Study Guide Radon Measurement - NACHIeducation.nachi.org/coursemedia/course-58/documents/... ·...

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StudyGuideforRadonMeasurementServiceProviderCourseThisstudyguidecanhelpyou:

• takenotes;• readandstudyoffline;• organizeinformation;and• prepareforassignmentsandassessments.

AsamemberofInterNACHI,youmaycheckyoureducationfolder,transcript,andcoursecompletionsbyloggingintoyourMembers-OnlyAccountatwww.nachi.org/account.Topurchasetextbooks(printedandelectronic),visitInterNACHI’secommercepartnerInspectorOutletatwww.inspectoroutlet.com.Copyright©2007-2015InternationalAssociationofCertifiedHomeInspectors,Inc.

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StudentVerificationandInteractivityStudentVerificationByenrollinginthiscourse,thestudentherebyatteststhats/heisthepersoncompletingallcoursework.S/heunderstandsthathavinganotherpersoncompletethecourseworkforhimorherisfraudulentandwillresultinbeingdeniedcoursecompletionandcorrespondingcredithours.Thecourseproviderreservestherighttomakecontactasnecessarytoverifytheintegrityofanyinformationsubmittedorcommunicatedbythestudent.Thestudentagreesnottoduplicateordistributeanypartofthiscopyrightedworkorprovideotherpartieswiththeanswersorcopiesoftheassessmentsthatarepartofthiscourse.Ifplagiarismorcopyrightinfringementisproven,thestudentwillbenotifiedofsuchandbarredfromthecourseand/orhavehis/hercredithoursand/orcertificationrevoked.Communicationonthemessageboardorforumshallbeofthepersoncompletingallcoursework.

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IntroductionWelcometoInterNACHI'sfreeonlineRadonMeasurementServiceProvidercourse.Uponsuccessfulcompletionofthiscourse,thestudentshallbeableto:

• comprehendthefundamentalsaboutradongas;

• understandthescienceofradonandradioactivity;

• communicatehealthrisksofradonexposure;

• performradontestingaccordingtomeasurementprotocols;• performaninspectionofaradonmitigationsystem;• understandtherequirementsforNEHA-NationalRadonProficiencyProgram

certification;• understandtherequirementsforformerUSEPARadonProficiencyPrograms;• performaninspectionofradonpreventionbuildingtechniques;• taketheNEHANationalRadonProficiency(NEHA-NRPP)Measurementexam.

TheRadonMeasurementServiceProvidercourseincludes:

• 16ContinuingEducationCEs;• 20sections;• 216photosanddiagrams;• 7quizzes;• 100-questionfinalexam(drawnfromalargerpool);• instantgrading;• adownloadable,printableCertificateofCompletion;and• accreditationsandstateapprovals.

Thecoursecoversthefollowingcategories:

• Introduction• WhatisRadon?• RadiationandRadioactivity• WhatisanAtom?• DecayChains• Curies,EquationsandER• HealthRisks• RadoninWater• CurieandBecquerel

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• Alpha,BetaandGamma• TheGeologyofRadon• RadonEntryintoaHouse• RadonMeasurement:GeneralDiscussion• ProtocolsforRadonMeasurements• IndoorRadonandRDPMeasurementProtocols• EPAandASTMMitigationStandards• EPA'sRadonMitigationStandards• ModelStandards• BuildingRadonOut• InterNACHISOPforInspectingRadonSystems• RadoninWater,RemovalMethods

Acknowledgment

ThiscoursedrawsuponmanyresourcesprovidedbytheInternationalAssociationofCertifiedIndoorAirConsultants(www.iac2.org),theInternationalAssociationofCertifiedHomeInspectors(www.nachi.org),andtheUnitedStatesEnvironmentalProtectionAgency(EPA).

Informationfoundinthiscoursemayalsobefoundinthefollowingdocuments:

• InterNACHI's"InternationalStandardsofPracticeforInspectingRadonMitigationSystems"

• "IonizingRadiationFactBook,"U.S.EPA,Document402-F-06-061,March2007• "FederalProvincialTerritorialRadiationProtection"• "StandardPracticeforInstallingRadonMitigationSystemsinExistingLow-Rise

ResidentialBuildings,"ASTMInternational,DocumentE2121-03• InterNACHI'sInternationalStandardsofPracticeforInspectingCommercial

Properties• "RadonMitigationStandards,"U.S.EPA,Document402-R-93-078,October1993

(revisedApril1994)• "BuildingRadonOut,"U.S.EPA,Document402-K-01-002,April2001• "StandardPracticeforRadonControlOptionsfortheDesignandConstructionof

NewLow-RiseResidentialBuildings,"ASTMInternational,DocumentE1465-07a• "ModelStandardsandTechniquesforControlofRadoninNewResidential

Buildings,"U.S.EPA,Document402-R-94-009• "IndoorRadonandRadonDecayProductMeasurementsDeviceProtocols,"EPA

DocumentNumber402-R-92-004,July1992• "ProtocolsforRadonandRadonDecayProductMeasurementsinHomes,"U.S.EPA,

DocumentNumber402-R-93-003,June1993• "ACitizen'sGuidetoRadon,"EPADocumentNumber402-K-02-006,September

2005

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• "Consumer'sGuidetoRadonReduction:HowtoReduceRadonlevelsinYourHome,"U.S.EPA,Document402-K-03-002,RevisedFebruary2003

• "HomeBuyer'sandSeller'sGuidetoRadon,"U.S.EPA,402-K-05-005,May2005• "StandardPracticeforInstallingRadonMitigationSystemsinExistingLow-Rise

ResidentialBuildings,"U.S.EPA,Document402-K-03-007• "TechnicalSupportDocumentforthe1992CitizensGuidetoRadon,"U.S.EPA,

Document400-R-92-011,May1992• "RadonReductionTechniquesforExistingDetachedHouses,TechnicalGuidance

(3rdEdition)forActiveSoilDepressurizationSystems,"U.S.EPA,Document625-R-93-011,October1993

• "RadonProficiencyProgram(RPP)Handbook,"U.S.EPA,Document402-R-95-013,July1996

• "ResidentialStandardsofPractice,"InternationalAssociationofCertifiedHomeInspectors

• "RadonMitigationResearch,"U.S.EPA,Document600-F-94-035,September1994• variousdocumentsprovidedbystateenvironmentalandhealthdepartmentsand

HealthCanada

Disclaimer

Whiletheinformationinthisdocumentisbelievedtobeaccurate,theauthorsandcontributorsdonotmakeanywarranty,guaranteeorrepresentation,expressedorimplied,withrespecttotheaccuracy,effectivenessorusefulnessofanyinformation,methodormaterialinthisdocument,nordotheyassumeanyliabilityfortheuseofanyinformation,methodsormaterialsdisclosedherein,orfordamagesarisingfromsuchuse.Usersofthisinformationareencouragedtosecureprofessionaladviceforspecificmeasurementmethods,techniquesandstandards.Thestudentmustcontacttheappropriatestate/provinceregulatorybodyordepartmenttodetermineandcomplywiththerequirementsforperformingradonmeasurementservicesinthatstateorprovince.Takingthiscoursealonemaynotqualifyoneas"certified"byastate/provinceregulatingbodyordepartment.Furthermore,anyreferencestospecificproductsareprovidedsolelyasexamples,andarenotendorsementsoftheproduct.

Section1:WhatIsRadon?WhatIsRadon?

Radonisagasproducedbytheradioactivedecayoftheelementradium.Radioactivedecayisanatural,spontaneousprocessinwhichanatomofoneelementdecaysorbreaksdowntoformanotherelementbylosingatomicparticles(protons,neutronsorelectrons).Whensolidradiumdecaystoformradongas,itlosestwoprotonsandtwoneutrons.Thesetwo

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protonsandtwoneutronsarecalledanalphaparticle,whichisatypeofradiation.Theelementsthatproduceradiationarereferredtoasradioactive.Radonitselfisradioactivebecauseitalsodecays,losinganalphaparticleandformingtheelementpolonium.

Elementsthatarenaturallyradioactiveincludeuranium,thorium,carbonandpotassium,aswellasradonandradium.Uraniumisthefirstelementinalongchainofdecaythatproducesradiumandradon.Uraniumisreferredtoasthe"parent"element,andradiumandradonarecalled"daughters"or"progeny."Radiumandradonalsoformdaughterelementsastheydecay.Theprogenyofradonarecalledradondecayproducts,orRDPs.Thedecayofeachradioactiveelementoccursataveryspecificrate.Howfastanelementdecaysismeasuredintermsoftheelement's"half-life,"ortheamountoftimeforone-halfofagivenamountoftheelementtodecay.Uraniumhasahalf-lifeof4.4billionyears,soa4.4-billion-year-oldrockhasonlyhalfoftheuraniumwithwhichitstarted.Thehalf-lifeofradonisonly3.8days.Ifajarwerefilledwithradon,onlyhalfoftheradonwouldbeleftafter3.8days.Butthenewly-madedaughterproductsofradon(orRDPs)wouldalsobeinthejar,includingpolonium,bismuthandlead.Poloniumisalsoradioactive.Itisthiselementwhichisproducedbyradonintheairandinpeople'slungsthatcanhurtlungtissueandcauselungcancer.

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Radioactivityiscommonlymeasuredinpicocuries(pCi).

Becausethelevelofradioactivityisdirectlyrelatedtothenumberandtypeofradioactiveatomspresent,radonandallotherradioactiveatomsaremeasuredinpicocuries.Forinstance,ahousehaving4picocuriesofradonperliterofair(4pCi/L)hasabouteight

ornineatomsofradondecayingeveryminuteineveryliterofairinsidethehouse.A1,000-square-foothousewith4pCi/Lofradonhasnearly2millionradonatomsdecayinginside

iteveryminute.

Radonlevelsinoutdoorair,indoorair,soilairandgroundwatercanbeverydifferent.Outdoorairrangesfromlessthan0.1pCi/Ltoabout30pCi/L,butitprobablyaveragesabout0.2pCi/L.Radoninindoorairrangesfromlessthan1pCi/Ltoabout3,000pCi/L,butitprobablyaveragesbetween1and2pCi/L.Radoninsoilair(theairthatoccupiestheporesinsoil)rangesfrom20or30pCi/Ltomorethan100,000pCi/L;mostsoilsintheUnitedStatescontainbetween200and2,000pCiofradonperliterofsoilair.Theamountofradondissolvedingroundwaterrangesfromabout100tonearly3millionpCi/L.

NaturalRadiationExposureSincethebeginningoftime,alllivingcreatureshavebeenexposedtoradiation.Weliveinaradioactiveworld.TherearemanynaturalsourcesofradiationwhichhavebeenpresentsincetheEarthwasformed.Inthelastcentury,wehaveaddedsomewhattothisnaturalbackgroundradiationwithartificialsources.However,thenaturallyoccurringsourcescontributeaboutfourtofivetimesmoreradiationthanhuman-madesources.Thethreemajorsourcesofnaturallyoccurringradiationare:•cosmicradiation;•sourcesintheearth'scrust,alsoreferredtoasterrestrialradiation;and•sourcesinthehumanbody,alsoreferredtoasinternalsources.

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CosmicTheEarthandalllivingthingsonitareconstantlybombardedbyradiationfromspace,similartoasteadydrizzleofrain.ChargedparticlesfromtheSunandstarsinteractwithEarth’satmosphereandmagneticfieldtoproduceashowerofradiation,typicallybetaandgammaradiation.ThedosefromcosmicradiationvariesindifferentpartsoftheworldduetodifferencesinelevationandtotheeffectsoftheEarth’smagneticfield.CosmicradiationcomesfromtheSunandouterspace,andconsistsofpositivelychargedparticles,aswellasgammaradiation.Atsealevel,theaveragecosmicradiationdoseisabout26millirems(mrem)peryear.Athigherelevations,theamountofatmosphereshieldingcosmicraysdecreasesand,thus,thedoseincreases.TheaveragedoseintheUnitedStatesisapproximately28mremperyear.

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TerrestrialRadioactivematerialisalsofoundthroughoutnature.Itisinthesoil,waterandvegetation.Lowlevelsofuranium,thoriumandtheirdecayproductsarefoundeverywhere.Thisiscalledterrestrialradiation.Someofthesematerialsareingestedwithfoodandwater,whileothers,suchasradon,areinhaled.Thedosefromterrestrialsourcesalsovariesindifferentpartsoftheworld.Locationswithhigherconcentrationsofuraniumandthoriumintheirsoilhavehigherdoselevels.Themajorisotopesofconcernforterrestrialradiationareuraniumanditsdecayproducts,suchasthorium,radiumandradon.Therearenaturalsourcesofradiationintheground,rocks,buildingmaterialsandpotablewatersupplies.Radongasisacurrenthealthconcern.Thisgasresultsfromthedecayofnaturaluraniuminsoil.Radon,whichemitsalpharadiation,risesfromthesoilunderhousesandcanbuildupinhomes,particularlywell-insulatedhomes.IntheUnitedStates,theaverageeffectivewhole-bodydoseofradonisabout200mremperyear,whilethelungsreceiveapproximately2,000mremperyear.

