Understanding Radiation In Our World - UMass Lowell

U N D E R S TA N D I N G R A D I AT I O N I N O U R WO R L DIIntroductionRadiation as a Part of OurEveryday LivesRadiation is all around us, every minute ofevery day. Some radiation is essential to life,such as heat and light from the sun. Wecould not exist without it. Some radiationinforms and entertains us, through videosignals and sounds from television sets andradios. As used in medicine, radiation helpsus diagnose and treat diseases and savelives. Yet it can also pose serious risks.Radiation is energy that comes from bothnatural sources, and manmade sources thatprovide many of the conveniences andnecessities of modern living.Natural RadiationWe are exposed to radiation from numerousnatural background sources: the atmosphere, soil and water, food, and even ourown bodies. On average, much more ofour exposure to radiation comes fromthese natural sources than from manmadesources.Manmade RadiationA smaller but increasing amount of theradiation we are exposed to is manmade.Modern technologies, for example, use radiation to: Diagnose and treat medical problems Communicate over long distances Generate electricity for our domestic andindustrial needs Conduct basic and applied researchDangers of RadiationManaging exposure to radiation is a majorconcern to citizens and government officials in the United States and around theworld.IntroductionDangers ofRadiation Excessive exposure to high-energy (ionizing) radiation can trigger changes inbody cells leading to cancer, birthdefects, and—in extreme cases—catastrophic illness and death. Too much exposure to the sun’s rays candamage eyes and burn skin, causingcataracts or cancer.Several events and circumstances continueto influence public perceptions about radiation dangers. Pictures and stories of the terrible effectsof massive radiation doses to the peopleof Hiroshima and Nagasaki have createda lasting fear of radiation. Development and testing of nuclearweapons have left a legacy of pollutionthat in the United States alone will takedecades and billions of dollars to cleanup. Accidents at two nuclear power plants—Three Mile Island in Pennsylvania andChernobyl in the former SovietUnion—introduced the term “meltdown” to popular culture and raised continuing questions about the safety ofnuclear power. Eliminate harmful bacteria from food9

U N D E R S TA N D I N G R A D I AT I O N I N O U R WO R L DIn addition, uncertainties remain about thesafe disposal of spent fuel from nuclearpower plants and other high-level radioactive waste.About this GuidebookThis guidebook provides information on: The nature and sources of radiation Benefits and risks involved in use ofradiation1 Management of radioactive wasteIntroduction Actions by state, federal, and internationAbout thisGuidebookal agencies and by individuals to ensurethat public health is protected from radiation hazardsThe goal of Understanding Radiation in OurWorld is to help you make informed judgments on important radiation issues thataffect your health, your lifestyle, and thewell-being of your family and community: How big a risk does radiation pose to us,our families, children, future generations,and the environment? How much and what kinds of risk shouldwe tolerate? What should we do, as individuals and asa society, to ensure that the benefits ofradiation are not outweighed by the risks?10

U N D E R S TA N D I N G R A D I AT I O N I N O U R WO R L D1What is the Nature of Radiation?EnergyRadiation is energy—the primal energy ofthe universe, originally created billions ofyears ago. Ionizing radiation is emitted asthe unstable atoms of radioactive materialsconstantly emit alpha, beta, gamma, orother forms of radiation as they “decay” to astable state. This process can take from afraction of a second to billions of years,depending on the material. Radioactivematerials (called radioisotopes or radionuclides) and the radiation they produce areeverywhere—in the soil, in our food andwater, and in our bodies.There is an important difference betweenradiation and radioactivity (although theterms are often mistakenly used interchangeably): Radiation is energy in the form of wavesor particles sent out over a distance. (Asimple example is the ripples of waterradiating outward in a pond after a pebbleis dropped into the water.) There aremany different types of radiation. Radioactivity is a property of a substance,such as uranium or plutonium, whichemits high-energy (ionizing) radiation.Radiation travels over distances rangingfrom fractions of a millimeter to billions oflight-years. This energetic quality of radiation makes life possible but also presentsthreats of danger and destruction.What is theNature ofRadiation?To better understand radiation it is important to remember that:Types ofRadiation Not all radiation is the same. Different kinds of radiation affect livingthings in different ways.Types of RadiationThe most basic distinction scientists makebetween types of radiation is the amount ofenergy involved (Figure 1). Radiation withlower energy levels is called nonionizing;radiation with higher energy levels is calledionizing.This guidebook sometimes uses the genericterm “radiation” to refer to ionizing radiation. Keep the differences between the twotypes in mind as you consider the benefitsand risks of the various types of radiation.Nonionizing RadiationNonionizing radiation has lower energy levels and longer wavelengths. ExamplesFigure 1.TheElectromagneticSpectrumSource:The Ohio StateUniversity Extension11

