fukushima nuclear disaster - japan radiation poisioning

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Radiation safety expert Andrew Karam has written for Popular Mechanics aboutwhat went wrong at Fukushima and how Japan reacted to the emergency. Now he'sjust back from a trip to Japan, where he took radiation detectors to assess thecontamination levels himself. Not all radiation measurements are created equal, soKaram walks us through what the numbers, and the different radiation units, reallymean.

What Those Fukushima Radiation Counts ReallyMean: Analysis

MAY 10, 2011



By Andrew Karam



Yoshikazu Tsuno/AFP/Getty Images



AsanyonewhofollowsthecrisisattheFukushimanuclearplantknows,therehavebeenanumberofradiationstatistics,expressedinvariousunits,comingfromdifferentsourcesincludingorganizationsliketheInternationalAtomicEnergyAgency(IAEA),whichreleasedregularupdatesofradiationlevels.TheIAEAmadeitclearthatlevelsfurtherawayfromthereactorsitearenotdangerouslyhigh,butasascientistandaformerNavynuclearpowertechnician,Iwascurioustolearnmorefirsthand.SoIwenttoJapan,whereItraveledwithinabout12milesofthereactors,andspentnearlytwoweekstakingmyownmeasurementsusingseveraldifferenttools.

Whenitcomestohumanhealth,radiationsafetyprofessionalsareconcernedwithmorethanjustoverallradiationoutput.First,wecareaboutradiationdose:theamountofradioactiveenergydepositedinanobjectorperson.ThisismeasuredinradsintheU.S.andinGraysintheSIunitsystem.

Secondly,weworryaboutthekindofradiation.Justasabowlingballcausesmoredamagethanatennisball,sometypesofradiation(alphaparticlesorneutrons,forexample)causemorebiologicaldamagethanothers(suchasbetaorgammaradiation).Themoredangeroustypesofradiationhaveahigherrelativebiologicaleffectiveness(RBE)level.Theunitofmeasurecalledremormillirem(orSievertinSIunits),whichyou'veprobablyheardmentionedduring

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coverageofFukushima,takesRBEintoaccount.Therefore,remmeasuresnotjustradiationdose,butalsothebiologicalharmthatradiationcancause.Mostradiationworkersarelimitedto2000millirem(mrem)peryearandupto25,000mremduringemergencieswebegintoseeradiationsicknessat100,000mrem.Bycomparison,mostofusreceiveabout300mremannuallyfromnaturalradiation,andasinglewholebodyCTscanwillgiveusabout2000mrem.IntheareasofJapanIvisited,radiationdoserateswereelevatedtoaboutthreetofourtimestypicalnaturalradiationdoserates(whichareabout.1mremperhour),butnowherenearashighasnaturalradiationlevelsI'vemeasuredinpartsofIran.

Finally,radiationexpertsalsosurveyhowmuchradioactivecontaminationapersonorobjecthasreceived,measuredincountsperminute(cpm)orindecaysperminute(dpm).(Contaminationiswhenradioactivityappearswhereit'snotwantedsortoflikedust.)Despitethedoomandgloomassociatedwiththeterminpopularparlance,however,whatradiationsafetyexpertsarereferringtowhenwesay"contamination"israrelyharmful.Becauseit'sameasureofhowmuchradiationhadaccumulatedonyou,itgoesdownwhenyoucleanup.IthinkofitlikechangingadiaperIdon'twanttogetcontaminated,butifIdo,Ijustwashitoffandgoonwithmyday.Japaneseofficialsaresurveyingpeopleleavingtheaffectedareas,andanyonewithmorethan100,000cpmofcontaminationisaskedtochangeclothes(whichremovesupto90percentofthecontamination)andpossiblytoshower.Assoonastheircontaminationlevelsarebelowthisnumber,they'reapprovedtogo.

Sowithallthesedifferentkindsofdata,whatgeardoyouneedtomaketherightmeasurements?Therearetwofundamentaltypesofradiationinstrumentsthosethatmeasureonlythenumberoftimesradiationinteractswiththedetector,andthosethatmeasuretheamountofenergydeposited.TheGeigerMuellertube(theGeigercounter),probablythemostwidelyknownradiationinstrument,fallsintothefirstcategory.Geigercounterscanmeasurealpha,betaandgammaradiation,makingthemthemostversatilekindofradiationdetector,buttheyaretypicallyusedto



measurecontaminationonly.That'sbecauseanormalGeigercountercan'tdistinguishbetweenhighandlowenergyradiationeverythinglooksthesametoit.It'slikeholdingahandfulofrocks,pebblesandgrainsofsandandsimplycountingeveryobject:Asinglegrainofsandcountsthesameasarock,eventhoughweknowthatrocksarelargerandweighmore.SoGeigercountersaregreatformeasuringcontamination,butnotsogreatatmeasuringradiationdoserate,thebiologicalpartoftheequation.

