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1 A111D7l^ . 'wasestablishedbyanactotCongressonMarch3 , 'soverallgoalistostrengthenandadvancethe Nation' ,theBureauconductsresearchandprovides:(1 )abasisfortheNation'sphysicalmeasurement system,(2)scientificandtechnologicalserv icesforindustryandgovernment,(3)atechnic albasisforequityintrade,and(4) 'stechnicalworkisper-formedbytheNational MeasurementLaboratory,theNationalEnginee ringLaboratory, ;coordinatesthesystemwithmeasurementsyst emsofothernationsandfurnishesessentialse rvicesleadingtoaccurateanduniformphysica landchemicalmeasurementthroughouttheNati on'sscientificcommunity,industry,andcomm erce;conductsmaterialsresearchleadingtoi mprovedmethodsofmeasurement,standards,an ddataonthepropertiesofmaterialsneededbyi ndustry,commerce,educationalinstitutions ,andGovernment;providesadvisoryandresear chservicestootherGovernmentagencies;deve lops,produces,anddistributesStandardRefe renceMaterials; :AbsolutePhysicalQuantities-^ RadiationResearch ChemicalPhysics AnalyticalChemistry MaterialsScienceTHENATIONALENGINEERINGLA BORATORY providestechnologyandtechnicalser-vicest othepublicandprivatesectorstoaddressnati onalneedsandtosolvenationalproblems;cond uctsresearchinengineeringandappliedscien ceinsupportoftheseefforts;buildsandmaint ainscompetenceinthenecessarydisciplinesr equiredtocarryoutthisresearchandtechnica lservice;developsengineeringdataandmeasu rementcapabilities;providesengineering-m easurementtraceabilityservices;developst estmethodsandproposesengineeringstandard sandcodechanges;developsandproposesnewen gineeringpractices.

2 :AppliedMathematics ElectronicsandElectricalEngineering^ ManufacturingEngineering BuildingTechnology FireResearch ChemicalEngineering^THEINSTITUTEFORCOMPU TERSCIENCESANDTECHNOLOGY conductsresearchandprovidesscientificand technicalservicestoaidFederalagenciesint heselection,acquisition,application,andu seofcomputertechnologytoimproveeffective nessandeconomyinGovernmentoperationsinac cordancewithPublicLaw89-306( ),relevantExecutiveOrders,andotherdirect ives;carriesoutthismissionbymanagingtheF ederalInformationProcessingStandardsProg ram,developingFederalADPstandardsguideli nes,andmanagingFederalparticipationinADP voluntarystandardizationactivities;provi desscientificandtechnologicaladvisoryser vicesandassistancetoFederalagencies; :ProgrammingScienceandTechnology ComputerSystemsEngineering.'Headquarters andLaboratoriesatGaithersburg,MD,unlesso therwisenoted;mailingaddressWashington,D C20234.'Somedivisionswithinthecenterarel ocatedatBoulder, > ^ ( ,DC20234 , ,MalcolmBaldrige,SecretaryNATIONALBUREAU OFSTANDARDS,ErnestAmbler,DirectorIssuedM ay1982 ( ), ,35pages(May1982)CODEN: , , , ,andinparticular, ,DivisionofOoerationalSafety,DOE, :thechoiceofneutronsource;phantomconstru ction;fluencetodoseeouivalentconversion; andcorrectionsforairscatter,roomreturn, ,semi-empirical,analyticexpressionsaregi venfortheroomreturncorrection, :airscatter;calibration;californium;dose equivalent;dosimeter;neutron;rerrmeter; ; , ,wewillgenerallyrefertodosimetercalibrat ions,butmostoftheproceduresapplyequallyw elltoactiveinstruments, ,itisaverysimpleprocedure:thedosimeteris placedataconvenientdistancefromaneutrons ourceofknownemissionrate, ,thedistance,andthetime, *conversionfactor, , ,dividedbythecorrectedreading,isthenthed osimetercalibrationfactorforthatsource.)

3 * (Sv).1Sv=1 Jkg"^= ,however,isnotingeneraluseinDOElaborator ies, ,toavoidconfusion,weshalluserem(ormillir em) ,itwouldseemtobeneedlesspedantrytorefert othewell-known9-inchsphericalremmeterasa " "1 Ingeneral,tfiereareseveralpossiblewaysof performingeachofthesesteps, "correct"procedures; ,however,thateveryoneusethesameprocedure ,sothatdosimetercalibrationswillbeafunct iononlyofthedosimetertypeandthesourceene rgyspectrum, , ^proposesfourneutronsources:D^O-QrOOCOO/ ll9/11moderatedCf,Cf,Am-B, ,Pu-Li,andAm-Li,althoughthesesourcesmayn olongerbegenerallyavailablefromsuppliers ..Leavingaside,forthemoment,themoderated californiumsource, :theneutronspectrum,whichissimilarto2352 34thatfromUfission,hasbeencarefullyevalu atedandisverywellknown;''sourcesareavail ableinanyreasonablestrength,arephysicall ysmall'(approachingapointsource)andrelat ivelylightlyencapsulated;theneutronemiss ionisclosetoisotropic; ( ),which, , (andthewearer)areexpectedtobeexposed.

