DOC

Numerical

By Sam Watkins,2014-07-24 00:41
16 views 0
NumericalNumeri

    Numerical

OUJiwei.

    ;ElectronicsDepartment,ElectronicEngineeringInstitute,Hefei230038,China ;lDepartmentofModernPhysics,UniversityofScienceandTechnologyofChina.Hefei230o26.China

    ;DepartmentofScientificResearch,ElectronicEngineeringInstitute,Hefei230038,China ;AbstractDuetotheirlowcost,flexibility,andconvenienceforlongdistancedatatransfer,plasticscintillationfibers

    ;(PSF)havebeenincreasinglyusedinbuildingdetectorsorsensorsfordetectingvariousradiationsandimaging.Inthis

    ;paper,GEANT4MonteCarlosimulationtoolwasusedtoobtainsomeradiationeffectsofPSFunderhighenergy

    ;neutronirradiation.BCF

    20,aplasticfibermaterial,producedbySaintGobaln,wasusedinthesimulation.Thefiber

    ;consistsofacorescintillatingmaterialofpolystyreneandanacrylicoutercladding.Incidentneutronsproduceenergy

    ;depositioninfiberthroughneutroninducedrecoilprotonevents.Therelationshipsbetweenenergydeposition

    ;efficiencyandfiberlength,fiberradiusandincidentneutronenergyarepresented.Thevariationwiththoseparameters

    ;andparameterselectionarealsoanalyzed.

    ;KeywordsRadiationeffect,Highenergyneutron,Scintillationfiber

    ;CLCnumberTL91

    ;1Introduction

    ;Xrayradiographyandthermalneutron

    ;radiographyhavebeenusedsuccessfullyinnon

    ;destructiveexamination(NDE)ofvariousmaterials.

    ;However,thetechniquesareseverelyhandicappedby

    ;theirlimitationtorelativelythinobjects.Fastneutron

    ;radiographycaninspectmuchthickerobjects,

    ;includingcomposites,ceramics,orrubberIn

    ;particular,itisidealforobjectscomposedof

    ;hydrogen-richmaterials,whereitisdifficultto

    ;acquirehighqualityimageswiththermalneutronand

    ;Xrayradiographytz.

    ;AsX-rays,electromagneticradiationsofshort

    ;wavelengths.interacttllorbitelectronsofanatom,

    ;theerosSsectionoftheinteractionincreaseswiththe

    ;atomicnumberoftheatom.Neutronsarenotthecase.

    ;Theyinteractwitl1theneutronsandprotonsofa

    ;nucleus.Generally,neutronspenetratematerialseasily, ;butsomematerialsareexceptionstothisruleandcan ;SupportedbyNationalNaturalScienceFoundation(No.60602065) ;Correspondingauthor.E-mailaddress:qinglima@gmail.corn ;Reeeiveddate:2o08.o4.25

    ;beimagedreadily.Atpresent,fewneutronimaging ;detectorsprovidehighquantumefficiencyforfast ;neutrons.Mostexistingdetectorsweredevelopedfor ;neutronradiographywithcollimatedthermalneutron ;beamssuchas,scintillator+CCDcamera,imaging

    ;plates,amorphoussimeonflatpanel,andCMOSpixel ;detector4.Thefirstisthemostpopulardetectorfor ;fastneutronradiography.

    ;Aninteresting

    ;developmentisthescintillatingfibert8-12

    ;,which

    ;possesseshighefficiencyoffastneutroncapture,good ;positionresolution,lowcost,andthepossibilityof ;largeareadetectors.

    ;Inordertolearngeneralcharacteristicsofthe ;scintillationfiber,therelationshipsbetweenenergy ;depositionefficiencyandfiberlength,fiberradiusand ;incidentneutronenergywerestudiedthroughGEANT4 ;simulationinthisarticle.Variationsoftheparameters ;andparameterselectionareanalyzed.Theresultsmay ;beusefulfortheparameterselectioninpractice. ;

    ;No.4MAQinglieta1./NumericalsimulationofhighenergyneuWonradiationeffectofscintillationfiber237

    ;2Scint.1latiOnfibers

    ;Inrecentyears,theplasticscintillationfiber(PSF) ;hasbeenappliedinmanyfields,suchasneutron ;imaging,particlediscrimination,calorimeters,etc[13.. ;ThemainadvantagesofPSFareitsfastresponse, ;flexibilityandelectromagneticimmunity[18.

