. There are many kinds of radiation allaround us. When people hear the word radiation, they often think of atomic energy, nuclear power andradioactivity, but radiation has many other forms. Sound and visible light are familiar forms of radiation;other types include ultraviolet radiation (that produces a suntan), infrared radiation (a form of heatenergy), and radio and television signals. Figure 1 presents an overview of the electromagnetic spectrum;section 3 will go into greater detail on the different types of radiation.Figure 1: The electromagnetic spectrum Reproduced by permission of World Nuclear Association, London, UK.Uncontrolled use of man-made radiation carries a potential risk to the health and safety of workers andthe public. This is where the Canadian Nuclear Safety Commission (CNSC) comes in. The CNSCregulates the use of nuclear energy and materials to protect the health, safety and security of Canadiansand the environment from the effects of radiation.The purpose of this document is to provide clear and simple information about radiation: what it is, whereit comes from and how it is used. It also presents information on radiation health effects, radiation dosesand how the CNSC ensures the safety of the Canadian nuclear sector through its comprehensiveregulatory framework and vigilant oversight.1
December 20122.Introduction to RadiationAll life has evolved in an environment filled with radiation. The forces at work in radiation are revealedupon examining the structure of atoms. Atoms are a million times thinner than a single strand of humanhair, and are composed of even smaller particles – some of which are electrically charged. Sections 2.1 to2.3 discuss atoms in more detail, along with basic radiation-related principles.2.1Atoms: Where all matter beginsAtoms form the basic building blocks of all matter. In other words, all matter in the world begins withatoms – they are elements like oxygen, hydrogen, and carbon.An atom consists of a nucleus – made up of protons and neutrons that are kept together by nuclear forces– and electrons that are in orbit around the nucleus (see Figure 2). The nucleus carries a positive charge;protons are positively charged, and neutrons do not carry a charge. The electrons, which carry a negativecharge, move around the nucleus in clouds (or shells). The negative electrons are attracted to the positivenucleus because of the electrical force. This is how the atom stays together.Figure 2: Model of an atomEach element is distinguished by the number of protons in its nucleus. This number, which is unique toeach element, is called the “atomic number”. For example, carbon has six protons; therefore, its atomicnumber is 6 on the periodic table (see Figure 3). In an atom of neutral charge, the atomic number is alsoequal to the number of electrons. An atom’s chemical properties are determined by the number ofelectrons, which is normally equal to the atomic number.2
December 2012Figure 3: The periodic table of elementsAtoms from one or more elements combine to form molecules. A molecule of water, for example, isformed of two atoms of hydrogen bound to one atom of oxygen (H2O).A nuclide is a specific type of atom characterized by the number of protons and neutrons in its nucleus,which approximates the mass of the nuclide. The number that is sometimes given with the name of thenuclide is called its mass number (the total number of protons and neutrons in the nucleus). For example,a nuclide of carbon with 6 protons and 6 neutrons is called carbon-12.2.2IsotopesAn isotope is a variant of a particular chemical element. While all isotopes of a given element have thesame number of protons, each isotope has a different number of neutrons.For example, hydrogen has three isotopes (or variants): hydrogen-1 (contains one proton and no neutrons) hydrogen-2, which is called deuterium (contains one proton and one neutron) hydrogen-3, which is called tritium (contains one proton and two neutrons)Another example is uranium-235, which has 92 protons and 143 neutrons, as opposed to uranium-238,which has 92 protons and 146 neutrons.3