InternalInadditiontocosmicandterrestrialsources,allhumansarebornwithnaturallyoccurringradionuclides,suchasPotassium-40,Carbon-14,Lead-210,andotherisotopes.Thevariationindosefromonepersontoanotherisnotasgreatasthevariationindosefromcosmicandterrestrialsources.Theaverageannual"dose"frominternalradioactivematerialisabout40mrem.

IonizingRadiationExposuretothePublicThischartshowsthatofthetotaldoseofabout360milliremsperyear,naturalsourcesofradiationaccountforabout82%ofallpublicexposure,whileman-madesourcesaccountfortheremaining18%.

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Section2:RadiationandRadioactivityRadiationandRadioactivity

WhatisRadiation?

Radiationisenergythattravelsintheformofwavesorhigh-speedparticles.Whenweheartheword"radiation,"wegenerallythinkofnuclearpowerplants,nuclearweapons,andradiationtreatmentsforcancer.Wewouldalsobecorrecttoaddmicrowaves,radar,electricalpowerlines,cellphonesandsunshinetothelist.Therearemanydifferenttypesofradiationthathavearangeofenergyformingtheelectromagneticspectrum.Thesetypesofradiationhaveenoughenergytobreakchemicalbondsinmolecules,orremovetightlyboundelectronsfromatoms,thuscreatingchargedmoleculesoratomsknownasions.Thiskindofradiationisreferredtoas"ionizingradiation."

Ionizingradiationisenergyintheformofwavesorparticlesthathasenoughforcetoremoveelectronsfromatoms.Inthiscourse,wewillrefertoitsimplyasradiation.Onesourceofradiationisthenucleiofunstableatoms.Astheseradioactiveatoms(alsoreferredtoasradionuclidesorradio-isotopes)seektobecomemorestable,theirnucleiejectoremitparticlesandhigh-energywaves.Thisprocessisknownasradioactivedecay.

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Someradionuclides,suchasradium,uraniumandthorium,haveexistedsincetheformationoftheEarth.Theradioactivegas,radon,isonetypeofradioactivematerialproducedasthesenaturallyoccurringradio-isotopesdecay.Humanactivities,suchasthesplittingofatomsinanuclearreactor,canalsocreateradionuclides.Regardlessofhowtheyarecreated,allradionuclidesreleaseradiation.Themajortypesofradiationemittedduringradioactivedecayarealphaparticles,betaparticlesandgammarays.Radiationcancomefromnaturalsourcesandfrommanufacturedradionuclides.AhospitalX-ray,forexample,isatypeofmanufacturedradiation.

WhatisRadioactivity?Radioactivityisthepropertyofsomeatomsthatcausesthemtogiveoffenergyspontaneouslyasparticlesorrays.Radioactiveatomsemitionizingradiationastheydecay.

Section3:WhatIsanAtom?WhatIsanAtom?

Tobeabletounderstandradiationandradioactivity,weneedtounderstandthelanguageofatomicstructure.Atomsaretheextremelysmallparticlesofwhichwe,andeverythingaroundus,aremade.

DemocritusbyAntoineCoypel

Democrituswasapre-SocraticGreekmaterialistphilosopherinthe5thcenturyBC.Knownas"TheLaughingPhilosopher,"Democritusbelievedthatallmatterismadeupofvarious

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imperishable,indivisibleelements,whichhecalledatomaor"indivisibleunits,"fromwhichwegettheEnglishword"atom."Democritustheorizedthattheshapeofanobject'satomsdeterminethatobject'sphysicalcharacteristics.

HoustonAstrodome

Anatomisthesmallestbuilding-blockofmatter.Atomsaremadeofneutrons,protonsand

electrons.IfoneatomwerethesizeoftheHoustonAstrodome,itsnucleuswouldberoughlythesizeofapea.

DmitriMendeleevbyIlyaRepin

DmitriIvanovichMendeleev(1834–1907)wasaRussianchemistandinventor.HeiscreditedasbeingthecreatorofthefirstversionofthePeriodicTableofElements.Usingthetable,hepredictedthepropertiesofelementsyettobediscovered.

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Thereare92naturallyoccurringelements.Scientistshavecreatedmanyothers,bringingthetotalnumberofknownelementstomorethan100.Atomsarethesmallestunitsofanelementthatbehavethesameway,chemically,astheelementitselfdoes.

WhenMendeleevbegangroupingelements,hetooknoteoftheLawofChemicalPeriodicity,whichstates,"Thepropertiesoftheelementsareperiodicfunctionsofatomicnumber."ScientistsusethePeriodicTabletofindoutimportantinformationaboutvariouselements.ThePeriodicTableordersallknownelementsaccordingtotheirsimilarities,categorizingelementsby"groups"and"periods."Eachelementisorderedbyitsatomicnumber.Theatomicnumberisdeterminedbythenumberofprotonsperatom.Inanatomwithaneutralcharge,thenumberofelectronsequalsthenumberofprotons.ThePeriodicTablerepresentsneutralatoms.Theatomicnumberforagivenelementislocatedabovetheelement'ssymbol.Beneaththeatomicnumberistheatomicmassnumber.AtomicmassismeasuredinAtomicMassUnits,where1amu=(1/12)massofcarbonmeasuredingrams.Theatomicmassnumberisequaltothenumberofprotons,plusitsneutrons.Thisnumberisfoundbeneaththeelement'ssymbol.Whentwochemicalsreactwitheachother,thereactiontakesplacebetweenindividualatoms--attheatomiclevel.Theprocessesthatcausematerialstoberadioactive--toemitparticlesandenergy--alsooccurattheatomiclevel.

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AtomicStructureIntheearly20thcentury,aNewZealandscientistworkinginEngland,ErnestRutherford,andaDanishscientist,NielsBohr,developedatheoryaboutthestructureofanatomthatdescribesanatomaslookingverymuchlikeoursolarsystem.

Atthecenterofeveryatomisanucleus,whichiscomparabletotheSuninoursolarsystem.Electronsmovearoundthenucleusin"orbits,"similartothewayplanetsmovearoundtheSun.Whilescientistsnowknowthatatomicstructureismorecomplex,theRutherford-Bohrmodelisstillausefulapproximationtobeginunderstandingatomicstructure.

Anucleuscontainsprotonsandneutrons;together,thesearecallednucleons. Aneutronhasnoelectricalchargeand,likeaproton,isabout1,800timesasheavy

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asanelectron.

Aprotonisapositivelychargedparticle.Allatomsofanelement(radioactiveandnon-radioactive)havethesamenumberofprotons.Protonsandneutronsinthenucleus,andtheforcesamongthem,affectanatom'sradioactiveproperties.

Theparticlesthatorbitthenucleusasacloudarecalledelectrons.Theyarenegativelycharged,andtheybalancethepositiveelectricalchargeoftheprotonsinthenucleus.Interactionswithelectronsintheouterorbitsaffectanatom'schemicalproperties.

WhatHoldsAtomsTogether?

Thenucleusofanatomisheldtogetherbythestrongnuclearforceofattractionbetweennucleons:proton-to-proton,neutron-neutron,andproton-neutron.Itisextremelypowerful,butextendsonlyaveryshortdistance,aboutthediameterofaprotonorneutron.Oppositeelectricalchargesoftheprotonsandelectronsdotheworkofholdingtheelectronsinorbitaroundthenucleus.Electronsclosertothenucleusareboundmoretightlythantheouterelectronsbecauseoftheirdistancefromtheprotonsinthenucleus.Theelectronsintheouterorbits,orshells,aremorelooselyboundandaffectanatom'schemicalproperties.

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Therearealsoelectromagneticforceswhichtendtoshovethepositivelychargedprotonsand,asaresult,theentirenucleusapart.Incontrasttothestrongnuclearforce,theelectricalfieldofaprotonfallsoffslowlyoverdistance,extendingfarbeyondthenucleus,bindingelectronstoit.Thebalancebetweenthestrongnuclearforcepullingthenucleustogetherandthepositivechargesoftheprotonspushingitapartislargelyresponsibleforthepropertiesofaparticularkindofatomornuclide,auniquecombinationofprotons,neutrons,andbalanceofenergies.Thedelicatebalanceofforcesamongnuclearparticleskeepsthenucleusstable.Anychangeinthenumber,arrangementorenergyofthenucleonscanupsetthisbalanceandcausethenucleustobecomeunstableorradioactive.Disruptionofelectronsclosetothenucleuscanalsocauseanatomtoemitradiation.Theamountofenergyrequiredtobreakupthenucleusintoitspartsiscalledthe"bindingenergy."Itisoftenreferredtoas"cosmicglue."

AtomicShorthandAtomicShorthandRepresentingAtomicPropertiesAsscientistsidentifiedthenuclearpropertiesofelementsandfounddifferentformsofelements,theyneededaneasywaytowriteandkeeptrackofthebasicnuclearproperties.Theydevelopedashorthandthatcombinesthedefiningpiecesofinformationaboutthevariousformsofanelement:

Xstandsforthechemicalsymbol,Zrepresentsthenumberofprotons,andAisitsatomicmass.

(Refertothegraphicsaboveandbelowforanexampleofthisshorthand.)•ThechemicalsymbolfortheelementcarbonisC.•ThenumberofprotonsinthenucleusZisthesameforanyformofanelement.•Arepresentsthemassofoneatomoftheelementcarbon.•ThenumberofneutronsinthenucleusisequaltoAminusZ.Twodifferentforms,orisotopes,ofcarbonarerepresentedbelow.

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•Themostcommonformofcarbon(stablecarbon)isrepresentedbelowattheleftandhas6protons(and6neutrons),soithasanatomicmassof12.•Carbonthathas6protons(and8neutrons),andanatomicmassof14,isradioactiveandisusedincarbon-dating,whichisaprocessthatwasdevelopedtodeterminetheageofarcheologicalartifacts.

TheseformsofcarbonarecommonlyreferredtoasCarbon-12andCarbon-14,respectively.

Asthisclose-upofaPeriodTableillustrates,theRadon-222atomhas86protonsand,therefore,136neutrons,becauseitsatomicmassis222.Itsatomicnumberis86.Theatomofradonisidentifiedbyitsatomicmass,soitiscalledRadon-222.

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TheRutherford-BohrModelIntheearly20thcentury,scientistswerestrugglingtounderstandthestructureofatoms.Theyhadpartsoftheanswer.Theelectron,whichhasanegativeelectricalcharge,hadbeendiscoveredearlier.Theyknewthatthebasicatomhadnooverallcharge.Together,thesepiecesofinformationmadeitnaturaltoassumethattheatomalsocontainedsomethingthatcarriedapositivecharge.Scientistsguessedthatsinceelectronsareextremelysmall,whateverthispositivematterormaterialwas,itmustmakeupmostofthemassofanatomandbemuchlargerthantheaspectsalreadyidentified.

ErnestRutherfordNielsBohrScientistsErnestRutherfordandNielsBohrdevelopedatheorythatdescribedthearrangementofthepropertiesofanatomassimilartooursolarsystem.KnownastheRutherford-BohrTheoryofAtomicStructure,itwasabreakthroughinunderstandingthewaytheatomworks.Rutherfordconductedexperimentsinwhichheshotrelativelylarge,chargedalphaparticlesatapieceofthingoldfoil.Hefoundthatmostoftheparticlespasseddirectlythroughthefoil,butsomebouncedoffatoddangles,asthoughtheyhadbeendeflected.Fromtheseresults,Rutherfordconcludedthateachatomwasmostlyemptyspace,butalsocontainedadenseregion--acentralmass--whichhisalphaparticlescouldnotpassthrough.Healsoconcludedthatthiscentralmassmusthaveapositivechargeinordertodeflectthepositivelychargedalphaparticles.RutherfordandBohrtheorizedthatanatom'spartsoperatesimilarlytooursolarsystem.Atthecenterofeveryatomisanucleus,whichiscomparabletotheSun.Electronsmove

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aroundthenucleusin"orbits,"similartothewayplanetsmovearoundtheSun.Eachorbitaroundthenucleusrepresentsanenergylevel,andelectronscannotexistinbetweenorbits.Orbitsclosertothenucleushavelowerenergy.Ifenergyisadded,anelectroncanbe"excited"tojumptoahigherenergylevel--anorbitfartherawayfromthenucleus.Eventually,theelectronwillreturntoitsoriginalstate,andtheatomwillgiveoffenergyequaltothedifferencebetweenthetwoorbits.Insomematerials,theenergyisgivenoffasX-rays.Othermaterialsproducespecificcolorsofvisiblelight,orothertypesofelectromagneticenergy.Eachorbitcanholdonlyacertainnumberofelectrons.Thelower-energyorbitsmustfillupfirst,iftheatomistobeatits"ground"state.Thisisthelowestenergystateand,therefore,itsmoststablestate.Withmoreresearch,scientistsdiscoveredthatatomicstructureismorecomplex,andthattheRutherford-Bohrmodelcontainedseriousflaws.TheRutherford-Bohrmodelprovidedthefirstreallyusefulviewoftheatom.Itmatchedwhatscientistsknewaboutchemicalreactionsandthewayatomsbehaved.Itledtosomepredictionsthatwerelaterprovencorrect.Bohrhadrectifiedaseriousflawbyrecognizingthatelectronshadtobeinorbitsorenergystates.Buthisanalysisoftheenergygivenoffwhenanelectrondroppedfromahigher-energyorbittoalower-energyorbitdidn'tholdupforatomsbiggerthanhydrogen,whichisthesimplestatom,withonlyoneprotonandnoneutrons.Moreworkneededtobedoneonthemodel.ImprovingtheRutherford-BohrModel:TheSchrödingerTheoryoftheAtom

ErwinSchrödinger

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GermanscientistErwinSchrödingerthoughttheproblemwiththeRutherford-Bohrtheorymightbeinconfiningtheelectronstospecificorbits.Otherscientistshaddevelopedtheideathatelectromagneticenergyactedlikeawavesometimes,andlikeaparticleatothertimes.Schrödingerthoughtthatelectronsmightworkthesameway.Iftheelectronsdidbehavelikeelectromagneticenergy,wecouldn'tknowexactlywhereanindividualelectronwas.Wecouldonlyknowtheprobabilityofitsbeinginaparticularplace.