Gettingattheradiationdoseraterequiresmeasuringtheamountofenergydepositedbytheradiationand,therefore,requiresdifferentequipment.Anionchambermeasurestheenergydepositedinamassofairbymeasuringtheamountofelectricalcharge(whichisrelatedtoionization)thatoccursinthechamber.Ionizationchamberscandirectlymeasureradiationdoseratetoafairlyhighdegreeofaccuracy.

Anotherwaytomeasureradiationdoserateistouseadevicecalledascintillationcounteradetectorthatusesacrystal,suchassodiumiodide.Whenradiationinteractswiththecrystal,thecrystalemitslight,andtheamountoflightemittedisproportionaltotheenergydepositedinthecrystal(theradiationdose).Scintillationdetectorscanmeasurebothcountrate(contamination)anddoserate.Thedrawbackisthatscintillationcounterscanusuallymeasureonlyonetypeofradiation(alpha,betaor,inthecaseofsodiumiodide,gamma).Buttheymeasureitverywell.AndthoughGeigercountersaren'tintendedforradiationdoseratemeasurements,theycandoitinspecialcircumstancesiftheotherdetectorsaren'tavailable.OnekindofGeigercountercalledanenergycompensatedGMadjustsfordifferentenergiesofradiation.Ifoneofthoseisnotaround,aconversionchartcancorrectwhattheGeigercountersaystowhatthedoseratereallyis.

InJapanIhadanumberofinstrumentswithme.Oneisatypeofscintillationcounterthat'ssetuptoidentifyspecificradionuclidesbymeasuringtheenergyofthegammarayphotonsitseesaprocesscalledgammaspectroscopy.ThiswayIwasabletoidentifylonglastingisotopesofcesium,likeCs134andCs137,thatcamefromFukushima.Butnearlyalloftheradioactiveiodinewhichhadbeenaconcernearlyonhasdecayedawaybynow,soIcouldnotdetectanyofit.IhadapressurizedionchambertomeasureradiationdoserateatthelowlevelsofexposuredetectedinJapan.IalsocarriedaregularionchamberandanenergycompensatedGMincasedoseratesbecomehigherthanwhatthepressurizedionchamberwillread,butwewerenotexposedtoanylevelofradiationhighenoughto



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needeitherone.(Mytotalradiationexposure12milliremisalmostentirelyduetoairtravel.)Finally,I'vealwaysgotmyInstadoseadevicethatIcanplugintomylaptopcomputertoreadmydosedirectly.Ihavetoadmit,carryingalloftheseinstrumentsaroundstartedtowearonmyshoulder(andexplainingthemtoairportsecuritywasachallenge).Buttheinformationtheyprovideisinterestingenoughtomakethebotherworthwhile.

AndrewKaramhasover30yearsofexperienceinhealthphysics(radiationsafety),beginningwithaneightyearstintasamechanicaloperatorandradiationsafetyspecialistintheNavy.Sincethen,KaramhasworkedfortheStateofOhio,theOhioStateUniversity,theUniversityofRochesterandasaprivateconsultant.Heistheauthoroffivebooksandanupcomingeightpartseries,ControversiesinScience.HecurrentlylivesinNewYorkCity,whereheworksonissuesrelatedtoourresponsetoradiologicalandnuclearemergencies.Checkouthiswebsite.

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What Do You Think?Addacomment8comments

JohnDiponzioThankyou!ReplyLikeFollowPostMarch24,2014at10:55am

FredrickMboma TopCommenterIimportusedcarsfromJapan.Myquestionsare:

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1.Docarstrap(iebecomecontaminatedby)nuclearradiationfromFukushima?2.Ifyes,forhowlongcansuchradiationstayincars,andinwhatparts?3.Whatwouldbethebestwayanddevice(s)tomeasureit?

IhavenotedRussiahasbannedsomecarsduetoradiationcontamination.Thenewsisherehttp://rt.com/news/japanrussiafukushimacars201/ReplyLikeFollowPostMarch4,2014at1:52pm

SteveBowerGraceDavisHighSchoolThankyouReplyLikeFollowPostJanuary10,2014at6:28am

CenaLombardiRobertoMassimo TopCommenterUniversitDiTorinoThereminoGeiger&MCAkits.

Youcanbuildorbuyasensibleandcheap#thereminoGeigerorMCAhwkit.Lookathttp://www.theremino.com/contacts/pricelist.

The#theremino#radioactivitymoduleshavemillivoltripple.LookattheelusivePotassiumK40inthegammaspectrumhttp://www.theremino.com/blog/gammaspectrometry/images.

Thanksforyourattention,RobertoCena

TheThereminoteam.ReplyLike FollowPostFebruary15,2013at6:22pm1

FredrickMboma TopCommenterIimportusedcarsfromJapan.Myquestionsare:

1.Docarstrap(iebecomecontaminatedby)nuclearradiationfromFukushima?2.Ifyes,forhowlongcansuchradiationstayincars,andinwhatparts?3.Whatwouldbethebestwayanddevice(s)tomeasureit?

IhavenotedRussiahasbannedsomecarsduetoradiationcontamination.Thenewsisherehttp://rt.com/news/japanrussiafukushimacars201/ReplyLikeMarch4,2014at1:53pm

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