    ;Mostcommonavailablescintillationfibersare ;madeofeitherpolymersorsilicaglasses.The ;materialsareusuallydopedwithceriumorterbiumto ;improvetheirphotoelectricabsorption[19.Forneutron

    ;detection,wedonotexpectthatthetwokindsof ;materialswoulddiffersignificantly.Therefore, ;BCF20,acommonplasticscintillationfiber,was ;chosenforoursimulation.Theresultsshouldbe ;applicabletoothertypesofPSFs.Thecoreof

    ;BCF-20fiberismadeofpolystyrene(PS)dopedwith ;1%butylphenylbyphenylyloxadiazole(PBD).The ;refractiveindexanddensityofthefiberare1.60and ;1.05g-cm,respectively.PurePShasanemission ;spectrumin300-350nm,whichisnotsuitableto ;commonphotodetectors.Itisthereforenecessaryto ;dopePSwithabout1%ofsomeprimaryfluortoreach ;ascintillationefficiencyofabouthalfofthatof ;crystallineanthraceneandwithabout0.01%of ;secondaryfluortoshiftthelightemittedbythe ;primaryfluortotheregionofmaximumsensitivityof ;theabsorptionregionofthephoto.detector[18.The

    ;claddingmaterialOfBCF.20fiberisPMMA

    ;(polymethylmethacrylate)andhasrefractiveindexof ;1.49.Thethicknessofthecladdinglayerisabout3% ;ofcorediameter.Thecalculatednumericalapertureof ;thefiberis0.58,thetrappingefficiencyis3.44%,the ;numberofemissionlightperMeVisabout8000 ;photons,theemissionspectrumispeakedat492nm, ;andthedecaytimeis2.7ns,accordingtothe ;manufacturer[.ThefiberstructureisshowninFig.1. ;Fig.1Structureofthefiber

    ;crOSSsection

    ;3Computersimulation

    ;Thesimulationwascarriedoutusinga

    ;Monte.Carlocode.GEANT4[l2l1.

    ;whichisatoolkit

    ;packagedevelopedattheEuropeanOrganizationfor ;NuclearResearch(CERNf_orsimulatingthe ;performanceofdetectorsusedinnuclearandhigh ;energyphysics.Ithasbeenusedinmanyother ;applications,suchasfluiddynamicsandmedical ;physics.Ittracesthetrajectoriesofparticlesandtheir ;interactionswiththematerials.Theresultsobtained ;withGE4areconsistentwiththoseobtained ;usingotherprograms[-.

    ;ThemaindatadrivenmodelsinGEANT4deal

    ;withneutronandprotoninducedisotopeproduction, ;andwiththedetailedtransportofneutronsatlow ;energies(upto20MeV).Theinteractionsofneutrons ;intheenergyrangearedividedintofourparts ;analogoustotheotherhadronicprocessesinGE4 ;WleconsideredradiationcaDture,elasticscattering, ;fissionandinelasticscatteringasseparatemodels….

    ;Thesemodelscomplywiththeinterfaceforusewith ;theGEANT4hadronicprocesseswhichenabletheir ;transparentusewithintheGE4too1.kittogether ;withallotherGEANT4complianthadronicshower ;models.A11cross.sectiondataaretakenfromthe ;ENDF/B.VIevaluateddatalibrary.Alowenergy ;limitforparticleinteractionisdefinedcorresponding ;totheminimalenergywithinthevalidityrangeofthe

    .Userscanalternativelydefineahigher ;modelt20

    ;thresholdforanyspecificapplication.

    ;Itisimportantforustoknowthefiber’sradiation

    ;eectOffastneutrons.Thegeometricalstructureof ;detectorinthesimulationisgiveninFig.2.witha ;planeneutronsourceplacedacrossthecenterofthe ;fiber,10cmaway,whichisnotpresentinthefigure. ;Theneutronsourcehasthesameareaasthecross ;sectionofthefiber.Thesimulationcoversarelative ;broadenergyrangefortheincomingneutrons,from10 ;keVtoabout10MeV.

    ;Fig.2Geometricalstructureofthedetector ;

    ;238NUCLEARSCIENCEANDTECHNIQUESVbI.19 ;Asanimportantparameterofaneutronimaging ;detector,good-eventrate(GER)isdefinedasthe ;probabilityforanincidentphotontogenerateagood ;eventinthefiber,i.e.theratioofinteractedphoton ;numbertot0talnumberofincidentphotons.The ;simulatedGERversusfiberlengtIlandneutronenergy ;areplottedinFig.3andFig.4.AsCanbeseen,except ;for14MeVneutrons.tIleGERvarieslittlewitIlfibers ;inlengthsofmorethan10cm.Andlittlechangein ;GERisseenwitIlneutronsof<1MeV.However,it ;fallsrapidlywhentheenergyexceeds1M-eV11.1isis ;0fhelpforselectingappropriateneutronenergyto ;achievegreaterefficiency.

    ;1.0

    ;0.8

    ;0.6

    ;0.4

    ;0.2

    ;0.0

    ;Fiberlength/cm

    ;Hg.3Thegood-eventrate.fiberlengthforneutronsof ;differentenergies.