Schrödinger's"ElectronClouds"

SchrödingerreplacedBohr'swell-definedorbitswithprobability"clouds,"alsoknownas"orbitals."Hecouldcalculatetheprobabilitythatanelectronwouldbeataparticularspotintheorbital,butnotknowforsure.Insomeregionsoftheorbital,therewasahighprobabilitythatanelectronwouldbethere.Inotherregions,therewasalowprobabilityofthepresenceofelectrons.Theprobabilitydistributionsoforbitalsaresometimesshownas"lobes"extendingawayfromthenucleusinthreedimensions.

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(a) (b) (a)TheRutherford-Bohrmodelshowsdistinctelectronorbits.(b)Schrödinger’smodelshows"electronclouds"ororbitals.Schrödinger’sidea,andtheequationsheusedtopredictwhereelectronswouldbe,solvedproblemsthatBohr'smodelhadn't.Italsogavescientistsabetterunderstandingoftheelectronandhowitbehavesinchemicalreactions.Schrödinger’stheoryofthenatureofelectronsalsoledtoresearchinsemiconductorsandothertechnologiesonanatomicscale.Despiteitstechnicalflaws,theRutherford-Bohrmodelisstillusefulbecauseitissimpleandhelpsusunderstandbasicatomicstructure.

WeighingAtoms:AtomicMassUnits

Atomsaresosmallthatitdoesn'tmakesensetousethesameunitsformeasuringthemthatweuseeveryday,likeouncesorgrams.Tomakeiteasiertoworkwithatomicweights,earlyradiationscientistsdevelopednewunitsofmeasurementonamoreappropriatescale.Theydecidedtousethemassofawell-knownandverycommonelementasthebasisformeasurementsofatomicmass.Thenewscaleequatedoneatomicmassunit(AMU)tothemassofthemostcommoncarbonatom,whichhas6protonsand6neutrons,dividedby12.So,oneAMUisaboutthesameasoneproton,andalsoaboutthesameasoneneutron(sinceelectronsaresomuchsmallerthattheycontributeverylittletothemassofanatom).

OneAMUislessthan1.66x10-24gram,whichis0.00000000000000000000000166ofagram.

TheInternationalSystemofUnits,orSIUnitsandDerivedSIUnits

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PrefixSymbolDecimalFactor

yottaY1000000000000000000000000=1024zettaZ1000000000000000000000=1021exaE1000000000000000000=1018petaP1000000000000000=1015teraT1000000000000=1012gigaG1000000000=109megaM1000000=106kilok1000=103hectoh100=102decada10=101-----------------1-------------------------------------------------decid0.1=10-1centic0.01=10-2millim0.001=10-3microµ0.000001=10-6nanon0.000000001=10-9picop0.000000000001=10-12femtof0.000000000000001=10-15attoa0.000000000000000001=10-18zeptoz0.000000000000000000001=10-21yoctoy0.000000000000000000000001=10-24

WhySomeAtomsAreRadioactiveWhyaresomeatomsradioactive?Thebalanceoftheforcesinthenucleusofanatomdetermineswhetheranucleusisstableorunstable(radioactive).Atomsfoundinnatureareeitherstableorunstable.Anatomisstableiftheforcesamongtheparticlesthatmakeupthenucleusarebalanced.Anatomisunstableorradioactiveiftheseforcesareunbalanced--ifthenucleushasanexcessofinternalenergy.Unstableatomsarecalledradionuclides.Theinstabilityofaradionuclide'snucleusmayresultfromanexcessofeitherneutronsorprotons.Anunstablenucleuswillcontinuallyvibrateandcontortand,soonerorlater,attempttoreachstabilitybysomecombinationofmeans,such

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as:•ejectingneutronsandprotons;•convertinganeutrontoaproton(orviceversa)withtheejectionofabetaparticleorpositron;or•releasingadditionalenergybyphotonorgamma-rayemission.Canunstableatomsbecomestable?Yes.Astheunstablenucleusemitsradiationasitdisintegrates,theradionuclidetransformstodifferentnuclides.Thisprocessiscalledradioactivedecay.Itwillcontinueuntiltheforcesinthenucleusarebalanced.Forexample,asaradionuclidedecays,itwillbecomeadifferentisotopeofthesameelementifthenumberofneutronschanges.Itmaybecomeadifferentelementaltogetherifthenumberofprotonschanges.Often,whenaradionuclidedecays,thedecayproduct--thenewnuclide--isalsoradioactive.Thisistrueformostnaturallyoccurringradioactivematerials,andforsomefissionproducts.Inordertobecomestable,thesematerialsmustgothroughmanysteps,becomingaseriesofdifferentnuclidesandgivingoffenergyasparticlesorraysateachstep.Theseriesoftransformationsthatagivenradionuclidewillundergo,aswellasthekindofradiationitemits,arecharacteristicoftheradionuclide.Thisiscalledadecaychain.

DecayChainbyTosaka

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Howlongdoradionuclidesstayradioactive?Itdependsonthekindofradioactivematerial.Therateofdecayisoneofthecharacteristicsofradionuclides.Scientiststalkaboutthisrateasaradionuclide'sradioactivehalf-life.Itisthetimerequiredforthedisintegrationofone-halfoftheradioactiveatomsthatarepresentwhenmeasurementstarts.Itdoesnotrepresentafixednumberofatomsthatdisintegrate,butafraction.Foranygivenradionuclide,itshalf-liferemainsconstant.What'sthedifferencebetweenradiationandradioactivity?Radiationistheenergythatisreleasedasparticlesorraysduringradioactivedecay.

Radioactivityisthepropertyofanatomthatdescribesspontaneouschangesinitsnucleusthatcreateadifferentnuclide.Thesechangesusuallyhappenasemissionsofalphaorbetaparticles,andoftengammarays.Everytimeanucleusemitsparticlesorenergy,thisisreferredtoasadisintegration.Thenumberofdisintegrationsperunit-time,ortherateofemission,iscalledtheactivityofasample.Sinceeachdisintegrationtransformstheatomintoanewnuclide,"transformation"isoftensubstitutedfor"disintegration"whentalkingaboutradioactivedecayandactivity.Activityisexpressedinbecquerelsorcuries,withcuriesbeingtheoriginalunitandwhichisusedmorecommonlyintheU.S.Onebecquerelequalsonetransformationpersecond.Onecurieequals37billiondisintegrationspersecond,butwasoriginallydefinedasthenumberofdisintegrationsofonegramofpureradiumpersecond.

Isallionizingradiationthesame?No.Anionisanatom(oragroupofatoms)thathasacquiredanetelectricchargebygainingorlosingoneormoreelectrons.Ionizingradiationishigh-energyradiationwhichiscapableoftransformingintoionsthesubstancesthroughwhichitpasses.Itcanbeintheformofalphaorbetaparticlesorgammarays(photons),andeachformbehavesdifferently.Thekindofradiationgivenoffbyanucleusdependsonthenatureoftheimbalanceinthenuclearforces.

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AlphaParticles

Alphaparticlesareenergetic,positivelychargedparticlesconsistingoftwoprotonsandtwoneutrons.Theyarecommonlyemittedintheradioactivedecayoftheheaviestradioactiveelements,suchasUranium-238,Radium-226andPolonium-210.Eventhoughtheyarehighlyenergetic,thehighmassofalphaparticlesmeanstheymoveslowlythroughtheair.Theeffectsonhumanhealthfromalphaparticlesdependprimarilyuponmethodofexposure.Externalexposure(forexample,bytouch)isoffarlessconcernthaninternalexposure,becausealphaparticleslacktheenergytopenetratetheouterlayerofskin,orevenasheetofpaper.

However,radionuclidesthatemitalphaparticlesinternallycanbeveryharmful.Ifalphaemittersareinhaled,ingested(swallowed)orabsorbedintothebloodstream(throughacutintheskin,forexample),sensitivelivingtissuecanbeexposedtoalpharadiation.

Alphadecayisatypeofradioactivedecayinwhichalphaparticlesarereleasedfromthenucleiofatoms.Theatomicnucleusemitsanalphaparticle(twoprotonsandtwoneutronsboundtogetherintoaparticle),andthentransforms(ordecays)intoanatomwithamass

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numberwhichis4less,andwithanatomicnumberwhichis2less.Example:Uranium-238(U-238)➔Thorium-234+Helium-4Becauseoftheirrelativelylargemass,+2chargeandrelativelylowvelocity,alphaparticlesareverylikelytointeractwithotheratomsandlosetheirenergy,sotheirforwardmotioniseffectivelystoppedwithinafewcentimetersofair.Beingrelativelyheavyandpositivelycharged,alphaparticlestendtohaveaveryshort"meanfreepath"(ortheaveragedistanceaparticletravelsbetweencollisionswithotherparticles),andtheyquicklylosekineticenergywithinashortdistancefromtheirsource.ThisresultsinseveralMeV(millionelectronvolts)beingdepositedinarelativelysmallvolumeofmaterial.Thisincreasesthechanceofcellulardamageincasesofinternalcontamination.

Ingeneral,externalalpharadiationisnotharmfulsincealphaparticlesareeffectivelyshieldedbyafewcentimetersofair,apieceofpaper,orthethinlayerofdeadskincells.Alphaparticlesarelowinpenetratingpower.Eventouchinganalphasourceisusuallynotharmful,thoughmanyalphasourcesalsoareaccompaniedbybeta-emittingradondaughters,andalphaemissionisalsoaccompaniedbygamma-photonemission.Ifsubstancesemittingalphaparticlesareingested,inhaled,injectedorintroducedthroughtheskin,thenitcouldresultinameasurabledoseofharmfulradiation.

BetaParticles

Betaparticlesarehigh-energy,high-speedelectronsorpositronsemittedbycertaintypesofradioactivenuclei,suchasPotassium-40.Thebetaparticlesaretheelectronsarisingfromtheconversionofaneutrontoaprotonandelectron,andarereleasedbytwoothershort-livedRDPs(radondecayproducts).Betaparticlesareemittedfromthenucleusduringradioactivedecay.Thebetaparticlesemittedareaformofionizingradiationalsoknownasbetarays.Theproductionofbetaparticlesistermedbetadecay.Anunstableatomicnucleuswithanexcessofneutronsmayundergobetadecay.

Betaparticleshaveahighercapacitytopenetratethanalphaparticlesdo,buttheyarelessdamagingoverequaldistances.Theycantravelfarintheairbutcanbesloweddownor

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stoppedbyalayerofclothing,orbyafewmillimetersofasubstancesuchasaluminum.Humansareexposedtobetaparticlesfrombothfabricatedandnaturalradiationsources,suchastritium,Carbon-14andStrontium-90.

Betaparticlescannotbestoppedbyasheetofpaper.Somebetaparticlescanbestoppedbyhumanskin,butsomeneedathickershield(likewood)tostopthem.Somebetaparticlesarecapableofpenetratingtheskinandcausingradiationdamageintheformofskinburns.However,aswithalpha-emitters,beta-emittersaremosthazardouswhentheyareinhaledoringested.Forexample,ifingested,someradionuclidesthatemitbetaparticlesmightbeabsorbedintothebones.

GammaRaysandX-RaysGammaRays

LikevisiblelightandX-rays,gammaraysareweightlesspacketsorbundlesofenergycalledphotons.Gammaraysoftenaccompanytheemissionofalphaorbetaparticlesfromanucleus.Theyhaveneitherachargenoramassandhavethestrongestpenetratingforce.Gammarayswillpenetratepaper,skin,wood,andothersubstances.Severalfeetofconcreteorafewinchesofleadmayberequiredtostopgammarays.OnesourceofgammaraysintheenvironmentisnaturallyoccurringPotassium-40.FabricatedsourcesincludeCobalt-60andCesium-137.Gammaraysarearadiationhazardforhumans.Whilegammarayscaneasilypasscompletelythroughthebody,afractionofthemwillalwaysbeabsorbedbyhumantissueandremainthere.Gammaradiationcancauseseveredamagetointernalorgans.However,theamountofgammaraysemittedbyradonanditsRDPsisnotnearlyasdamagingtothelungsasalphaparticles.