4 (Notethatinthisreport"moderated252califo rnium"willalwaysrefertoaCfsourceinthecen terofaD^Osphereof15cmradius,^ "thickcadmium).Forcalibratingalbedodosim eters,particularlyiftheyaretobeusedinthe relativelysoftspectrafoundinreactorenvir onments, ^thatforothercommondosimetertypes(film,C R-39,polycarbonate)therearenotverygreatd ifferences(lessthanafactorof2) ,themoderatedCfisthemoreversatileofthetw osources, (HPSSC),"CriteriaforTestingPersonnelDosi metryPerformance."Ontheotherhand,ifworke rsareexposedprimarilytoneutronswithfissi onenergy(orhigherenergy), , , + ,(la)foremission69ratesbetween^10 ,thesourceshouldbeplacedat,ornear, , , ,followingtheHPSSCD raftStandard,werecommendthatalldosimeter sbeirradiatedona fphantom.'-'8,,, WhileHankinsfoundnodifferenceinalbedodos imeterreadingsforirradiationsusingphanto msofpolyethelene,Lucite(poly(methylmetha crylate)),orwater, (CH2=C(CH2)C00CH2)iscloserinchemicalcomp ositiontotissuethaniswater.

5 (Inaddition,aLucitephantomislesslikelyto becomeapuddleonthefloor.)''.gHankinsfoun d,however,thatalbedodosimeterreadingsdid dependonthe9 shapeofthephantom,andNashandJohnsonshowe dthatthereadingswouldoetoolowifthedosime terwereplacedtooclosetoiheedgeofthephant omface.:Topermitsimultaneousirradiations ofseveraldosimeters,theHPSSCD raftStandardthereforespecifiesthatthepha ntombearectangularparallelepiped,40cmX40 cmX15cmthick(ratherthantheearlierspecifi ed30cmx30cmx15cm) ,butitmaybeundulyconservative,sincetheex peri-910mentalevidence'indicatesthatthe" edgeeffect"isdeterminedonlybytheposition ofthesensitiveelementinthealbedodosimete r( ,theTLDchipitself)."* ,existingphantomsofwaterorpolyethelene,n osmallerthan30cmx30cmx15cm,maybeused, ,evenona" ,thephantomshouldbeplacedonalowmassstand forminimumscattering, :first,betweenwhattwopointsisthedistance tobemeasured;and,second,isthereanoptimum (or,atleast,apreferred)valueforthisdista nce?

6 ,thesensitiveelementsshouldbeontheperiph eryofacirclecenteredonthefaceofthephanto m,sothatthedosimetersareallequidistantfr omthesource.(Thefaceofthephantomshould,o fcourse,beperpendiculartothelinejoiningt hesourceandphantomcenters.)Ifthisisnotpo ssible, ,bare, ,IngandCross^^haveshownthatthecenterofth esphereisalsotheappropriatemeasuringpoin t,( )fordistancesgreaterthan30cm(onespheredi ameter).Measuringtothefrontfaceofthephan tomissimplyaconvention, ,however,partofthealbedosystem, "effective"depthissometimes15definedasth epointinthephantomsuchthat,whendistancei smeasuredto21213thatpoint,theresponsefol lowsthe1 'whichareconsistentwithaneffectivedeptho f1to3cmforalbedodosimetersirradiatedwith aCfsource, ,thecalibrationfactorcouldbecorrectedtow hatitwouldbeatgreatdistances; , ,therewillthusbesomeambiguityinthecalibr ations, (especiallyforalbedodosimeters)aswellas, possibly, ,theHPSSCD raftStandardrecommendsa50cmsource-to-pha ntomdistance,andwesuggestthatthisrecomme ndationbefollowed.

7 ^Forasphericaldetector( ,Bonnersphere,sphericalremmeter)anda1415 pointneutronsource,AxtonandHarrisonhaves hownthatoneshouldagainmeasuretothecenter ofthesphere,butthattheeffectivefluenceis increasedbyafactorofapproximately[1+(r/d )'^/6],whereristheradiusofthesphere, ,forasource-detectorspacingequaltothedia meterofthesphere,r/d= "Bonnersphere,a50cmspacingwouldmaketheco rrectionalmostcompletelynegligible(11/2% ).ForanAndersson-Braunremmeter,wehavefou ndthattheinversesquarelawisobeyeddowntod =35cm,wherethelongaxisoftheremmeterisper pendiculartothelinebetweenthesourceandth ecenteroftheremmeter, , '252 ForcalculationsinvolvingthebareCfspectru m,werecommendthe23 Grundl-Eisenhauerspectrumevaluation.'Thi sevaluationseemstobegenerallyacceptedbyt hecommunityofcaliforniumusers,andcalcula tionsbasedonthisspectrum(inareassuchasre actormaterialsdosimetry)navegenerallygiv enexcellentagreementwithmeasuredvalues." '^TheevaluatedspectrumisgivenintheAppend ix, '''ofthemoderatedCfspectrumgivesresultsw hichareinsubstantialagreementwiththeir19 /7calculation.