U N D E R S TA N D I N G R A D I AT I O N I N O U R WO R L DTable 1: Basic Types of RadiationTypeExamplesNon-Ionizing Electromagnetic RadiationRadio waves, Microwaves,Infrared (heat), Visible light (color)Ionizing Electromagnetic RadiationX-rays, Gamma rays, Cosmic raysIonizing Atomic Particle RadiationBeta radiation, Alpha radiation, Neutronsinclude radio waves, microwaves, visiblelight, and infrared rays from a heat lamp.1What istheNature ofRadiation?Structure ofAtomsOur senses can detect some types of nonionizing radiation: we can see visible light,and feel the burning effects of infraredradiation.Nonionizing radiation is strong enough toinfluence the atoms it contacts, but notstrong enough to affect their structure. Forexample, microwave radiation is used toheat the water in food by causing watermolecules to vibrate.Living tissue can generally be protectedfrom harmful nonionizing radiation bydevices such as goggles, protective clothing,and shielding around radiation-generatingequipment. However, concern has beenraised about possible health effects fromnonionizing radiation produced by suchthings as cell phones and electric powerlines. (See Electric and Magnetic Fields,Chapter 2, page 22)Ionizing RadiationIonizing radiation has higher energy levels.Examples include X-ray and cosmic rays.Ionizing radiation has enough energy todirectly affect the structure of atoms of thematerials, including human tissue, which itpasses through. A description of the structure of atoms will help in understanding theeffects of ionizing radiation. (Table 1)Structure of AtomsAll substances are composed of atoms thatare made up of three subatomic particles:protons, neutrons, and electrons except hydrogen (which may have no neutrons). Theprotons and neutrons are tightly boundtogether in the positively charged nucleusat the center of the atom, while a cloud ofnegatively charged electrons orbits thenucleus. (Figure 2)The number of protons in the nucleusdetermines its atomic element. The simplestelement, hydrogen, has only one proton inits nucleus. Oxygen has eight protons.Heavier elements, such as uranium and plutonium, have more than 90 protons.Elements may have various isotopes. AnFigure 2.Structure of an Atomnucleus:contains protons( )and neutronselectrons (-)12Source: U.S. Environmental Protection Agency

U N D E R S TA N D I N G R A D I AT I O N I N O U R WO R L Disotope is one of two or more atoms thathave the same number of protons but different numbers of neutrons in their nuclei.Most atoms are stable because the nuclearforces holding the protons and neutronstogether are strong enough to overcome theelectrical energy that tries to push the protons apart. (The energy pushing protonsapart is like two magnets with the samecharge that push each other apart.)When the number of neutrons in thenucleus is above a certain level, however,the atom becomes unstable or radioactive,and some of its excess energy begins toescape. This energy is ionizing radiation.Effects of Ionizing Radiation onAtomsWhen ionizing radiation passes throughmaterial, such as human tissue, it may“knock” one or more negatively chargedelectrons out of orbit around the nuclei ofatoms of the material. If this happens, thiscauses the atoms to become positivelycharged (ionized). When this occurs in ourbodies, molecules and cells may be damaged. The health effects of this damage maybe immediate or appear gradually overmany years.Detection of Ionizing RadiationIonizing radiation is generally notdetectable by our senses: we cannot see,smell, hear, or feel it. This, together with itsunpredictable health effects, may explainwhy it causes so much anxiety.However, ionizing radiation is relativelyeasy to detect and measure using electronicequipment. Instruments such as Geigercounters can detect radiation and help ustrack the amount of radiation exposure.These instruments can tell us if we are tooclose to a source that can harm us and warnus of a release of radiation.Radioactive DecayWhen the nucleus of a radioactive isotopedecays, emitting ionizing radiation, thenucleus is transformed into a different isotope, called a decay product. The new isotope may be stable or unstable. If it is unstable, it will continue to decay, changing itsnucleus and emitting more ionizing radiation. Several decays may occur before a stable isotope is produced. (Figure 3)1What istheNature ofRadiation?RadioactiveDecayFigure 3.Radioactive DecayForms of Ionizing RadiationIonizing radiation can take two differentforms: Electromagnetic waves which spread out inall directions through space at the speedof light. High-energy particles which travel throughspace at various rates.Examples of ionizing radiation include: X-rays (used in medicine and forscientific research) and Gamma rays (emitted by some materials,including the sun and stars and soil).Source: The Ohio State University Extension13