X-RaysX-raysarehigh-energyphotonsproducedbytheinteractionofchargedparticleswithmatter.X-raysandgammarayshaveessentiallythesameproperties,buttheydifferinorigin.X-raysareproducedeitherfromachangeintheelectronstructureofanatom,ortheyareproducedbymachines.X-raysareemittedfromprocessesoccurringoutsidethenucleus,whilegammaraysoriginateinsidethenucleus.X-raysalsoaregenerallylowerinenergyand,therefore,lesspenetratingthangammarays.AfewmillimetersofleadcanstopX-rays.LiterallythousandsofX-raymachinesareuseddailyinmedicineandindustryforexaminations,inspectionsandprocesscontrols.Becauseoftheirmanyuses,X-raysarethesinglelargestsourceoffabricatedradiationexposure.

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SummaryoftheCharacteristicsofRadioactiveMatter:

• alphaparticle:massivesize;chargeof+2e;slowspeed;

• betaparticle:verysmallsize;chargeof-1e;highspeed;and

• gammaray:nomass;nocharge;travelsatthespeedoflight.

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QuizonSections1,2&3Radonisagasproducedbytheradioactivedecayoftheelement________.

• radium• uranium• lead• polonium

Whensolidradiumdecaystoformradongas,itlosestwo_______andtwoneutrons.

• protons• neutrons• electrons• atoms

Radonitselfisradioactivebecauseitalsodecays,losinga/n______particleandformingtheelementpolonium.

• alpha• little• electrostatic• power

_________isthefirstelementinalongseriesofdecaythatproducesradiumandradon.

• Uranium• Radon• Lead• Bismuth

Uraniumhasahalf-lifeof____billionyears.

• 4.4• 1.2• 0.5• 44

Thehalf-lifeofradonisonly___days.

• 3.8• 2• 5.83• 4

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_____________isenergyintheformofwavesorparticlesthathasenoughforcetoremoveelectronsfromatoms.

• Ionizingradiation• Radion-nuclear• Visiblelight• Radon

T/F:Alphaparticleslacktheenergytopenetratetheouterlayerofdeadskin.

• True• False

T/F:Similartobetaparticles,alphaparticlescauseabout20timesmoredamageinsidethelungs.

• True• False

Section4:DecayChainsDecayChainsMostnaturallyoccurringradioactivematerialsandmanyfissionproductsundergoradioactivedecaythroughaseriesoftransformations,ratherthaninasinglestep.Untilthelaststep,theseradionuclidesemitenergyorparticleswitheachtransformationandbecomeanotherradionuclide.Thisseriesofdecay,knownasadecaychain,endsinastablenuclide.Forexample,Uranium-238decaysthroughaseriesofstepstobecomeastableformoflead.Eachstepintheillustrationbelowindicatesadifferentnuclide.(Notethatonlyafewofthestepsarelabeled,andthenumbersbeloweachlabelindicatethelengthoftheparticularradionuclide'shalf-life.)At4.5billionyears,Uranium-238hasthelongesthalf-lifeofanyknownelement.Radon-222hastheshortesthalf-lifeat3.8days.ThelastradionuclideinthedecaychainpicturedisPolonium-210,whichtransformsintoLead-210,andeventuallyintothestablenuclideLead-206.

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Theradioactivedecaychainforradonbeginswithuranium.Uraniumdecaystoproduceradium,whichthendecaysintoradon.RadonthendecaysintootherRDPs(orradondecayproducts),whicharealsoradioactive.RDPsaredifferentfromactualradonisafewways.ThecharacteristicsofRDPsinclude:•Theyarethesourceofcelldamageinthelungs.•Theyareshort-livedproducts(lessthan30minutes),butthemostsignificant.•Theyhavestaticelectricalcharges.•Theyarechemicallyreactive.•Theyaresolidparticles,ratherthangases,thatactlikeinvisibleaerosolsintheair.•Theyareclassifiedasheavymetals.Allofthesecharacteristicsmakethedecayproductscapableofeasilyattachingthemselvestosolidobjectssuchasdust,smoke,walls,floors,clothing,oranyotherobjects.IftheRDPsattachtosurfaces,theyarenolongerfloatingintheairandaresaidto“plateout."Iftheyattachtoductsorsmokeparticles,theycanbecarriedintothelungswheretheycancauselungcancer.

Ingrowth

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Theincreasingconcentrationofdecayproductsandactivityiscalledingrowth.Theillustrationbelowshowsingrowthwhenthedecayproductisstableandtheoriginalradionuclideisreplaced.Inthissituation,theactivitydecreaseswithdecayoftheoriginalradionuclide.

Howcanwepredicthowmuchradioactivitywillbeproduced?

Thepatternofingrowthvariesaccordingtotherelativelengthofthehalf-livesoftheoriginalradionuclideanditsdecayproducts.Undercertainconditions,decayproductsundergotransformationatthesameratetheyareproduced.Whenthisoccurs,radioactiveequilibriumexists.Whetherequilibriumoccursalsodependsontherelativelengthsofthehalf-lifeofradionuclidesandtheirdecayproducts.Usingequationsthataccountforhalf-lives,therateofingrowth,whetherequilibriumoccurs,theoriginalamountofradionuclide,andthestepsinthedecaychain,scientistscanestimatetheamountofactivitythatwillbepresentatvariouspoints.

RadonIngrowthDuringUraniumDecayTheimportanceofunderstandingdecaychainsisillustratedbytheingrowthofRadon-222duringthedecayofUranium-238.Uraniumwasdistributedwidelyintheearth'scrustasitformed.GiventheageoftheEarth,uranium'sslowlyprogressingdecaychainnowcommonlyproducesRadon-222.Itisradioactiveandhasseveralcharacteristicsthatmagnifyitshealtheffects:•Radonisagas.Itpenetratessoilandcracksinrocksintotheair.Itcanseepthroughfoundationsintohomes(particularlybasements),andaccumulateintofairlyhighconcentrations.

•Radondecayemitsalphaparticles,theradiationthatpresentsthegreatesthazardtolungtissue.

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•Radon'sveryshorthalf-life(3.8days)meansthatitemitsalphaparticlesatafastrate.

RadonandUraniumMinersAhigher-than-expectedleveloflungdiseaseinuraniumminerscalledattentiontotheeffectsofRadon-222.Theminersworkedlonghoursinenclosedspaces,surroundedbyuraniumoreandradonthatseepedoutoftherock.Healthworkersexpectedtoseehealthproblemsintheminersthatwouldreflectdirectexposuretoradiation.Instead,thepredominanthealthproblemswerelungcancerandotherlungdiseases.First,thehealthworkerssuspectedthedustitself.Theyknewthathighconcentrationsofsmallparticles,suchascoaldust,asbestosandcottonfibers,coulddamageworkers'lungs.However,closerexaminationofUranium-238'sdecaychainidentifiedRadon-222asthemostlikelyculpritoftheworkers'lungdiseases.

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Half-LifeTherateofradioactivedecayischaracteristicofeachradionuclide.Scientiststalkaboutthisrateasaradionuclide'sradioactivehalf-life.Itisthetimerequiredforthedisintegrationofone-halfoftheradioactiveatomsthatarepresentwhenmeasurementstarts.Itdoesnotrepresentafixednumberofatomsthatdisintegrate,butonlyafraction.Forexample,ifthereare100atomsofaradionuclidethathasahalf-lifeofoneminute,therewillbeone-halfthatnumber,or50atomsoftheoriginalradionuclideleftoneminutelater.Afterthesecondminute,therewillbe25atomsoftheoriginalradionuclideleft.Thefactthatthissimpleexamplepointstotheexistenceof12.5radioactiveatomsafterthreeminutesillustratesthatahalf-lifeisintendedtobeusedfortheverylargenumberofatomsthatarefoundinevensmallsamplesofradioactivematerials.One-hundredatomsaren'tgoingtogiveoffmuchradiation.Thehalf-lifereferstohowquicklytheradioactivityfromaradionuclidewilldecrease.Itsnumberofcuriestellshowactiveitisnow.Eachradioactiveelementintheradondecaychainhasadifferenthalf-life.Half-lifeisthetimerequiredforhalfoftheatomsoftheelementtodecay.Itisnotthetimeforalloftheatomstodecay.Ifyouhaveanamountofradonwithahalf-lifeof3.8days,bytheendof3.8days,youwillhavehalfasmuch.Another3.8dayslater,youwillhavehalfthatamount,andsoon.Usually,bythetime10half-liveshavepassed,thereisverylittleleft.Itisimportanttounderstandthehalf-lifeprocessbecauseitisthistimeperiodthatradonanditsdecayproductshavetobedispersedintotheenvironment.Aperiodof3.8daysislongenoughforradontomovethroughseveralfeetofsoil.Thefirstfewradondecayproductshaveshorthalf-lives,butiftheyareinhaled,theycancauseradiationdamagetotheinnerliningofthelungsbeforetheycanbeexhaled.Radongas,likeCarbon-14gas,isnaturallyoccurringinourenvironment.ItformsduringthedecayofUranium-238,anelementwithafairlyinterestingdecaysequence.

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Thegraphicaboveisillustratestheradiumoruraniumseries.

Radonhasnostableisotopes.However,36radioactiveisotopeshavebeencharacterized,withtheiratomicmassesrangingfrom193to228.Themoststableisotopeis222Rn,whichisadecayproductof226Ra,adecayproductof238U.Averytraceamountofthe(highlyunstable)isotope218Rnisalsoamongthedaughtersof222Rn.

Therearethreeotherradonisotopesthathaveahalf-lifeofoveranhour:211Rn,210Rnand224Rn.The220Rnisotopeisanaturaldecayproductofthemoststablethoriumisotope(232Th),andiscommonlyreferredtoasthoron.Ithasahalf-lifeof55.6secondsandalsoemitsalpharadiation.Similarly,219Rnisderivedfromthemoststableisotopeofactinium(227Ac)—named"actinon"—andisanalphaemitterwithahalf-lifeof3.96seconds.Noradonisotopesoccursignificantlyintheneptunium(237Np)decayseries,thoughatraceamountofthe(extremelyunstable)isotope217Rnisproduced.

222Rnbelongstotheradiumanduranium-238decaychain,andhasahalf-lifeof3.8235days.Itsfourfirstproducts(excludingmarginaldecayschemes)areveryshort-lived,meaningthatthecorrespondingdisintegrationsareindicativeoftheinitialradondistribution.Itsdecaygoesthroughthefollowingsequence:

•222Rn,3.8days,alphadecayingto...•218Po,3.10minutes,alphadecayingto...•214Pb,26.8minutes,betadecayingto...

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•214Bi,19.9minutes,betadecayingto...•214Po,0.1643ms,alphadecayingto...•210Pb,whichhasamuchlongerhalf-lifeof22.3years,betadecayingto...•210Bi,5.013days,betadecayingto...•210Po,138.376days,alphadecayingto...•206Pb,stable.

Theradonequilibriumfactoristheratiobetweentheactivityofallshort-periodradonprogenies(whichareresponsibleformostofradon'sbiologicaleffects),andtheactivitythatwouldbeatequilibriumwiththeradonparent.

Ifaclosedvolumeisconstantlysuppliedwithradon,theconcentrationofshort-livedisotopeswillincreaseuntilanequilibriumisreachedwheretherateofdecayofeachdecayproductwillequalthatoftheradonitself.Theequilibriumfactoris1whenbothactivitiesareequal,meaningthatthedecayproductshavestayedclosetotheradonparentlongenoughfortheequilibriumtobereached,withinacoupleofhours.UndertheseconditionseachadditionalpCi/Lofradonwillincreaseexposure,by0.01WL(seeexplanationofWLbelow).Theseconditionsarenotalwaysmet;inmanyhomes,theequilibriumfractionistypically40%;thatis,therewillbe0.004WLofprogenyforeachpCi/Lofradoninair.[28]210Pbtakesmuchlonger(decades)tocomeinequilibriumwithradon,but,iftheenvironmentpermitsaccumulationofdustoverextendedperiodsoftime,210Pbanditsdecayproductsmaycontributetooverallradiationlevelsaswell.

Becauseoftheirelectrostaticcharge,radonprogeniesadheretosurfacesordustparticles,whereasgaseousradondoesnot.Attachmentremovesthemfromtheair,usuallycausingtheequilibriumfactorintheatmospheretobelessthanone.Theequilibriumfactorisalsoloweredbyaircirculationorairfiltrationdevices,andisincreasedbyairbornedustparticles,includingcigarettesmoke.Inhighconcentrations,airborneradonisotopescontributesignificantlytohumanhealthrisk.Theequilibriumfactorfoundinepidemiologicalstudiesis0.4.