December 2012An isotope is stable when it has a balanced number of neutrons and protons. In general, when an isotopeis small and stable, it contains close to an equal number of protons and neutrons. Isotopes that are largerand stable have slightly more neutrons than protons. Examples of stable nuclides include carbon-12 (sixprotons and six neutrons for a total mass of 12), phosphorus-30 (15 protons and 15 neutrons) and sodium 22 (11 protons and 11 neutrons).2.3RadioisotopesIsotopes that are not stable and emit radiation are called radioisotopes. A radioisotope is an isotope of anelement that undergoes spontaneous decay and emits radiation as it decays. During the decay process, itbecomes less radioactive over time, eventually becoming stable.Once an atom reaches a stable configuration, it no longer gives off radiation. For this reason, radioactivesources – or sources that spontaneously emit energy in the form of ionizing radiation as a result of thedecay of an unstable atom – become weaker with time. As more and more of the source’s unstable atomsbecome stable, less radiation is produced and the activity of the material decreases over time to zero.The time it takes for a radioisotope to decay to half of its starting activity is called the radiological halflife, which is denoted by the symbol t½. Each radioisotope has a unique half-life, and it can range from afraction of a second to billions of years. For example, iodine-131 has an eight-day half-life, whereasplutonium-239 has a half-life of 24,000 years. A radioisotope with a short half-life is more radioactivethan a radioisotope with a long half-life, and therefore will give off more radiation during a given timeperiod.There are three main types of radioactive decay: Alpha decay: Alpha decay occurs when the atom ejects a particle from the nucleus, which consists oftwo neutrons and two protons. When this happens, the atomic number decreases by 2 and the massdecreases by 4. Examples of alpha emitters include radium, radon, uranium and thorium. Beta decay: In basic beta decay, a neutron is turned into a proton and an electron is emitted from thenucleus. The atomic number increases by one, but the mass only decreases slightly. Examples of purebeta emitters include strontium-90, carbon-14, tritium and sulphur-35. Gamma decay: Gamma decay takes place when there is residual energy in the nucleus followingalpha or beta decay, or after neutron capture (a type of nuclear reaction) in a nuclear reactor. Theresidual energy is released as a photon of gamma radiation. Gamma decay generally does not affectthe mass or atomic number of a radioisotope. Examples of gamma emitters include iodine-131,cesium-137, cobalt-60, radium-226 and technetium-99m.The number of nuclear disintegrations in a radioactive material per unit time is called the activity. Theactivity is used as a measure of the amount of a radionuclide, and it is measured in becquerels (Bq).1 Bq 1 disintegration per second.If the original source of the radioactivity is known, it can be predicted how long it will take to decay to agiven activity. The decay is exponential and the isotope must go through many half-lives to become non radioactive. Figure 4 depicts the radioactive decay curve of carbon-14, which has a half-life of about5,700 years.4
December 2012Even after a radioisotope with a high activity has decayed for several half-lives, the level of remainingradioactivity is not necessarily safe. Measurements of a radioactive material’s activity are always neededto estimate potential radiation doses.Figure 4: Radioactive decay curve of carbon-145
December 20123.Types and Sources of RadiationRadiation is energy in the form of waves of particles. There are two forms of radiation – non-ionizing andionizing – which will be discussed in sections 3.1 and 3.2, respectively.3.1Non-ionizing radiationNon-ionizing radiation has less energy than ionizing radiation; it does not possess enough energy toproduce ions. Examples of non-ionizing radiation are visible light, infrared, radio waves, microwaves, andsunlight.Global positioning systems, cellular telephones, television stations, FM and AM radio, baby monitors,cordless phones, garage-door openers, and ham radios use non-ionizing radiation. Other forms include theearth’s magnetic field, as well as magnetic field exposure from proximity to transmission lines, householdwiring and electric appliances. These are defined as extremely low-frequency (ELF) waves and are notconsidered to pose a health risk.3.2Ionizing radiationIonizing radiation is capable of knocking electrons out of their orbits around atoms, upsetting theelectron/proton balance and giving the atom a positive charge. Electrically charged molecules and atomsare called ions. Ionizing radiation includes the radiation that comes from both natural and man-maderadioactive materials.There are several types of ionizing radiation:Alpha radiation (α)Alpha radiation consists of alpha particles that are made up of two protons and two neutrons each and thatcarry a double positive charge. Due to their relatively large mass and charge, they have an extremelylimited ability to penetrate matter. Alpha radiation can be stopped by a piece of paper or the dead outerlayer of the skin. Consequently, alpha radiation from nuclear substances outside the body does not presenta radiation hazard. However, when alpha-radiation-emitting nuclear substances are taken into the body(for example, by breathing them in or by ingesting them), the energy of the alpha radiation is completelyabsorbed into bodily