8 '''' "recommended"setsoffluencetodoseequivale ntconversionfactorshasbeendulynoted,andd eplored,in181920theliterature.''Theposit ionwithintheDOEcommunitywasgiven21byHank insin1977, , ,however,givevalueswhicnaremoreconsisten twiththeICRP recommendations(whichspecifylog-loginter polation) ,andtheICRP recommendations, , ( ) (ortheChilton)values,becausewedonotfeelt hatitisappropriateatthistimetointroducey etanothersetof'recommended" ,theGrundl-EisenhauerCfspectrum,andthe19 81 IngandCrossspectrumformoderatedcaliforni um,werecommendthefollowingconversionfact ors:252 Bare"^^^Cf:-52 DoseEquivalentConversion= ;_5 DoseEquivalentRate=^'^^^l""^ x3600r-32= ^^^Cf:-6 DoseEquivalentConversion= ";qoYin~^?DoseEquivalentRate= ,whereQisthebaresourceemissionrate,inneu trons/secondristhesource-detectordistanc eincentimeters,asdefinedin s4.( ,11%lossofneutronswhicharemoderatedinthe D^Otobelowthecadmiumcut-off.) ,duetotheuncertaintyinthespectrumshape, \-{Ic).}

9 Thus,theuncertaintyinthedoseequivalentra tev; , ,thedoseequivalentconversionisnotasensit ivefunctionofthespectralshape,thelackofe xperimentalconfirmationoftheshapeleadsus torecommendthatan252uncertaintyof7', ,sothatdividingthesourceemissionrateby4- rgivesthefluxdensityatthedosimeter, ,werefertothesequantitiesasthe"freefield fluxdensity"andthe"freefielddoseequivale ntrate,"respectively,andtheirtimeintegra lsasthe"freefieldfluence"and"freefielddo seequivalent."Thatis, ,airscatteringgenerallyamountstoonlyafew percent, , ,thecontributionofroom-reflectedneutrons totheresponseofthedosimetermaybesignific ant, ,theymustnotbeconsideredaproperpartofthe calibrationfield,butshouldratfierbeconsi deredatypeofbackground, :thecalibrationfactorshouldbeauniqueprop ertyofthedosimetertypeandtheneutronsourc espectrum, ,allcali-brationsshouldrefertothe"freefi eld"quantities,sothatcalibrationsofthesa medosimeteratdifferentlaboratorieswillgi vethesameresult, , , , ,itoffersphysicalinsightintotheproblemwi thout,inmanycases, , ,however, ,listedinTableI,arederivedfromMcCall'sai r2730 , '^ ,wewilltreatthequantities"fluence"and"do seequivalent" ,PolycarbonateTrackEtchDosimeterDoseEqui valent9"SphericalRemmeterAlbedoDosimeter Fluence3"SphereDetectorreadingsshouldbed ecreasedbythesepercentagestoobtainfree-f ieldvalues, ^^^CfModerated"^^^ ,ceilingandfloor,or"roomreturn,"isnotane wproblem, , ,orinaroomwith,say, cos6R^a00(^r^I2(1))

10 WhereR^/R^istherelativeresponseofthedete ctortothereflectedandthesourceneutrons,a ISthealbedoofthereflectingsurface,gisafa ctortoaccountforanisotropicdetectorrespo nse,andarethespectrum-averagedresponsesf orthereflectedandsourceneutrons,respecti vely,risthesource-to-detectordistance,th especularangle6isgivenbytan6=r/2h;and=(2 h)^+r'^.Forr<h,eq(1)simplifiestoRa2rarr/o\0oh(ThevalueofR^/Rqcalculatedfromeq(1)differsfromthatobtainedfromeq(2)bylessthan4%forh>3r.)12 Forepi-cacimiurnneutrons, ,decreasingby20% ^/a^ , ^r0^go/a^r0 TypeofResponseBareCfModeratedCfNTAFilm, " " (1)or(2) ,considera3"sphereandmoderatedcaliforniu msource, ,eq(1)predictsR^^/R^= ; , (1)hasnotbeenexplicitlyverifedexperiment ally, ,thatofacompletelyenclosedconcreteroom, ,but,ontheaverage,eachneutronmakes32^21 ,'^^'^andhenceonlytheresultswillbepresen tedhere.(Averysimiliardevelop-35menthada lsobeengivenearlierbySavinskiiandhilyush kin.)Ithasbeenshownthattheroomscatteredn eutronsareessentiallyuniformlydistribute dthroughouttheroom,andthatforbarecalifor niuminaconcreteroom:Ran = R00c2r_r(3)with4-^r^=ZA.