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SummaryofCharacteristicsRadon-222:•isagas;•isodorless;•istasteless;•isinvisible;•mixeswithair;•ischemicallyinert(ornon-reactive);•isfoundeverywhere;•decaysbyalpha-particleemission;and•hasahalf-lifeof3.8days.

RadonDecayProducts,orRDPs:•aresolids,calleddaughtersorprogeny;•arechemicallyactive;•areelectricallycharged;•canattachtoairparticlesandclingtosurfaces;•havearatioofprogeny-to-radongasrangingfrom0.3to0.7ER(equilibriumratio),averaging0.5ER;•areshort-lived(from0.2millisecondsto26.8minutes);•includePolonium-218,214and210,whicharealpha-particleemitters,andthesealpha-particleemissionscancausephysicalcellulardamage,suchaslungcancer.

Section5:Curies,EquationsandERSection5:Curies,EquationsandER

Sincesmallamountsofmaterialcontainverylargenumbersofatoms,smallsamplescanhaveaverylargenumberofatomsdisintegratingatthesametime.Itdidn'ttakeradiationscientistsverylongtodecidethatworkingwithactivitiesinthebillions-of-disintegrations-per-secondwastooawkward.Tomakemeasuringtheactivitymoreconvenient,theydevelopedanewunit,thecurie,namedinhonorofMarieCurie,apioneerinthestudyofradioactivematerials.Radioactivematerialsaremeasuredincuries.Apicocurieisone-millionthofamillionth(oratrillionth)ofacurie.Howbigisacurie?Acurieisdefinedas37billiondisintegrationspersecond.Thecuriewasoriginallya

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comparisonoftheactivityofasampletotheactivityofonegramofradium.Whenmoreaccuratetechniquesmeasuredaslightlydifferentactivityforradium,thereferencetoradiumwasdropped.Aradioactivesamplethathasanactivityof74billiondisintegrationspersecondhasameasuredactivityof2curies.

Aretheresmallerandlargerunitsofactivity?Thecurie,abbreviatedas"Ci,"isaverylargeunitforsomepurposes,andaverysmallunitforothers.Scientistsusethefollowingfractionsormultiplesofacurie,aswell:•picocuries(pCi)are1million-millionthofacurie(1x10-12Ci).Picocuriesareusedinmeasuringthetypicallysmallamountsofradioactivitythatarepresentinairandwater.

•megacuries(MCi)are1millioncuries(1x106Ci),andareusedinmeasuringtheverylargeamountsofradioactivityreleasedfromnuclearweapons,forexample.

•otherfractions,suchas:•amillicurie(1/1,000Ci=mCi),and•ananocurie(1billionthofacurie=nCi)areusedasneeded.TermsandMoreEquations:

• curie(Ci):astandardmeasurementforradioactivity,specificallytherateofdecayforagramofradium=37billiondecayspersecond.Aunitofradioactivityequalto3.7x1010disintegrationspersecond.

• picocurie(pCi):measurestherateoftheradioactivedecayofradon.OnepCiisonetrillionthofacurie,0.037disintegrationspersecond,or2.22disintegrationsperminute.

• picocurieperliter(pCi/L):aunitofradioactivitycorrespondingtoanaverageofonedecayevery27secondsinavolumeofoneliter,or0.037decayspersecondaliterofairorwater:1pCi/L=37becquerelspercubicmeter(Bq/m3).

• becquerel(Bq):TheSIorInternationalSystemofUnits'definitionofactivityis1Bq=1disintegrationpersecond.Onepicocurieperliterofradonisthesameas37bequerelspercubicmeter.

Theamountofradonintheairismeasuredin"picocuriesperliterofair,"or"pCi/L,”whichisthenumberofradioactivedisintegrationsperminuteinaliterofair.ApCi/Lis2.22

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disintegrationsperminuteforeachliter.Ifagalloncontainerheldairwith4pCi/L,therewouldbeabout4(quartspergallon)multipliedby4(pCi/L)multipliedby2.22disintegrationsperminutes,orabout35.2disintegrationsperminutesofradonatomsinthecontainer.Testresultsaresometimesexpressedinworkinglevels(WL),ratherthaninpicocuriesperliter(pCi/L),usingthisformula:4pCi/L=0.016WL.Radondecayproductsaremeasuredinworkinglevels(WL).Anycombinationofshort-livedradondecayproductsinoneliterofairwillresultintheultimateemissionof1.3x105MeV(millionelectronvolts)ofpotentialalphaenergy.Thisnumberwaschosenbecauseitrepresentstheapproximateamountofalphaenergyreleasedfromthedecayproductsinequilibriumwith100pCiofRn-222.Oneworkinglevelistheconcentrationofshort-livedRDPsproducedfromoneliterofaircontaining100pCiofradon.Theaverageindoorradonlevelis1.3pCi/L.

Theaverageoutdoorradonlevelis0.4pCi/L.

TheEPA'sactionlevelforradonis4pCi/L.TheEPA'sactionlevelforradonis0.02WL.

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EquilibriumRatioThereisarelationshipbetweendecay-productconcentrationandradon-gasconcentration.Radonissaidtobeat"secularequilibrium"withitsdecayproductswhentheradioactiveactivityofradonanditsdecayproductsarethesame.Theequilibriumratioforradonisexpressedthisway:equilibriumratio=(WLx100)÷(pCi/L).Atcompleteequilibrium(i.e.,atanequilibriumratioof1),1WLofRDPsispresentwhentheradonconcentrationis100pCi/L.Butduetoventilationandplate-out,theRDPsneverreachequilibriuminaresidentialenvironment,sotheratioisnever1insideahouse.Thecommonlyassumedequilibriumratiois0.5--thedecayproductsarehalfwaytowardequilibrium--inwhichcase,1WLwouldcorrespondto200pCi/L.However,equilibriumratiosvarywithtimeandlocation,andratiosof0.3to0.7arecommon.

RDPsAtomsofradioactiveradongasdecaybytheemissionofalphaparticles,andtransformintoPolonium-218and,inturn,transformtoPolonium-214bysuccessivealphaemission.

DaughtersIntheairoftheaverageroom,bothradonandthetworadioactiveisotopesofPoloniumarepresent(214and218),andareoftenreferredtoasradonprogenyorradondecayproducts(RDPs).Thesemaystayfreeormayattachtoroomaerosol(suchasdustorsmoke).Itistheseradonprogenythatgetdepositedinairwaysandcausetheprimaryriskofinhalation.Radongasitselfdoesnotposemuchrisk.

ActionLevelBasedontheactualriskobservedinuraniumminers,theU.S.EnvironmentalProtectionAgencyhassettheaction-levellimitat0.02WL.Becauseradondaughterproductscangetdepositedinventilationsystemsandonothersurfaces,theydonotreachequilibriumwithradon.Basedonsomeexperimentaldatafromtypicalhomes,theEPAassumesthattheequilibriumratiois50%.Theaction-levellimitof0.02WLcorrespondstothederivedradonconcentrationof4pCi/Lwhentheequilibriumratiois50%.

Therearetwomethodsofcharacterizingradon:eithermeasureradon-gasconcentration,ormeasureradon-progenyconcentration.TheEPA'saction-levellimitis4pCi/Lforradongas,and0.02WLforradonprogeny.Thesemeasurementsareequivalenttoeachotheronlywhenequilibriumratiois50%.Bothmeasurementsareacceptable,aslongasEPA-listed

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devicesandmethodsareused.(ThesearealsonowlistedasNEHAorNRSB.)Onceradonentersahome,itbeginstoformdecayproducts.Someactivitiesinsidethehomemayaffecttheequilibrium.Air-filteringwouldremovesomeofthedecayproducts,butnottheradon,becauseitisaninertgas.AirleakagemightallowsomeoftheRDPstoescape.RDPsmightclingtoor“plateout”onwalls,floorsandotherobjects.AllofthesefactorscanpreventtheRDPsfromreachingthemaximumconcentration.Theywilleventuallyreachafinalconcentration,whichisabalanceoftheamountofRDPsthatareproducedandarelostthroughplate-outandventilation.Itisthisbalancethatisreferredtoastheequilibriumratio.Inahome,ittypicallytakesabout12hoursforthisequilibriumtobeachieved,afterthedoorsandwindowshavebeenclosed.

AssumptionInordertorelatethemeasurementofradontoanequivalentamountofradondecayproducts,itisnecessarytoassumearatiooftheamountofradondecayproductsthatareproducedandavailableforinhalationfromtheamountofradonintheair.That’swhattheequilibriumratio(ER)is.ERcanbecalculatedas:EquilibriumRatio=WorkingLevelx100÷RadonConcentration,orER=(WLx100)÷Rn.Forexample,iftheradonconcentrationis75pCi/L,andthedecay-productconcentrationis0.3WL,theequilibriumratiowouldbecalculatedasfollows:ER=(0.3)x(100)÷75=0.4Thisassumption--theequilibriumratio--cameaboutfromextensiveresearchandstatisticsavailablewhenradoninhomesandbuildingswasstartingtobeinvestigated.Theassumptionof50%,whichisusedtoday,isbasedonresidentialstructureswithaverageair-recirculationrates,withatypicalrangeofsuspendedradondecayproductsbetween30%to70%.

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Thisassumedequilibriumrateof50%equatesto.02WLmeasurements,whichistheEPA'sestablished"actionlevel."Radon=WLx100÷0.54(radon)=.02(radondecayproducts)x100÷0.5(assumedequilibriumratio)ER≠1Again,anequilibriumratioof1willnotlikelyoccurinanyhousebecauseventilationremovesbothradonandRDPs.RDPshaveanelectrostaticchargeandwillplateoutbyclingingtowalls,floors,furnitureandothersolidobjects.ThisreducestheRDPconcentrationwithoutaffectingtheradonconcentration.AndittakesawhileforradonenteringthehousetoproduceRDPs.Asaresult,theERwillalwaysbelessthan1.TheequationER=(WLx100)÷Rncanbearrangedtocalculatethedesiredexpression:ER=(WLx100)÷RnorWL=(RnXER)÷100orRn=(WLx100)÷ER

Iftheradonlevelismeasuredat4pCi/Landtheworkinglevelsaremeasuredat0.02WL,thentheequilibriumratio(ER)isequalto0.02x100÷4=0.5,or50%.

Unattachedparticles(whicharesolid,electricallychargedparticles)canbeinhaledandbecomelodgedinthelungs.Whentheysticktoobjectssuchasdust,smokeandpollen,RDPscanstillpresentahealthhazardiftheobjectissmallenoughtofloatinthe

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air.Rememberthatiftheyplateoutonawall,theyarenotahazard.Ifairisbeingcirculatedbyfans,alotoftheRDPscanplateoutonthewalls,floors,furnitureandothersolidobjects.Workinglevelscanbeloweredbyusingfans.Theradonconcentrationwillstaythesame,buttheERwillbelower.TheERisalsolowerafterahousehasbeenventilatedwithoutdoorair.ThesoilgasenteringahousehasverylowdecayproductsbecauseRDPswillplateoutinthesoil.Therefore,ifahouseisventilatedandthenclosedup,ittakesseveralhoursforthedecayproductstoreturntoanexpectedequilibriumofradonconcentration.FactorsAffectingtheEquilibriumRatioIncreasedairmovementcausesmoreofthehazardousRDPstoadheretofixedobjects,andtheydonotdetachonceintheymakecontactwithanobject.Thisdecreasestheamountofradondecayproductsavailableforinhalation,andalsodecreasestheequilibriumratio.Forinstance,inbuildingswithlargeairflowsorHEPAfilters,thepercentageofairborneradondecayproductscanbeconsiderablylowerthaninabuildingwithoutthem.Iftheindoorairisrelativelystable,withlittleairmovementthatwouldremoveRDPs,thentheERwilllikelybehigh,sincetherewillbemoredecayproductsintheair.Ifthereisahigh-efficiency,whole-houseair-filtersystemthatisoperatingwithahighdegreeofairmovement,thenalowERwouldbeexpected.

QuizonSections4&5Radondecayproducts(RDPs)aredifferentfromradoninafewways.Forexample,radondecayproductsareclassifiedasheavy________.

• metals• gases• fuels• particles

IftheRDPsattachtosurfaces,theyaresaidto?_______.?Theyarenolongerfloatingintheair.

• plateout• flake-out• electro-stat• saucer-in

T/F:Radon-222isagasthatisvisibleundercertainconditions.

• False

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• True

T/F:RDPsareelectricallycharged.

• True• False

RDPsareshort-lived,alllastinglessthan______minutes.

• 30• 2• 65• 0.5

T/F:TheradondecayproductsPolonium-218,214and210arealpha-particleemitters.

• True• False

T/F:Radondecayproductsaremeasuredinworkinglevels(WL).

• True• False

Radonissaidtobeat"secular___________"withitsdecayproductswhentheradioactivityofradon(oritsproductionrate)andtherateofdecayofitsRDPsarethesame.

