Natural background radiation - Canadian Nuclear Safety ...

Natural forms of radiation are found in cosmic rays, radioactive soil and rocks, radon. Background radiation is a constant source of ionizing ... Skiptomaincontent Skiptofooter Naturalbackgroundradiation November2020 Factsheet–Naturalbackgroundradiation(PDF) Quickfacts Radiationhasalwaysbeenpresentandisallaroundusinmanynaturalforms.Lifehasevolvedinaworldwithsignificantlevelsofionizingradiation. Manyradioisotopesarenaturallyoccurring,andoriginatedduringtheformationofthesolarsystemandthroughtheinteractionofcosmicrayswithmoleculesintheatmosphere.Tritiumisanexampleofaradioisotopeformedbythisinteraction. Radioisotopessuchaspolonium-210,carbon-14andpotassium-40naturallyoccurwithinthehumanbody. Potassium-40ispresentinmanycommonfoodsincludingredmeats,whitepotatoes,carrots,bananas,limabeansandBrazilnuts. Theannualaverageeffectivedosefromnaturalbackgroundradiationisapproximately1.8millisieverts(mSv)inCanadaand2.4mSvworldwide. Radiationisenergyinmotion,intheformofwavesorstreamsofparticles.Radiationhasalwaysbeenpresentandisallaroundusinmanyforms. Whenpeoplehearthewordradiation,theyoftenthinkofatomicenergy,nuclearpowerandradioactivity,butradiationhasmanydifferentformsandcomesfrommanyothersources.Soundandvisiblelightarefamiliarformsofradiation;othertypesincludeultravioletradiation(thatproducesasuntan),infraredradiation(aformofheatenergy),andradioandtelevisionsignals.Theseareexamplesofnon-ionizingradiation. Ionizingradiationhastheabilitytoknockelectronsoutoforbitaroundatoms,upsettingtheelectron/protonbalanceandpotentiallydamagingcells.Examplesincludealpha,beta,gammaandneutronradiationandx-rays. Lifehasevolvedinaworldwithsignificantlevelsofionizingradiationandourbodieshaveadaptedtoit. Theelectromagneticspectrum Naturalradiationsources Backgroundradiationisaconstantsourceofionizingradiationpresentintheenvironmentandemittedfromavarietyofsources.AccordingtotheUnitedNationsScientificCommitteeontheEffectsofAtomicRadiation(UNSCEAR),therearefourmajorsourcesofnaturalradiation:cosmicradiation,terrestrialradiationandintakesofnaturallyoccurringradionuclidesthroughinhalationandingestion. Cosmicradiation Theearth’souteratmosphereiscontinuallybombardedbycosmicradiation.Usuallyitoriginatesfromavarietyofsources,includingthesunandothercelestialeventsintheuniverse.Someionizingradiationwillpenetratetheearth’satmosphereandbecomeabsorbedbyhumanswhichresultsinnaturalradiationexposure. Terrestrialradiation Thecompositionoftheearth’scrustisamajorsourceofnaturalradiation.Themaincontributorsarenaturaldepositsofuranium,potassiumandthoriumwhich,intheprocessofnaturaldecay,willreleasesmallamountsofionizingradiation.Uraniumandthoriumarefoundessentiallyeverywhere.Tracesofthesemineralsarealsofoundinbuildingmaterialssoexposuretonaturalradiationcanoccurfromindoorsaswellasoutdoors. Inhalation Mostofthevariationinexposuretonaturalradiationresultsfrominhalationofradioactivegasesthatareproducedbyradioactivemineralsfoundinsoilandbedrock.Radonisanodourlessandcolourlessradioactivegasthatisproducedbythedecayofuranium.Thoronisaradioactivegasproducedbythedecayofthorium.Radonandthoronlevelsvaryconsiderablybylocationdependingonthecompositionofsoilandbedrock. Oncereleasedintotheair,thesegaseswillnormallydilutetoharmlesslevelsintheatmospherebutsometimestheybecometrappedandaccumulateinsidebuildingsandareinhaledbyoccupants.Radongasposesahealthrisknotonlytouraniumminers,butalsotohomeownersifitislefttocollectinthehome.Onaverage,itisthelargestsourceofnaturalradiationexposure. Ingestion Traceamountsofradioactivemineralsarenaturallyfoundinthecontentsoffoodanddrinkingwater.Forinstance,vegetablesaretypicallycultivatedinsoilandgroundwaterwhichcontainsradioactiveminerals.Onceingested,thesemineralsresultininternalexposuretonaturalradiation.Someoftheessentialelementsthatmakeupthehumanbody,mainlypotassiumandcarbon,haveradioactiveisotopesthataddsignificantlytoourbackgroundradiationdose. Naturalradiationdoses