tissues. For this reason, alpha radiation is only an internal hazard. An example of anuclear substance that undergoes alpha decay is radon-222, which decays to polonium-218.Beta radiation (β)Beta radiation consists of charged particles that are ejected from an atom’s nucleus and that are physicallyidentical to electrons. Beta particles generally have a negative charge, are very small and can penetratemore deeply than alpha particles. However, most beta radiation can be stopped by small amounts ofshielding, such as sheets of plastic, glass or metal. When the source of radiation is outside the body, betaradiation with sufficient energy can penetrate the body’s dead outer layer of skin and deposit its energywithin active skin cells. However, beta radiation is very limited in its ability to penetrate to deeper tissuesand organs in the body. Beta-radiation-emitting nuclear substances can also be hazardous if taken into thebody. An example of a nuclear substance that undergoes beta emission is tritium (hydrogen-3), whichdecays to helium-3.6
December 2012Photon radiation (gamma [γ] and X-ray)Photon radiation is electromagnetic radiation. There are two types of photon radiation of interest for thepurpose of this document: gamma (γ) and X-ray. Gamma radiation consists of photons that originate fromwithin the nucleus, and X-ray radiation consists of photons that originate from outside the nucleus, andare typically lower in energy than gamma radiation.Photon radiation can penetrate very deeply and sometimes can only be reduced in intensity by materialsthat are quite dense, such as lead or steel. In general, photon radiation can travel much greater distancesthan alpha or beta radiation, and it can penetrate bodily tissues and organs when the radiation source isoutside the body. Photon radiation can also be hazardous if photon-emitting nuclear substances are takeninto the body. An example of a nuclear substance that undergoes photon emission is cobalt-60, whichdecays to nickel-60.Neutron radiation (n)Apart from cosmic radiation, spontaneous fission is the only natural source of neutrons (n). A commonsource of neutrons is the nuclear reactor, in which the splitting of a uranium or plutonium nucleus isaccompanied by the emission of neutrons. The neutrons emitted from one fission event can strike thenucleus of an adjacent atom and cause another fission event, inducing a chain reaction. The production ofnuclear power is based upon this principle. All other sources of neutrons depend on reactions where anucleus is bombarded with a certain type of radiation (such as photon radiation or alpha radiation), andwhere the resulting effect on the nucleus is the emission of a neutron. Neutrons are able to penetratetissues and organs of the human body when the radiation source is outside the body. Neutrons can also behazardous if neutron-emitting nuclear substances are deposited inside the body. Neutron radiation is bestshielded or absorbed by materials that contain hydrogen atoms, such as paraffin wax and plastics. This isbecause neutrons and hydrogen atoms have similar atomic weights and readily undergo collisionsbetween each other.Figure 5 summarizes the types of radiation discussed in this document, from higher-energy ionizingradiation to lower-energy non-ionizing radiation. Each radiation source differs in its ability to penetratevarious materials, such as paper, skin, lead and water.Figure 5: Penetration abilities of different types of ionizing radiation7
December 20123.3Natural sources of ionizing radiationRadiation has always been present and is all around us in many forms (see Figure 6). Life has evolved ina world with significant levels of ionizing radiation, and our bodies have adapted to it.Many radioisotopes are naturally occurring, and originated during the formation of the solar system andthrough the interaction of cosmic rays with molecules in the atmosphere. Tritium is an example of aradioisotope formed by cosmic rays’ interaction with atmospheric molecules. Some radioisotopes (such asuranium and thorium) that were formed when our solar system was created have half-lives of billions ofyears, and are still present in our environment. Background radiation is the ionizing radiation constantlypresent in the natural environment.Figure 6: Sources of natural radiationThe United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) identifies fourmajor sources of public exposure to natural radiation: Cosmic radiationTerrestrial radiationInhalationIngestion8