• equilibrium• half-life• discord• concentrate

T/F:WL=(RnxER)?100

• True• False

Section6:HealthRisksRadonCausesLungCancerinNon-Smokers

ExposuretoRadonCausesLungCancerinNon-SmokersandSmokersAlikeLungcancerkillsthousandsofAmericanseveryyear.Smoking,radon,andsecond-handsmokearetheleadingcausesoflungcancer.Althoughlungcancercanbetreated,the

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survivalrateisoneofthelowestforthosewithcancer.Fromthetimeofdiagnosis,between11and15%ofthoseafflictedwilllivebeyondfiveyears.Inmanycases,lungcancercanbeprevented--thisisespeciallytrueforradon.Smokingistheleadingcauseoflungcancer.Smokingcausesanestimated160,000cancerdeathsintheU.S.everyyear,accordingto2008statisticsfromtheAmericanCancerSociety.Andtherateamongwomenisrising.In1964,Dr.LutherL.Terry,thenU.S.SurgeonGeneral,issuedthefirstwarningregardingthelinkbetweensmokingandlungcancer.LungcancernowsurpassesbreastcancerastheNumberOnecauseofcancerdeathsamongwomen.Asmokerwhoisalsoexposedtoradonhasamuchhigherriskoflungcancer.RadonistheNumberOnecauseoflungcanceramongnon-smokers,accordingtoEPAestimates.Overall,radonisthesecondleadingcauseoflungcancer.Radonisresponsibleforabout21,000lungcancerdeathseveryyear.About2,900ofthesedeathsoccuramongpeoplewhohaveneversmoked.Second-handsmokeisthethirdleadingcauseoflungcancerandisresponsibleforanestimated3,000lungcancerdeathseveryyear.Smokingaffectsnon-smokersbyexposingthemtosecond-handsmoke.Exposuretosecond-handsmokecanhaveseriousconsequencesforchildren’shealth,includingasthmaattacks.Itcanalsoaffecttherespiratorytractandmakethemvulnerabletobronchitisandpneumonia,etc.Itmayleadalsotoearinfections.ThefollowingWebsitesprovideawiderangeofcomprehensiveinformationaboutlungcancer,preventionandtreatment:

• AmericanCancerSociety:www.cancer.org• AmericanLungAssociation:http://www.lungusa.org/• NationalCancerInstitute:http://www.nci.nih.gov/• Vanderbilt-IngramCancerCenter:http://www.mc.vanderbilt.edu/vicc• MemorialSloan-KetteringCancer

Center:http://www.mskcc.org/mskcc/html/44.cfm

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RadonisaCarcinogenTwostudiesbasedonresearchconductedinNorthAmericaandinEuropeshowdefinitiveevidenceofanassociationbetweenresidentialradonexposureandlungcancer.Bothstudiescombineddatafromseveralresidentialstudies.Theywentastepbeyondearlierfindingsandconfirmedtheradonhealthriskspredictedbyoccupationalstudiesofundergroundminerswhobreathedradonforyears.Earlyinthedebateaboutradon-relatedrisks,someresearchersquestionedwhetheroccupationalstudiescouldbeusedtocalculaterisksfromexposuretoradoninthehomeenvironment.

“ThesefindingseffectivelyendanydoubtsabouttheriskstoAmericansofhavingradonintheirhomes,”saidTomKelly,directoroftheEPA’sIndoorEnvironmentsDivision.“Weknowthatradonisacarcinogen.Thisresearchconfirmsthatbreathinglowlevelsofradoncanleadtolungcancer.”

Whyisradonthepublichealthriskthatitis?TheEPAestimatesthatradonisresponsibleforabout20,000lungcancerdeathseachyearintheUnitedStates.Exposuretoradonisthesecondleadingcauseoflungcanceraftersmoking.Radonisanodorless,tastelessandinvisiblegasproducedbythedecayofnaturallyoccurringuraniuminsoilandgroundwater.Radonisaformofionizingradiationandaprovencarcinogen.Lungcanceristheonlyknowneffectonhumanhealthfromexposuretoairborneradon.Thusfar,thereisnoconclusiveevidencethatchildrenareatgreaterriskoflungcancerthanadults.Radoninairisubiquitous.Itisfoundinoutdoorairandintheindoorairofbuildingsofallkinds.TheEPArecommendsthattheproblembeaddressedifahome'sradonlevelis4pCi/L(picocuriesperliter)ormore.Becausethereisnoknownsafelevelofexposuretoradon,theEPAalsorecommendsthattheproblembeaddressedforhomeswithradonlevelsbetween2pCi/Land4pCi/L.TheaverageradonconcentrationintheindoorairoftheaverageAmericanhomeisabout1.3pCi/L.TheEPAbasesitsestimateof20,000radon-relatedlungcancersayearonthisnumber.Theaverageconcentrationofradoninoutdoorairis0.4pCi/L,orone-tenthoftheEPA’srecommended4pCi/Lactionlevel.

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Forsmokers,theriskoflungcancerissignificantduetothesynergisticeffectsofradonandsmoking.Forthisat-riskpopulation,about62peopleina1,000willdieoflungcancer,comparedtoaboutsevenpeopleina1,000whohaveneversmoked.Putanotherway,apersonwhohasneversmokedandisexposedto1.3pCi/Lhasa2-in-1,000chanceofdyingfromlungcancer,whileasmokerhasa20-in-1,000chance.Therisktosmokerscomparedtothosewhohaveneversmokedissixtimesgreater.Theradonhealthriskisunderscoredbythefactthat,in1988,theUnitedStatesCongressaddedTitleIIIonIndoorRadonAbatementtotheToxicSubstancesControlAct.ItcodifiedandfundedtheEPA’sthen-fledglingradonprogram.Thatsameyear,theSurgeonGeneralissuedawarningaboutradon,urgingAmericanstotesttheirhomesandtoreducetheradonlevel,whennecessary.Unfortunately,manyAmericanspresumethatbecausetheactionlevelis4pCi/L,aradonleveloflessthanthatisconsideredsafe.Thisperceptionisalltoocommonintheresidentialrealestatemarket.Inmanaginganyrisk,weshouldbeconcernedwiththegreatestrisk.FormostAmericans,theirgreatestexposuretoradonisinsidetheirhomes,especiallyinroomsthatarebelowgrade(suchasbasements),aswellasroomsthatareincontactwiththeground,andtheroomsdirectlyabovethem.

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LungCancerHowdoesradoninducecancer?Ifinhaled,radondecayproducts(Polonium-218andPolonium-214,solidform),unattachedorattachedtothesurfaceofaerosols,dustsandsmokeparticlesbecomedeeplylodgedinthelungswheretheycanradiateandpenetratethecellsofmucousmembranes,bronchi,andotherpulmonarytissues.Theionizingradiationenergyaffectingthebronchialepithelialcellsisbelievedtoinitiatetheprocessofcarcinogenesis.Althoughradon-relatedlungcancersaremainlyseenintheupperairways,radonincreasestheincidenceofallhistologicaltypesoflungcancer,includingsmall-cellcarcinoma,Adencarcinoma,andsquamouscellcarcinoma.Lungcancerduetoinhalationofradondecayproductsconstitutestheonlyknownriskassociatedwithradon.Instudiesdoneonminers,variablessuchasage,durationofexposure,timesinceinitiationofexposure,andespeciallytheuseoftobaccohavebeenfoundtoinfluenceindividualrisk.Infact,theuseoftobaccomultipliestheriskofradon-inducedlungcancerenormously.

Whatistheevidence?Moreisknownaboutthehealthriskofradonexposuretohumansthanaboutmostotherhumancarcinogens.Thisknowledgeisbasedonextensiveepidemiologicalstudiesofthousandsofundergroundminers,carriedoutovermorethan50yearsworldwide,includingonminersintheUnitedStatesandCanada.Inadditiontothedataonminers,experimentalexposuresonlaboratoryanimalsconfirmthatradonanditsdecayproductscancauselungcancer.

HumanStudiesandAnimalStudiesResearchonlungcancermortalityinminersexposedtoradonprogenyissubstantialandconsistent.Studiesofthousandsofminers,somewithfollow-upperiodsof30yearsandmore,havebeenconductedinmetal,fluorspar,shale,anduraniumminesintheUnitedStates,Canada,Australia,ChinaandEurope.Thesestudieshaveconsistentlyshownanincreaseintheoccurrenceoflungcancerwithexposuretoradondecayproducts,despitedifferencesinstudypopulationsandmethodologies.Theminerstudiesdetailedthefollowingfindings:•Atequalcumulativeexposures,lowexposuresintherangeoftheEPA's4pCi/Lactionleveloverlongerperiodsproducedagreaterriskoflungcancerthanhighexposuresovershortperiods.•Increasedlungcancerriskwithradonexposurehasbeenobservedevenaftercontrolling

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for,orintheabsenceof,otherexposurerisks,suchasasbestos,silica,dieselfumes,arsenic,chromium,nickel,andoredust.•Non-smokingminersexposedtoradonhavebeenobservedtohaveanincreasedriskoflungcancer.AnimalexperimentsconductedbytheUnitedStatesDepartmentofEnergy'sOfficeofEnergyResearch,aswellasthoseconductedinFrance,haveconfirmedthecarcinogenicityofradon,andhaveprovidedinsightintothenatureoftheexposure-responserelationship,aswellasthemodifyingeffectsoftheexposurerates.

Todate,theseanimalstudieshaveproducedseveralrelevantfindingsforhumans:•Healtheffectsobservedinanimalsexposedtoradonandradondecayproductsincludelungcarcinomas,pulmonaryfibrosis,emphysema,andashorteningoflifespan.•Theincidenceofrespiratorytracttumorsgrewwithanincreaseincumulativeexposurecoupledwithadecreaseinrateofexposure.•Increasedincidenceofrespiratorytracttumorswasobservedinratsatcumulativeexposuresaslowas20WLM.•Exposuretooredustordieselfumessimultaneouslywithradondidnotincreasetheincidenceoflungtumorsabovethatproducedbyradonprogenyexposuresalone.•Lifetimelung-tumorriskcoefficientsthathavebeenobservedinanimalsaresimilartothelifetimelung-cancerriskcoefficientsobservedinhumanstudies.•Inastudyofratsexposedtoradonprogenyanduraniumoredustsimultaneously,itwasobservedthattheriskoflungcancerwaselevatedatexposurelevelssimilartothosefoundinhomes.Theriskdecreasedinproportiontothedecreaseinexposuretoradonprogeny.In1988,apanelofexpertsconvenedbytheWorldHealthOrganization'sInternationalAgencyforResearchonCancerunanimouslyagreedthatthereissufficientevidencetoconcludethatradoncausescancerinhumansandinlaboratoryanimals.ScientificcommitteesassembledbytheNationalAcademyofSciences(NAS),theInternationalCommissiononRadiologicalProtection(ICRP),andtheNationalCouncilonRadiationProtectionandMeasurement(NCRP)alsohavereviewedtheavailabledataandagreedthatradonexposurecauseshumanlungcancer.

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Recognizingthatradonisasignificantpublichealthrisk,scientificandprofessionalorganizations,suchastheAmericanMedicalAssociation,theAmericanLungAssociation,andtheNationalMedicalAssociation,havedevelopedprogramstoreducethehealthrisksofradon.TheNationalInstituteforOccupationalSafetyandHealth(NIOSH)reviewedtheepidemiologicaldataandrecommendedthattheannualradonprogenyexposurelimitfortheminingindustrybelowered.Isoccupationalexposuretoradoncomparabletoresidentialexposure?Becausequestionshavebeenraisedabouttheappropriatenessofusingtheepidemiologicalstudiesofundergroundminersasabasisforestimatingtheriskradonposestothegeneralpopulation,theEPAcommissionedtheNAStoinvestigatethedifferencebetweenundergroundminersandmembersofthegeneralpublicinthedosestheyreceiveperunit-exposureduetoinhaledradonprogeny.TheNASreport,publishedin1991,concludedthatitisreasonabletoextrapolatefromtheminerdatatoaresidentialsituation,butthattheeffectivedosesperunitofexposureforpeopleintheirhomesareapproximately30%lessthanfortheminers.Initsanalysis,theNASconsideredvariablessuchastheamountandtypesofdusttowhichtheradondecayparticleswouldattach,thebreathingratesofworkingminerscomparedtothatofpeopleathome,andthepresenceofwomenandchildreninthehomes.TheEPAhasadjusteditsresidentialriskestimatesaccordingly.Theresultisstillconsiderable--itnowestimatesthatapproximately14,000lungcancerdeathsintheUnitedStatesannuallyareduetoresidentialradonexposures.Asmoredataaregatheredaboutresidentialradonexposures,theriskestimatesmaybeadjustedfurther.Enoughstatisticalevidenceexistsnow,however,tostatewithcertaintythat,eachyearintheUnitedStates,thousandsofdeathsduetopreventablelungcancerareattributabletoindoorresidentialexposuretoradon.Moreinformationisneededtoanswerimportantquestionsaboutradon'seffectonwomenandchildren--twogroupsnotincludedintheoccupationalstudies.Althoughchildrenhavebeenreportedtobeatgreaterriskthanadultsfordevelopingcertaintypesofcancerfromradiation,thereisnocurrentorconclusiveevidencethatradonexposureputschildrenatagreaterrisk.Somestudiesonminersandonanimalsindicatethat,forthesametotalexposure,alowerexposureoveralongerperiodismorehazardousthanbrief,highexposures.Thesefindingsincreaseconcernsaboutresidentialradonexposures.EpidemiologicalcontrolstudiesareunderwayintheU.S.andinEurope,thepooledresultsofwhichshouldenhancetheunderstandingoftheriskofresidentialexposuretoradon.