Effectivedoseisageneraltermthatreferstotheamountofenergyabsorbedbytissuefromionizingradiation.Theeffectivedoseismeasuredinsieverts(Sv)andismorecommonlyexpressedinunitsofeithermillisieverts(mSv)–whichrepresentsathousandthofasievert–ormicrosieverts(μSv)–onemillionthofasievert.Thetotalworldwideaverageeffectivedosefromnaturalradiationisapproximately2.4mSvperyear;inCanada,itis1.8mSv.Insomepartsoftheworld,itisnaturallymuchhigher–forinstanceontheKeralaCoastinIndia,theannualeffectivedoseis12.5mSv.Thedosevarieswiththesourceoftheradiation.Forexample,innorthernIran,geologicalcharacteristicsresultinadosethatcanreach260mSvayear. Dosesfromnaturalbackgroundradiation   Cosmicradiation Regionsathigheraltitudesreceivemorecosmicradiation.AccordingtoastudybyHealthCanada,theannualeffectivedoseofradiationfromcosmicraysinVancouver,BritishColumbia,whichisatsealevel,isabout0.30mSv.ThiscomparestothetopofMountLorne,Yukon,whereat2,000m,apersonwouldreceiveadoseofabout0.84mSvannually.Flyinginanairplaneincreasesexposuretocosmicradiation,resultinginafurtheraveragedoseof0.01mSvperCanadianperyear.     Terrestrialradiation Therearealsonaturalsourcesofradiationintheground,andsomeregionsreceivemoreterrestrialradiationfromsoilsthatcontaingreaterquantitiesofuranium.Theaverageeffectivedosefromtheradiationemittedfromthesoil(andtheconstructionmaterialsthatcomefromtheground)isapproximately0.5mSvperyear.However,thisdosevariesdependingonlocationandgeology,withdosesreachingashighas260mSvinNorthernIranand90mSvinNigeria.InCanada,theestimatedhighestannualdoseforterrestrialradiationisapproximately1.4mSv,asmeasuredintheNorthwestTerritories.     Inhalation Theearth’scrustproducesradongas,whichispresentintheairwebreathe.Radongasnaturallydispersesasitenterstheatmospherefromtheground.However,whenradongasentersabuilding(throughthefloorfromtheground),aconcentrationofittendstobuildup.Long-termexposuretoelevatedlevelsofradonincreasestheriskofdevelopinglungcancer.Theworldwideaverageannualeffectivedoseofradonradiationisapproximately1.2mSv.     Ingestion Anumberofsourcesofnaturalradiationpenetrateourbodiesthroughthefoodweeat,theairwebreatheandthewaterwedrink.Potassium-40isthemainsourceofinternalirradiation(asidefromradondecay)foundinavarietyofeverydayfoods.Theaverageeffectivedosefromthesesourcesisapproximately0.3mSvayear. Worldwidedoselevelsfromnaturalbackgroundradiation Thetotalworldwideaverageeffectivedosefromnaturalradiationisapproximately2.4mSvayear.However,dosescanvarygreatly.ThefollowingfigureshowshowCanadiancitiesandtheCanadianaveragedosecomparetootherpartsoftheworld. Sources:Gratskyetal.2004,UNSCEAR2008,NCRP1602009 Datemodified: 2020-11-24 Secondarymenu Resources Environmentalprotection A-Z Indigenousengagement CNSCSpeakerSeries LearningPortal Canada'snuclearhistory FactSheets Alarmresponseguidelinesforradiationportalmonitoringsystems Canada'shistoricalroleindevelopingnuclearweapons FactSheet:Decommissioningofnuclearpowerplants FactSheet:Depleteduranium:TheCanadianregulator'sperspective FactSheet:Nuclearpowerplantsandsolarflares RegulatingthepackagingandtransportofnuclearsubstancesinCanada Polonium-210 RadioactiveSourcesSafelyUsedinCanadafortheBenefitofallCanadians RadoninCanada'sUraniumIndustry RegulatingRadioactiveWastefromNuclearPowerPlantsinCanada Factsabouttritium UraniumMiningandMilling NaturalBackgroundRadiation Radon CNSChearing:LicenceamendmentforAREVA'sMcCleanLakeoperation RegulatingCanada'sGeologicalRepositories Naturallyoccurringradioactivematerial Householdsmokedetectorsafetyanddisposal ProtectingtheGreatLakesfromRadionuclides GreenhousegasemissionassessmentsfortheCanadiannuclearfuelcycle UnderstandingRadiation OversightofCanada'sFrameworkforRadioactiveWasteManagement FrequentlyAskedQuestions(FAQs) Infographics Mythbusters Videos MapofCNSC-regulatedfacilities Healthstudies Forms Fukushima Internationalcooperation NuclearfacilitiesinCanada Newnuclearprojects NewsRoom Presentations Protocols Publications Radiation ScientificandTechnicalInformation