December 2012Exposure from cosmic radiationThe earth’s outer atmosphere is continually bombarded by cosmic radiation. Usually, cosmic radiationconsists of fast moving particles that exist in space and originate from a variety of sources, including thesun and other celestial events in the universe. Cosmic rays are mostly protons but can be other particles orwave energy. Some ionizing radiation will penetrate the earth’s atmosphere and become absorbed byhumans which results in natural radiation exposure.Exposure from terrestrial radiationThe composition of the earth’s crust is a major source of natural radiation. The main contributors arenatural deposits of uranium, potassium and thorium which, in the process of natural decay, will releasesmall amounts of ionizing radiation. Uranium and thorium are found essentially everywhere. Traces ofthese minerals are also found in building materials so exposure to natural radiation can occur fromindoors as well as outdoors.Exposure through inhalationMost of the variation in exposure to natural radiation results from inhalation of radioactive gases that areproduced by radioactive minerals found in soil and bedrock. Radon is an odourless and colourlessradioactive gas that is produced by the decay of uranium. Thoron is a radioactive gas produced by thedecay of thorium. Radon and thoron levels vary considerably by location depending on the compositionof soil and bedrock.Once released into the air, these gases will normally dilute to harmless levels in the atmosphere butsometimes they become trapped and accumulate inside buildings and are inhaled by occupants. Radon gasposes a health risk not only to uranium miners, but also to homeowners if it is left to collect in the home.On average, it is the largest source of natural radiation exposure. For more information on radon, read theCNSC’s Radon and Health document (INFO-0813) at nuclearsafety.gc.ca or visit Health Canada's Website (hc-sc.gc.ca) to learn more about the means to control it in your home.Exposure through ingestionTrace amounts of radioactive minerals are naturally found in the contents of food and drinking water. Forinstance, vegetables are typically cultivated in soil and ground water which contains radioactive minerals.Once ingested, these minerals result in internal exposure to natural radiation.Naturally occurring radioactive isotopes, such as potassium-40 and carbon-14, have the same chemicaland biological properties as their non-radioactive isotopes. These radioactive and non-radioactiveelements are used in building and maintaining our bodies.Natural radioisotopes continually expose us to radiation and are commonly found in many foods, such asBrazil nuts. Table 1 identifies the amount of radioactivity from potassium-40 contained in about 500grams of different food products.9
December 2012Table 1: Potassium-40 content of certain foodsFoodRed meatWhite potatoCarrotBananaLima beansBrazil nuts1Activity in Bq per 500 grams5663636586103Source: Brodsky, 1978.1Brazil nuts also naturally contain radium-226 (between 19 and 130 Bq per 500 grams).Several radioactive isotopes also occur naturally in the human body (see Table 2).Table 2: Radioactive isotopes found in the human body (70 kg adult)IsotopesAmount of radioactivity in umTritiumUranium3,700 a40 b,d4,000 b1.1 b0.21 b23 c2.3 a, b, da ICRP, 1975b Eisenbud and Gesell, 1997c UNSCEAR, 2000d ICRP, 19803.4Artificial (man-made) sources of ionizing radiationPeople are also exposed to man-made radiation from medical treatments and activities involvingradioactive material. Radioisotopes are produced as a by-product of the operation of nuclear reactors, andby radioisotope generators like cyclotrons. Many man-made radioisotopes are used in the fields of nuclearmedicine, biochemistry, the manufacturing industry and agriculture. The following are the most commonsources: Medical sources: Radiation has many uses in medicine. The best-known application is in X-raymachines, which use radiation to find broken bones or to diagnose diseases. X-ray machines areregulated by Health Canada and provincial authorities. Another example is nuclear medicine, whichuses radioactive isotopes to diagnose and treat diseases such as cancer. A gamma camera (see Figure7) is one piece of medical equipment commonly used in diagnosis .The CNSC regulates theseapplications of nuclear medicine, as well as related equipment. It also licenses reactors and particleaccelerators that produce isotopes destined for medical and industrial applications.10
December 2012Figure 7: A gamma camera used in nuclear medicine, for diagnosing illnesses Industrial sources: Radiation has various industrial uses, which range from nuclear gauges (seeFigure 8) used in the building of roads to density gauges that measure the flow of material throughpipes in factories. Radioactive materials are also used in smoke detectors and some glow-in-the darkexit signs, as well as to estimate reserves in oil fields. Other applications include sterilization, whichis performed using large, heavily shielded irradiators. Industrial activities are licensed by the CNSC.Figure 8: A portable nuclear gauge Nuclear fuel cycle: Nuclear power plants (NPPs) use uranium to produce a chain reaction thatproduces steam, which in turn drives turbines to produce electricity. As part of their normal activities,NPPs release small quantities of radioactive material in a controlled manner to the surroundingenvironment. These releases are regulated to ensure doses to the public are well below regulatorylimits. Uranium mines (see Figure 9), fuel fabrication plants and radioactive waste facilities are alsolicensed so the radioactivity they release (that can contribute to public dose) can be controlled by theCNSC.11