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Whataboutsmokingandradonexposure?Somepeopleaskwhetherthelungcancerdeathsattributedtoradonexposureactuallymaybetheresultofsmoking.A1989studybyresearchersfromNIOSH,theCentersforDiseaseControl,theHarvardSchoolofPublicHealth,andtheUniversityofCaliforniaatDavisdemonstratedagreatlyincreasedriskoflungcancerinnon-smokinguraniumminersexposedtohighradonconcentrations.Comparedtotypicalnon-smokingpopulations,theseminershadnineto12timestheriskofdevelopinglungcancer.EvidencefromsomeoftheepidemiologicalstudiesofAmericanundergrounduraniumminersindicatesthatradonexposureandsmokingmayhaveasynergisticrelationship.Eithersmokingorradonexposurecanindependentlyincreasetheriskoflungcancer;however,exposuretobothgreatlyenhancesthatrisk.Yourchancesofgettinglungcancerfromradondependmostlyon:•howmuchradonisinyourhome;•theamountoftimeyouspendinyourhome;and•whetheryouareasmoker,orhaveeversmoked.

RADONRISKforSMOKERS

RadonLevel

If1,000peoplewhosmokewereexposedtothislevelovera

lifetime...

Theriskofcancerfrom

radonexposurecomparesto...

WHATTODO:

Stopsmokingand...

20pCi/L

about260ofthemwouldgetlungcancer.

250timestheriskofdrowning.

mitigatetheexposurelevel.

10pCi/L


200timestheriskofdyinginahomefire.


8pCi/L


30timestheriskofdyinginafall.


4pCi/L


5timestheriskofdyinginacarcrash.


2pCi/L

about32ofthem

wouldgetlungcancer.

6timestheriskofdyingfrompoison.

considermitigationiflevelisbetween2and4pCi/L.

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1.3pCi/L

about20ofthem

wouldgetlungcancer.

(averageoutdoor

radonlevel)

understandthatreducingRnlevelsbelow2pCi/Lisdifficult.

0.4pCi/L

------------------

(averageoutdoor

radonlevel)

understandthatreducingRnlevelsbelow2pCi/Lisdifficult.

RADONRISKforPEOPLEWHOHAVENEVERSMOKED

RadonLevel

If1,000peoplewhohaveneversmokedwereexposedtothisleveloveralifetime...

Theriskofcancerfromradonexposurecomparesto...

WHATTODO:

20pCi/L about36ofthemwouldgetlungcancer.

35timestheriskofdrowning.

Mitigatetheexposurelevel.








thesameriskasdyinginacarcrash.


2pCi/L

about4ofthem

wouldgetlungcancer.

thesameriskasdyingfrompoison.

Considermitigationiflevelisbetween2and4pCi/L.

1.3pCi/L

about2ofthem

wouldgetlungcancer.

(averageindoorradonlevel)

UnderstandthatreducingRnlevelsbelow2pCi/Lisdifficult.

0.4pCi/L

-----------------

(averageindoorradonlevel)

UnderstandthatreducingRnlevelsbelow2pCi/Lisdifficult.

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GeneticDamageCausedbyRadon

Mostoftheepithelialcellulardamageisnotcausedbybreathinginradongasitself,whichisremovedfromthelungsduringexhalation,butbyradon'sshort-liveddecayproducts(half-lifemeasuredinminutesorless).Wheninhaled,thesedecayproductsmaybedepositedintheairwaysofthelungs.TheRDPssubsequentlyemitalphaparticlesastheydecayfurther.Thetotalamountofenergyemittedbytheprogenyisseveralhundredtimesthatproducedintheinitialdecayofradon.Theincreasedriskoflungcancerfromradonresultsprimarilyfromthesealphaparticlesirradiatinglungtissue.Whenanalphaparticlepassesthroughacell'snucleus,theperson'sDNAislikelytobedamaged.Morespecifically,availabledataindicatethatalphaparticlepenetrationofthecell'snucleusmaycausegenomicchanges,mosttypicallyintheformofpointmutationsandtransformations.

Sincealphaparticlesaremoremassiveandmorehighlychargedthanothertypesofionizingradiation,theyaremoredamagingtolivingtissue.Aspreviouslydescribed,alpharadiationisabletotravelonlyextremelyshortdistancesinthebody.Thus,alpharadiationfromdecayofradonprogenyinthelungscannotreachcellsinanyotherorgans,soitislikelythatlungcanceristheonlymajorcancerhazardposedbyradon.

Bybreakingtheelectronbondsthatholdmoleculestogether,radiationcandamagehumanDNA,theinheritedcompoundthatcontrolsthestructureandfunctionofcells.RadiationmaydamageDNAdirectlybydisplacingelectronsfromtheDNAmolecule,orindirectlybychangingthestructureofothermoleculesinthecell,whichmaytheninteractwiththeDNA.Thelattermechanismwillbedescribedinmoredetaillater.Whenoneoftheseevents

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occurs,acellcanbedestroyedquickly,oritsgrowthorfunctionmaybealteredthroughachange(mutation)thatmaynotbeevidentforseveralyears.Analphaparticleemittedfromradondaughterdecayisintheformofahigh-energyheliumion,knowninscientificnotationasHe2+.Theseheliumparticlestransverseacell'snucleiinalinearpatternanddepositenergyvialinearenergytransfer,orLET.Thisreferstotheenergytransferredperunitofpathtraveledbytheionizingparticle.Sincealphaparticlestravelshortdistancesandareslow,comparedtobetaandgammaparticles,theirefficiencyintransferringenergyandaffectinggenomicchangeisveryhigh,asistheirLETquantity.Oncedeposited,thisenergycausesDNAalterations,cell-cyclestress,andoccasionalcelldeath.Epithelialcellularchangescausedbythealphaparticleemissionfromasingleradondaughtercanbeseenwithamicroscope.

RiskAssessmentFacts

•TheEPA’sindoorradonprogrampromotesvoluntarypublicactionstoreducetherisksfromindoorradon.TheEPAandtheU.S.SurgeonGeneralrecommendthatpeopleperformasimplehometestusingkitswhicharenowwidelyavailableinstores.Ifhighlevelsofradonareconfirmed,itisrecommendedthatthosehighlevelsbemitigatedorreducedusingstraightforwardtechniques.•TheEPArecentlycompletedanupdatedassessmentoftheirestimatesoflungcancerrisksfromindoorradon,basedontheNAS's1999reportonradontitled"TheBiologicalEffectsofIonizingRadiation(BEIR)VI."Thisreportisthemostcomprehensivereviewofscientificdatagatheredonradon,andbuildsonandupdatestheirpreviousfindings.TheNASconcludedthathomeownersshouldstilltestand,ifnecessary,mitigatetheirexposuretoelevatedradonlevelsintheirhomes.•Radonisanaturallyoccurringradioactivegasthatiscolorless,odorlessandtasteless.It'snaturallyproducedfromtheradioactivedecayofuraniumthat'spresentinsoil,rockandgroundwater.Itemitsionizingradiationduringitsradioactivedecay,changingintoseveralradioactiveisotopesknownasradondecayproductsorRDPs.•Radongetsintotheindoorairprimarilyfromsoilunderbuildingstructures.Radonisaknownhumanlungcarcinogenandisthelargestsourceofradiationexposureandrisktothegeneralpublic.Mostinhaledradonisrapidlyexhaled,buttheinhaleddecayproductsreadilydepositinthelungtissuewheretheyirradiatesensitivecellsintheairways,increasingtheriskoflungcancer.•TheNASBEIRVIReportconfirmedtheEPA’slong-heldpositionthatradonisthesecondleadingcauseoflungcancer,andaseriouspublichealthproblem.TheNASestimatesthatradoncausesabout20,000lungcancerdeathseachyear.Thereportfoundthatevenverysmallexposurestoradoncanresultinlungcancer.Theyconcludedthatnoevidenceexiststhatshowsathresholdofexposurebelowwhichradonlevelsareharmless.Thereportalsofoundthatmanysmokersexposedtoradonfaceasubstantiallygreaterriskofgettinglungcancercomparedtothosewhohaveneversmoked.Thisisbecauseofthesynergisticrelationshipbetweenradonandcigarettesmoking.

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Section7:RadoninWaterPrivateWells

Propertyownerswithwellswhohaveconfirmedelevatedindoorradonlevelsshouldalsotesttheirwellwaterforradon.Radoninthewatersupplycanincreasetheindoorradonlevel,although,inmostcases,radonenteringthehomethroughwaterwillbeasmallsourceofriskcomparedtothelevelsofradonenteringthroughthesoil.TheEPAestimatesthatindoorradonlevelswillincreasebyabout1pCi/Lforevery10,000pCi/Lofradoninwater.(TheEPA'sOfficeofGroundWaterandDrinkingWaterhasdevelopedpublicationsrelatingtoradonindrinkingwaterwhichcanbefoundathttp://www.epa.gov/safewater/radon.html.)

Howisradontestedinwater?

Beforetestingforradonintheresidentialwatersupply,testtheair.Iftheindoorradonlevelishighandthehomeusesgroundwater,testthewater.Iftheradonlevelintheairislow,thereisnoneedtotestthewater.Testresultsareexpressedinpicocuriesofradonperliterofwater(pCi/L).Ingeneral,10,000pCi/Lofradoninwatercontributesroughly1pCi/Lofairborneradonthroughoutthehouse.TheEPAcurrentlyadvisesconsumerstotakeactionifthetotalhouseholdairlevelisabove4pCi/L.Forwaterborneradon,asimplestepistomakesurethatthebathroom,laundryroomandkitchenarewellventilated.Ifthewellwaterhasonlymoderatelevelsofradon,thismayadequatelyreduceexposuretowaterborneradon.However,ifthewellhashighlevelsofradon,considerusingwater-treatmentdevices,suchasgranularactivated-carbon(GAC)unitsandhomeaerators.

Whatdotheresultsofawatertestmean?

Itispossibletoestimatehowmuchtheradoninthewatersupplyisaffectingtheindoorradonlevel.Theformulatogaugewhetherindoorairlevelsareelevatedistosubtract1pCi/Lfromtheindoorairradonlevelforevery10,000pCi/Lofradonthatwasfoundinthewater.Forexample:Ifthereare30,000pCi/Lofradoninthewater,then3pCi/Loftheindoormeasurementmayhavecomefromradoninthewater.

Ifmostoftheradonisnotcomingfromthewater,mitigatetheindoorlevelsandthenre-testtheindoorairtomakesurethatthesourceofelevatedradonwasnotcomingfromtheproperty'swell.Ifalargecontributionoftheradoninthehouseiscomingfromthewatersupply,homeownerswanttoconsiderinstallingaspecialwatertreatmentsystemtoremoveradon.TheEPArecommendsinstallingawatertreatmentsystemonlywhenthereisaradonproblemfoundinthewatersupply.

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Howisradonremovedfromwater?

Radoncanberemovedfromwaterbyusingoneoftwomethods:aerationtreatment,orgranularactivated-carbon(GAC)treatment.

Aerationtreatmentinvolvessprayingwaterormixingitwithair,andthenventingtheairfromthewaterbeforeuse.

GACtreatmentfilterswaterthroughcarbon.Radonattachestothecarbonandleavesthewaterfreeofradon.Thecarbonmayneedspecialhandlingforitsdisposalifitisusedatahighradonlevel,orifithasbeenusedforalongtime.

Ineithertreatment,itisimportanttotreatthewaterwhereitentersthehome(atthepoint-of-entry)sothatallthewaterwillbetreated.Point-of-usedevices,suchasthoseinstalledonataporunderthesink,willtreatonlyasmallportionofthewaterandarenoteffectiveinreducingradoninthewater.Itisimportanttomaintainhomewatertreatmentunitsproperly.Failuretodosocanleadtootherwatercontaminationproblems.Somehomeownersoptforaservicecontractfromtheinstallertoprovideforcarbonreplacementandgeneralsystemmaintenance.

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Whereandhowdoesradongetintodrinkingwater?

Whilemostradon-relateddeathsareduetoradongasaccumulatedinhousesfromseepagethroughcracksinthefoundation,upto1,800deathsperyearareattributedtoradonfromthehousehold'swatersupply.Showering,washingdishesandlaunderingcandisturbthewaterandreleaseradongasintotheair.