U N D E R S TA N D I N G R A D I AT I O N I N O U R WO R L DFigure 4.Types ofIonizingRadiationProtonAlpha Particle(positive charge)NeutronElectron1Beta Particle(negative charge)EnergyWhat istheNature ofRadiation?Source: The Ohio State University ExtensionHalf-lifeTypes andSources ofIonizingRadiationThe half-life is the time it takes for one-halfof a radioactive isotope’s atoms to decay.For example, suppose that several atoms ofa radioactive isotope with a half-life ofthree hours were isolated and observed.After three hours, one-half of thoseradioactive atoms would remain. The otherhalf would have decayed into different isotopes. After three more hours, only half ofthe remaining radioactive atoms (onefourth of the original number) wouldremain unchanged.The half-life can vary substantially fromone isotope to another, ranging from a fraction of a second for plutonium-214, to 8days for iodine-131, to 24,000 years forplutonium-239, to billions of years foruranium-238.The half-life of an isotope determines thelongevity of its radioactivity. The longerthe half-life, the more atoms it takes to givea certain amount of radioactivity. However,the half-life of a radioactive material is nota direct measure of the risk associated withthe material. (See Determining Levels ofRisk, Chapter 3, page 41.)14Gamma Ray(Figure 4) X-rays, another important type ofradiation, arise from processes outside of thenucleus.Alpha RadiationAn alpha particle is composed of two neutrons and two protons in a tight positivelycharged bundle that has escaped from thenucleus of a heavy radioactive element,such as uranium or radium, during radioactive decay.Alpha radiation is relatively slow-moving,has little penetrating power, and can bestopped by a single sheet of notebookpaper or the dead outer layer of skin tissue.(Figure 5) Therefore, alpha-emittingradioisotopes are not usually a hazardoutside the body.However, when alpha-emitting materialsare ingested or inhaled, energy from the alphaparticles is deposited in internal tissues suchas the lungs and can be harmful. (See TheHealth Effects of Radon, Chapter 3, page37.)Beta RadiationTypes and Sources ofIonizing RadiationBeta particles are fast-moving free electronsemitted during radioactive decay. They canbe either negatively or positively charged.A positively charged beta particle is called apositron.The major types of ionizing radiationemitted as a result of radioactive decay arealpha and beta particles and gamma rays.A beta particle is small—less than 1/7000of the weight of an alpha particle—and ittravels farther through solid material than

U N D E R S TA N D I N G R A D I AT I O N I N O U R WO R L DFigure 5. Penetrating Power of Different Types of RadiationGlass orAluminumConcreteor LeadPaper1AlphaWhat istheNature ofRadiation?BetaGammaalpha particles. Beta particles can travel significant distances in air. However, mostbeta particles can be reduced or stopped bya layer of clothing, eyeglasses, or a few millimeters of a substance such as aluminum.(See Figure 5)Although more penetrating than alpha particles, beta particles are less damaging overthe same distance. Some beta particles canpenetrate the skin and cause tissue damageespecially to the eyes. However, both alphaand beta emitters are generally more hazardous when they are inhaled or ingested.Humans can be exposed to beta particlesfrom both manmade and natural sources.Tritium, carbon-14, and strontium-90 areexamples of radionuclides that emit betaparticles upon decay.Gamma RadiationLike visible light and X-rays, gamma raysare photons—weightless packets of energy.Gamma rays often are emitted from aradioactive nucleus along with alpha or betaparticles. They have neither a charge normass and are very penetrating.Most gamma rays can pass completelythrough the human body. This may causeionization and possible health effects in anyorgan of the body. Most gamma rays losealmost all their energy in a few feet of soil,three feet of concrete, or six inches of lead.Types andSources ofIonizingRadiationA naturally-occurring source of gamma raysin the environment is potassium-40.Manmade sources include iodine-131 (produced in nuclear reactors, accelerators, andnuclear explosions) and cobalt-60 (also created in nuclear reactors) which is used infood irradiation. (See Food Irradiation,Chapter 3, page 29.)X-raysX-rays are emitted from processes occurringoutside the nucleus. They have essentiallythe same properties as gamma rays, but aregenerally lower in energy and therefore lesspenetrating than gamma rays. A few millimeters of lead can stop X-ray.X-ray machines are widely used in medicinefor diagnosis and treatment, and in industryfor examinations, inspections, and processcontrols. Because of this heavy use, X-raysare the largest source of manmade radiationexposure. Due to their very short wavelength, X-rays can pass through materials,such as wood, water, and flesh. They can bemost effectively stopped by heavy materialslike lead or by substantial thickness ofconcrete.15