;Neutronenergy/keY

    ;Hg.4Thegood-eventrateofneutronsatdifferentenergies ;4.2Relationshipbetweenenergydeposition ;efficiencyandfiberlength

    ;TheenergydepositionofneutronsinafiberCan ;becharacterizedbyanenergydepositionefficiency ;(EDE),whichisdefinedastheratiooftheenergy ;deposi~dinthefibertotheincidentneutron ;energy.ThesimulatedresultsaregiveninFig.5. ;InFig.5a,forlowenergyneutrons(5500keV),the

    ;depositionefficiencyreachessaturationatthefiber ;lengthofabout6cm.Forhigherenergyneutrons ;(2-14MeV)inFig.5b,wheretheenergydeposition ;efficiencyislowerthanthelowenergyneutrons,the ;EDEincreasesslowlywiththefiberlength.For14 ;MeVneutrons.theefficiencyisabout12%wimafiber ;of10cminlength,andl7.5%witha20cmfiber.In ;viewoftheaboveresults,a10cmfiberwaschosenfor ;thefollowingsimulations.

    ;.

    ;}E

    ;?

    ;C

    ;.9

    ;‘a

    ;?

    ;

    ;Fiberlength/cm

    ;Fiberlength/c

    ;Fig.5Energydepositionefficiency.fiberlengthfor ;neutronsofdifferentenergies.

    ;8lBJIu>a-pc,00

    ;?:8??

    ;000000000

    ;c?石晤?co?o?BJ?c

    ;ac?,?.8,

    ;

    ;No.4MAQinglieta1./Numericalsimulationofhighenergyneutronradiationeffectofscintillationfiber239

    ;4.3RelationshipbetweenEDEandfiberradius ;Fiberradiusisallimportantparameterforgood ;imagequality.Itcannotbetoosmall(causingtoolow ;EDE,orpoorimagecontrast),nortoobig(with ;increasedpixelsize,ordecreasedspatialresolution).

    ;Ontheotherhand,themechanismthatcausesthe ;saturationdescribedabovecouldbetheleakageofthe ;secondaryparticlesproducedbyincidentneutrons. ;Therefore,wesimulatedtheEDEforneutronsof ;givenenergiesinasinglefiberofdifferentdiameters. ;SomeoftheresultsareplottedinFig.6.Ascanbeseen,

    energyneutrons(50keVto2MeV),theEDE ;forlow

    ;ishighenoughtoachievegoodimagecontrast, ;however,theEDEislowforhighenergyneutrons

    ;(higherthan7.5MeV),whichisonlylessthan0.25. ;Therefore,thereshouldbeseverecrosstalkeffectsfor

    ;thosehighenergyneutrons.Ontheotherhand,forthe ;neutronshigherthan7MeV,theEDEincreasesslowly ;withmeradiusfrom0.5mitttO50nllTt.With7.5MeV ;incidentneutrons,theefficiencyisabout0.2,O.23, ;0.32,forradiusof0.5mm,l0mm,and50miI1, ;respectively,thatis,19millincreasedpixel(2double ;9.5mm)correspondingtoonly0.03improvementof ;EDE,whichisnotdeserved.Asaresult.tobalanceme ;EDEandpixelsize,weselecta0.5millradiusinthe ;followingsimulation.

    ;Fiber-adjus/mm

    ;Fig.6Energydepositionefficiencyvs.fiberradiusfor ;neutronsofdifferentenergies.

    ;4.4RelationshipbetweenEDEandincident

    ;neutronenergy

    ;TheEDEinPSFdiffersgreatlyforincident

    ;neutronsofdifferentenergies.Inpractice,theneutron ;energycanbeadjustedtoachieveanexcellent ;efciency.TheEDEsfor10keV20MeVneutrons

    ;bombardingafiberof1m/nx10cmaregiveninFig.7 ;TheEDEdecreasesslowlywimenergyforneutronsof ;l3MeV,andfasterforneutronsof>3MevII1 ;practice,weshouldchooseappropriateneutronenergy ;inthisregard.

    ;Neutronenergy/keV

    ;5000100001500020000

    ;Neutronenergy/keV

    ;Fig.7Energydepositionefficiencyofneutronsof<5MeV(a) ;and5MeV09).