December 2012Figure 9: McClean Lake Uranium Mine (Saskatchewan) 3.5Atmospheric testing: The atmospheric testing of atomic weapons from the end of the Second WorldWar until as late as 1980 released radioactive material, called fallout, into the air. As the falloutsettled to the ground, it was incorporated into the environment. Much of the fallout had short halflives and no longer exists, but some continues to decay. People and the environment receive smallerand smaller doses from the fallout every year.Striking a balanceNormally, there is little we can do to change or reduce ionizing radiation that comes from natural sourceslike the sun, soil or rocks. This kind of exposure, while never entirely free of risk, is generally quite low.However, in some cases, natural sources of radioactivity – such as radon gas in the home – may beunacceptably high and need to be reduced.The ionizing radiation that comes from man-made sources and activities is controlled more carefully. Inthese settings, a balance is struck between radiation’s societal benefits and the risks it poses to people,health and the environment. Dose limits are set to restrict radiation exposures to both workers andmembers of the public. In addition, licensees are required to keep all radiation doses as low as reasonablyachievable (ALARA). There must also be a net benefit to support the use of radiation. For example,smoke detectors are permitted to use radioactive isotopes because smoke detectors save lives. Similarly,nuclear power plants provide us with electricity, wh
Radiation is energy in the form of waves or streams of particles. There are many kinds of radiation all around us. When people hear the word radiation, they often think of atomic energy, nuclear power and radioactivity, but radiation has many other forms. Sound and visibl
NUCI 511 NUCLEAR ENGINEERING I Atomic and nuclear physics, interaction of radiation with matter, nuclear reactors and nuclear power, neutron diffusion and moderation, nuclear reactor theory, the time dependent reactor, heat removal from nuclear reactors, radiation protection, radiation
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Non-Ionizing Radiation Non-ionizing radiation includes both low frequency radiation and moderately high frequency radiation, including radio waves, microwaves and infrared radiation, visible light, and lower frequency ultraviolet radiation. Non-ionizing radiation has enough energy to move around the atoms in a molecule or cause them to vibrate .
Medical X-rays or radiation therapy for cancer. Ultraviolet radiation from the sun. These are just a few examples of radiation, its sources, and uses. Radiation is part of our lives. Natural radiation is all around us and manmade radiation ben-efits our daily lives in many ways. Yet radiation is complex and often not well understood.
Guide for Nuclear Medicine NUCLEAR REGULATORY COMMISSION REGULATION OF NUCLEAR MEDICINE. Jeffry A. Siegel, PhD Society of Nuclear Medicine 1850 Samuel Morse Drive Reston, Virginia 20190 www.snm.org Diagnostic Nuclear Medicine Guide for NUCLEAR REGULATORY COMMISSION REGULATION OF NUCLEAR MEDICINE. Abstract This reference manual is designed to assist nuclear medicine professionals in .
The Assistant Radiation Safety Officer (ARSO) assists the RSO in the management of the Radiation Protection Program. Radiation Safety Committee: The Radiation Safety Committee (RSC) is a body consisting of the RSO, ARSO, Executive Manager and persons trained and experienced in the safe use of radioactive materials and radiation producing devices.
Ionizing radiation: Ionizing radiation is the highenergy radiation that - causes most of the concerns about radiation exposure during military service. Ionizing radiation contains enough energy to remove an electron (ionize) from an atom or molecule and to damage DNA in cells.
Am I My Brother's Keeper? is a project by British artist Kate Daudy, who has transformed a large UNHCR tent; previously home to a Syrian refugee family in Jordan’s Za’atari camp into a participatory art installation focussing on the concepts of home and identity. During the year and a half she spent researching the project, Daudy visited refugee camps in Jordan. There and across Europe and .