U N D E R S TA N D I N G R A D I AT I O N I N O U R WO R L DNeutronsOne source of ionizing radiation resultsfrom the release of neutrons during nuclearfission. Neutrons are released during nuclearfission, which may occur spontaneously orduring a nuclear reaction, when a free neutron collides with a nucleus.1What istheNature ofRadiation?Types andSources ofIonizingRadiation16Neutrons have a neutral electrical charge,so they may be readily absorbed by thenuclei of other atoms, creating new radioactive isotopes. Fission fragments and neutron-activated material are responsible forthe intense radioactivity on the inside surfaces of nuclear reactors.(Material for this chapter is adapted fromWhat Is Radioactive Material and How Does ItDecay? (RER-20) and What Is IonizingRadiation? (RER-21), Ohio State UniversityExtension.)

U N D E R S TA N D I N G R A D I AT I O N I N O U R WO R L D2Where Does Radiation Come From?Sources of Ionizing Radiation Cosmic radiationWhen energy particles and rays are expelledfrom the forces that bind them together inatoms, ionizing radiation is emitted (seeIonizing Radiation, Chapter 1, page 12).This process has been going on since thebirth of the universe. Radiation has alwaysbeen commonplace in our world. Internal radiation from natural elementsin our bodies (such as radioactive potassium) and some foods that contain smallquantities of radioactive elements (suchas radium-226 in eggs, and potassium-40in bananas and some vegetables)Natural radioactive materials were discovered in the 1890s. It was not until 1942that physicist Enrico Fermi and his teamcreated the first manmade radioactive materials in the world’s first nuclear reactor atthe University of Chicago. (see Chronology,page 93)Measuring Radiation ExposureManmade RadiationIn the years since these discoveries, themanmade sources and uses of radiation havemultiplied so that manmade radiation isnow commonplace. We use radiation to: Generate electricity, Diagnose and treat medical problems,In the United States, we commonly measure human exposure to potentially harmfulradiation in units called millirem (one onethousandth of a rem). (See MeasuringHuman Exposure, Chapter 3, page 32.)The remaining 18 percent of our radiationexposure is from manmade sources (Figure6): X-rays and other medical and dental procedures Breed more productive and disease resistant crops, and Consumer products (such as cigarettes,smoke detectors, color televisions) Conduct a wide range of scientificresearch. Operation of nuclear power plantsHowever, most of the ionizing radiation weare exposed to consists of natural, or background, radiation:MeasuringRadiationExposureOn average, each of us receives about 360millirem of radiation each year. About 300millirem, or 82 percent of the total, is natural background radiation (from radon andother natural sources). Create and improve consumer products,Natural RadiationWhereDoesRadiationComeFrom? Manufacture of nuclear weapons Fallout from past atmospheric nuclearweapons testing Radon gas Other terrestrial sources (radioactive elements in rocks, soil, water, and plants)17

U N D E R S TA N D I N G R A D I AT I O N I N O U R WO R L DFigure 6. Sources of Radiation ExposureOtherConsumer 1%Nuclear ProductsMedicine SourcesRadon55%Source: National Council on RadiationProtection and MeasurementsNatural SourcesEverything on Earth is exposed to a constant barrage of naturally occurring ionizingradiation from the sun, cosmic rays, andradioactive elements in the Earth’s crust.The primary radioactive elements in theEarth’s crust are uranium, thorium, potassium, radium, and their radioactive decayproducts or derivatives.RadonRadon is a naturally occurring gas formedfrom the radioactive decay of uranium-238in rock and soil. Radon is colorless, odorless, tasteless, chemically inert, and radioactive. Radon also decays, emitting ionizingradiation in the form of alpha particles, andtransforms into decay products, or “progeny” radioisotopes. The half-life of radon isabout four days. Unlike radon, the progenyare not gases, and can easily attach to andbe transported by dust and other particles inair. The decay of progeny continues untilstable, non-radioactive progeny are formed.At each step in the decay process, radiationis released. Radon accounts for more thanhalf (an average of 55 percent) of the radiation dose we receive each year and is thesecond leading cau

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.