    ;5Conclusions

    ;Asanexcellentnondestructiveevaluation

    ;method,fastneutronradiographyattractsmoreand ;moreinterestsintheworld.Duetoitslowcost,

    ;flexibility.andconvenienceforlongdistancedata ;transfer,especiallybigreactioncrosssectionwith

    ;neutrons,PSFhasbeenwidelyusedinbuilding ;detectorsorsensorsfordetectingneutrons.Radiation ;effectsofPSFunderhigh.energyneutronirradiation ;areobtainedthroughGEANT4simulationtoo1.Itwas ;foundthatthegood.eventratevarieslittlewhenthe

    ?co;?oQ?D?c>0c?百芒?co?o?D>?c ;>0c?0|l

    ;>uc?.lI?co?oQ?DLc

    ;

    ;NUCLEARSCIENCEANDTECHNIQUESV_01.19

    ;fiberlengthismorethan10cm,henceanappropriate ;fiberlengthof10cm,andtheenergydeposition ;efficiencyincreaseswiththefiberradiusandlengtl1. ;Thepresentresultsareoftheoreticsignificancein ;selectingreasonablefiberlengthandincidentneutron ;energyforfutureexperiments.

    ;2

    ;3

    ;4

    ;5

    ;6

    ;7

    ;8

    ;9

    ;11

    ;KimKS,KlannRT,RajuBB,NuclInstrMethPhysRes ;1999,422:929.932.

    ;LehrnannEH.LectureNotesinPhysics,2006,694: ;231.249.

    ;CluzeauS,HuetJ,LetourneurP.NuclInstrMethPhys ;ResB,1994,89:432-436.

    ;LehmannEH,VontobelP,FrciG,eta1.NuclInstrMeth ;PhysResA,2Oo4,531:228-237.

    ;MikerovV.Waschkows~W.NuclInstrMethPhysRes ;A,1999,424:48.52.

    ;MikerovVI,ZhimikIA,BarmakovJN,eta1.Appl ;RadiatIsotop,2004,61:529-535.

    ;LehmarmE,FreiG’NordlundA,eta1.IEEETransNucl

    ;Sci,20o5,52:389-393.

    ;RessD,LercheRA,ElHsRJ,a1.ProceedingsofSPIE ;

    ;1nheInternationalSocietyforOpticalEngineering,1994, ;2281:95-l12.

    ;ZhangQ,WangQ,Xiez,eta1.NuclInstrMethPhysRes ;20o2,486:708.715.

    ;RessD,LercheRA,E1lisRJ,eta1.RevSciInstr,1995, ;66:4943-4948.

    FujineS,YonedaK,YoshiiK,eta1.NuclInstrMethPhys ;

    ;ResA.1999,424:19O.199.

    ;NasseriMM,Yz,W_uX,a1.Nucl1.nstrumMethods ;PhysResB,2OO4,225:617-622.

    ;TangSB,MaQL,Y.mZJ,a1.ApplRadiatIsotop, ;20o8.66:162.167.

    ;14TangS,MaQ,FangJ,eta1.IEEETransNuclSci,2007, ;54:17731778.

    ;15TangSB,YinZJ,MaQL,eta1.NuclInstrumMethods ;PhysResA,20o3,5o6:2503o3B,2Oo7,263:441.445.

    ;16MengeshaWMascarenhasN,PeelJ’eta1.IEEENudear

    ;ScienceSymposiumConferenceRecord——Nuclear

    ;ScienceSymposiumandMedicalImagingConference, ;20o5.535.539.

    ;17MengeshaWMascarenhasN,PeelJ,eta1.ProceeAingsof ;SPIE1nheInternationalSocietyforOpticalEngineering. ;20o5,5923:1-8.

    ;18WhiteTO.NuclInstrumMethodsPhysResA,2003,506: ;25O-303A.1988.273:820.825.

    ;19BicronCorporationwebsite,2003.http:#www.bieron. ;

    ;c

    ;o——

    ;m

    ;.

    ;20AgostinelliS,AllisonJ,AmakoK,eta1.NuclInstrum ;MethodsPhysResA,2003,506:250-303.

    ;21AllisonJ,AmakoK,ApostolakisJ,eta1.IEEETransNucl ;Sd.20D6.53:270.278.

    ;22CarrierJEArchambaultL,BeaufieuL.MedPhys,2004, ;31:484.492.

    ;23AsoKimuraA,TanakaS,eta1.IEEETransNuclSci, ;2005,52:896.901.

    ;24AmakoK,GuatelliS,Ivanchenckoeta1.NuclPhysB- ;ProcSuppl,20o6,150:44-49.

    ;25AmakoK,GuatelliS,IvanchenckoVN,eta1.IEEETrans ;NuclSci,20o5,52:910.918.

    ;26GEANT4PhysicsReferenceManua1.http://geant4.. ;web.cem.ch/geant4.

    ;27TuliJ.EvaluatedNuclearStructureDataFile.

;BNLNCS.51655-Rev87.1987.

    ;28KnollGF.Radiationdetectionandmeasurement.New ;York:JohnWiley&Sons.1979.

    ;29LeroyC.Principleofradiationinteractioninmatterand ;detection.Singapore:WorldScientificPubfication,2004. ;

    ;

Report this document

For any questions or suggestions please email
cust-service@docsford.com