Whataretherisksofradonexposure?

Radon'sprimarypublichealthriskisbybreathingintheindoorairofhomes.Thiscontributestoabout20,000lungcancerdeathseachyearintheUnitedStates,accordingtothe1999landmarkBEIRVIReportbytheNASonradoninindoorair.RadonisthesecondleadingcauseoflungcancerintheUnitedStates.BasedonasecondNASreportonradonindrinkingwater,theEPAestimatesthatradonindrinkingwatercausesabout168cancerdeathsperyear,89%fromlungcancercausedbybreathingradonreleasedfromwater,and11%fromstomachcancercausedbydrinkingradon-contaminatedwater.

Drinkingwaterthathashighlevelsofradonmaybeahealthrisk,butbreathingairhighinradonconcentrationismoreharmful.Breathinginradongasoveralongperiodoftimecanincreasetheriskoflungcancer.Drinkingwatercontaminatedbyradonmayincreasethechancesofdevelopingstomachcancer.

WhatshouldIdoifIhaveconcernsaboutradonexposure?

The1996SafeDrinkingWaterActAmendmentsrequiredtheEPAtoestablishseveralnew,health-baseddrinkingwaterregulations,includingamultimediaapproachtoaddressthepublichealthrisksfromradon.

Consultahealthcareprovidertodiscussconcerns,andconsiderusingoneofthetworadon-removalmethodspreviouslydiscussed(aerationtreatmentandGACtreatment).

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Section8:CurieandBecquerelPioneersintheDiscoveryofRadioactivity

MarieCurie

MarieCurie(1867-1934)andherhusband,PierreCurie(1859-1906),areperhapstwoofthemostfamousscientistsknownfortheircontributionstothestudyofradioactivity.PierrewasborninParisandMarieinPoland.TheybothstudiedattheSorbonne.Theyinvestigatedthepropertiesofuraniumandthoriumand,soonafter,discoveredpolonium.Pierrepursuedthestudyofmagnetismactingathightemperatures.Mariecontinuedherresearchinchemistryandphysics,andistheonlypersonevertoreceiveNobelPrizesinbothdisciplines.The"curie,"namedforher,istheunitofmeasurementnowusedinradiationresearch.TheCuriescombinedtheireffortswithHenriBecquerel,anotherscientist.In1903,theywereallawardedtheNobelPrizeinphysics.

AntoineHenriBecquerel

AntoineHenriBecquerel(1852–1908)wasaFrenchphysicistandNobellaureatewhowasresponsible,alongwithMarieandPierreCurie,forthediscoveryofradioactivity.Later,BecquereldemonstratedthattheradiationemittedbyuraniumsharedcertaincharacteristicswithX-rays,but,unlikeX-rays,thatradiationcouldbedeflectedbyamagneticfieldand,therefore,mustconsistofchargedparticles.The"becquerel"isalsoaunitofmeasurementinradiationstudies.

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Section9:Alpha,BetaandGammaAlpha,BetaandGammaParticles

ALPHAPARTICLES

Alphaparticles(symbolα)areatypeofionizingradiationejectedbythenucleiofsomeunstableatoms.Theyarelargesub-atomicfragmentsconsistingoftwoprotonsandtwoneutrons.

Whodiscoveredalphaparticles?

ErnestRutherford

Asdiscussedearlierinthiscourse,BritishscientistErnestRutherforddiscoveredalphaparticlesin1899whileworkingwithuranium.HisresearchcontributedtoourunderstandingoftheatomanditsnucleusthroughtheRutherford-Bohrplanetarymodeloftheatom.Whatarethepropertiesofanalphaparticle?Forreview,analphaparticleisidenticaltoaheliumnucleushavingtwoprotonsandtwoneutrons.Itisarelativelyheavy,high-energyparticle,withapositivechargeof+2fromitstwoprotons.Alphaparticleshaveavelocityinairofapproximately1/20thespeedoflight,dependingupontheindividualparticle'senergy.Whataretheconditionsthatleadtoalphaparticleemission?Whentheratioofneutrons-to-protonsinthenucleusistoolow,certainatomsrestorethebalancebyemittingalphaparticles.Forexample:Polonium-210has126neutronsand84protons,aratioof1.5-to-1.Followingradioactivedecaybytheemissionofanalphaparticle,theratiobecomes124neutrons-to-82protons,or1.51-to-1.Alpha-emittingatomstendtobeverylargeatoms--thatis,theyhavehighatomicnumbers.Withsomeexceptions,naturallyoccurringalphaemittershaveatomicnumbersofatleast82(theelementlead).

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Whichradionuclidesarealphaemitters?Therearemanyalpha-emittingradioactiveelements,bothnaturalandman-made:AlphaEmitterAtomicNumberAmericium-24195Plutonium-23694Uranium-23892Thorium-23290Radium-22688Radon-22286Polonium-21084Whathappenstoatomsduringalphaemission?Thenucleusisinitiallyinanunstableenergystate.Aninternalchangetakesplaceintheunstablenucleusandanalphaparticleisejected,leavingadecayproduct.Theatomhasthenlosttwoprotonsalongwithtwoneutrons.Thelossofanalphaparticleactuallychangestheatomtoadifferentelement,becausethenumberofprotonsdeterminestheelement.Polonium-210isanalphaemitter.Duringradioactivedecay,itlosestwoprotons,andbecomesaLead-206atom,whichisstableornon-radioactive.

Whatusesdoalphaemittershave?Thepositivechargeofalphaparticlesisusefulinsomeindustrialprocesses:•Radium-226isusedincancertreatmentbyinsertingtinyamountsofradiumintothetumorousmass.•Polonium-210servesasastaticeliminatorinpapermillsandotherindustries.Thealphaparticles,duetotheirpositivecharge,attractlooseelectrons,thusreducingstaticcharge.•SomesmokedetectorsusethealphaemissionsfromAmericium-241tohelpcreateanelectricalcurrent.Thealphaparticlesstrikeairmoleculeswithinachamber,knockingelectronsloose.Theresultingpositivelychargedionsandnegativelychargedelectronscreateacurrentastheyflowbetweenpositivelyandnegativelychargedplateswithinthechamber.Whensmokeparticlesenterthedevice,theyattachtoandinterrupttheflowofchargedparticles,breakingthecurrentandsettingoffthealarm.

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Howdoalphaemittersgetintotheenvironment?Mostalphaemittersoccurnaturallyintheenvironment.Forexample,alphaparticlesaregivenoffbyUranium-238,Radium-226,andothermembersoftheuraniumdecayseries.Thesearepresentinvaryingamountsinnearlyallrocks,soilsandwater.Theopportunityforenvironmentalandhumanexposureincreasegreatlywhensoilsandrockformationsaredisturbedbytheextractionofminerals.Uraniumminingwaste,whichincludesuraniummilltailings,havehighconcentrationsofuraniumandradium.Oncebroughttothesurface,theycouldbecomeairborneandentersurfacewaterasrunoff.

Mining,andcurrentmethodsforprocessingphosphateoreforfertilizer,generatelargepilesor"stacks"ofphosphogypsum,inwhichnaturallyoccurringradiumisconcentrated.

Howdoalphaparticleschangeintheenvironment?Alphaparticlesdon'tgetveryfarintheenvironment.Onceemitted,theytravelrelativelyslowly,atapproximately1/20thespeedoflight,duetotheirelectricchargeandlargemass.Theyloseenergyrapidlyintheair,usuallyexpendingitwithinafewcentimeters.Becausealphaparticlesarenotradioactive,oncetheyhavelosttheirenergy,theypickupfreeelectronsandbecomehelium.Alphaparticlesalsocannotpenetratemostmattertheyencounter.Evenapieceofpaper,orthedeadouterlayersofhumanskin,issufficienttostopalphaparticles.

Howcanalphaparticlesaffectpeople’shealth?Thehealtheffectsofalphaparticlesdependgreatlyuponhowexposuretakesplace.Externalexposure(externaltothebody)isoffarlessconcernthaninternalexposure,becausealphaparticleslacktheenergytopenetratetheouterdeadlayerofskin.However,ifalphaemittershavebeeninhaled,ingested(swallowed)orabsorbedintothebloodstream,sensitivelivingtissuecanbeexposedtoalpharadiation.Theresultingbiologicaldamageincreasestheriskofcancer;inparticular,alpharadiationisknowntocauselungcancerinhumanswhenalphaemittersareinhaled.Thegreatestexposuretoalpharadiationcomesfromtheinhalationofradonanditsdecayproducts,severalofwhichalsoemitpotentalpharadiation.

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BETAPARTICLESBetaparticlesaresub-atomicparticlesejectedfromthenucleusofsomeradioactiveatoms.Theyareequivalenttoelectrons.Thedifferenceisthatbetaparticlesoriginateinthenucleusandelectronsoriginateoutsidethenucleus.Whatarethepropertiesofbetaparticles?Betaparticleshaveanelectricalchargeof-1.Theyhaveamassof549-millionthsofoneatomicmassunit(orAMU),whichisabout1/2,000ofthemassofaprotonorneutron.Thespeedofindividualbetaparticlesdependsonhowmuchenergytheyhave,andvariesoverawiderange.Itistheirexcessenergy,intheformofspeed,thatcausesharmtolivingcells.Whentransferred,thisenergycanbreakchemicalbondsandformions.

Whathappenstobetaparticlesintheenvironment?Betaparticlestravelseveralfeetintheopenairandareeasilystoppedbysolidmaterials.Whenabetaparticlehaslostitsenergy,itislikeanyotherlooseelectron.Whetherintheoutdoorenvironmentorinthebody,theseelectronsarethenpickedupbyapositiveion.

Howarepeopleexposedtobetaparticles?Therearebothnaturalandman-madebeta-emittingradionuclides.Potassium-40andCarbon-14areweakbetaemittersthatarefoundnaturallyinourbodies.Somedecayproductsofradonemitbetaparticles,butitsalpha-emittingdecayproductsposeamuchgreaterhealthrisk.Betaemittersthatejectenergeticparticlescanposeasignificanthealthconcern.Theiruserequiresspecialconsiderationofboththebenefitsandtheirpotentiallyharmfuleffects.•Phosphorus-32andIodine-131aretwobetaemittersusedinmedicalimaging,diagnosticandtreatmentprocedures.Forexample,peoplewhohavetakenradioactiveiodinewillemitbetaparticles.Theymustfollowstrictprocedurestoprotectfamilymembersfromexposure.

•Radioactiveiodinemayentertheenvironmentduringanuclearreactoraccident,potentiallycausingagriculturaldamageandcontamination,andeventuallyfinditswayintothefoodsupply.

•Industrialgaugesandinstrumentscontainingconcentratedbeta-emittingradiation

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sourcescanbelost,stolenorabandoned.Iftheseinstrumentsthenenterthescrapmetalmarket,orsomeonefindsone,thesourcestheycontaincanexposepeopletobetaemitters.

Doesitmatterhowapersonisexposedtobetaparticles?Yes.Directexposuretobetaparticlesishazardousbecauseemissionsfromstrongsourcescanreddenorevenburntheskin.However,emissionsfrominhaledoringestedbetaparticleemittersarethegreaterconcern.Betaparticlesreleaseddirectlyintolivingtissuecancausedamageatthemolecularlevel,whichcandisruptcellfunction.Becausetheyaremuchsmallerandhavelesschargethanalphaparticles,betaparticlesgenerallytravelfurtherintotissues.Asaresult,thecellulardamageismoredispersed.

HealthEffectsofBetaParticlesBetaradiationcancausebothacuteandchronichealtheffects.Acuteexposuresareuncommon.Contactwithastrongbetasourcefromanabandonedindustrialinstrumentisthetypeofcircumstanceinwhichacuteexposurecouldoccur.Chroniceffectsaremuchmorecommon.Chroniceffectsresultfromfairlylow-levelexposuresoveralongperiodoftime.Theydeveloprelativelyslowly,takingfiveto30yearstomanifest.Themainchronichealtheffectfromradiationiscancer.Whenexposureisinternal,betaemitterscancausetissuedamageandincreasetheriskofcancer.Somebeta-emitters,suchasCarbon-14,distributewidelythroughoutthebody.Othersaccumulateinspecificorgansandcausechronicexposures:•Iodine-131concentratesheavilyinthethyroidgland.Itincreasestheriskofthyroidcancerandotherdisorders.•Strontium-90accumulatesinboneandteeth.

GAMMARAYSAgammarayisapacketofelectromagneticenergy--aphoton.Gammaphotonsarethe

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mostenergeticphotonsintheelectromagneticspectrum.Gammaraysorgammaphotonsareemittedfromthenucleusofsomeunstable(radioactive)atoms.

Whodiscoveredgammaradiation?FrenchphysicistHenriBecquereliscreditedwithdiscoveringgammaradiation.In1896,hediscoveredthaturaniummineralscouldexposeaphotographicplatethroughheavyopaquepaper.Thepreviousyear,

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