培訓(xùn)課件X射線熒光分析導(dǎo)論

電(Dian)子波譜1Hz-1kHz

1kHz-1014Hz

1014Hz-1015Hz

1015Hz

-1021Hz

超低頻率電磁波無線電波

微波紅外線可見光

伽馬射線紫外線LowenergyHighenergyX射線

第一頁，共六十六頁。Theory入射X射線轟擊原子的內(nèi)層電子，如果能量大于它的吸收邊，該內(nèi)層電子被驅(qū)逐出整個(gè)原子（整個(gè)原子處(Chu)于高能態(tài)，即激發(fā)態(tài)）。較高能級(jí)的電子躍遷、補(bǔ)充空穴，整個(gè)原子處于低能態(tài)，即基態(tài)。由高能態(tài)轉(zhuǎn)化為低能態(tài)，釋放能量。

ΔE=Eh-El.

能量將以X射線的釋放，產(chǎn)生X射線熒光。第二頁，共六十六頁。TheHardwareSourcesOpticsFilters&TargetsDetectors第三頁，共六十六頁。SourcesEndWindowX-RayTubesSideWindowX-RayTubesRadioisotopesOtherSourcesScanningElectronMicroscopesSynchrotronsPositronandotherparticlebeams 第四頁，共六十六頁。EndWindowX-RayTubeX-rayTubesVoltagedetermineswhichelementscanbeexcited.Morepower=lowerdetectionlimitsAnodeselectiondeterminesoptimalsourceexcitation(applicationspecific).第五頁，共六十六頁。SideWindowX-RayTubeBeWindowSiliconeInsulationGlassEnvelopeFilamentElectronbeamTarget(Ti,Ag,Rh,etc.)CopperAnodeHVLead第六頁，共六十六頁。RadioisotopesIsotopeFe-55Cm-244Cd-109Am-241Co-57Energy(keV)5.914.3,18.322,8859.5122Elements(K-lines)Al–VTi-BrFe-MoRu-ErBa-UElements(L-lines)Br-II-PbYb-PuNonenoneWhileisotopeshavefallenoutoffavortheyarestillusefulformanygaugingapplications.第七頁，共六十六頁。OtherSourcesSeveralotherradiationsourcesarecapableofexcitingmaterialtoproducex-rayfluorescencesuitableformaterialanalysis.ScanningElectronMicroscopes(SEM)–Electronbeamsexcitethesampleandproducex-rays.ManySEM’sareequippedwithanEDXdetectorforperformingelementalanalysisSynchotrons-ThesebrightlightsourcesaresuitableforresearchandverysophisticatedXRFanalysis.

PositronsandotherParticleBeams–Allhighenergyparticlesbeamsionizematerialssuchthattheygiveoffx-rays.PIXEisthemostcommonparticlebeamtechniqueafterSEM.第八頁，共六十六頁。SourceModifiersSeveralDevicesareusedtomodifytheshapeorintensityofthesourcespectrumorthebeamshapeSourceFiltersSecondaryTargetsPolarizingTargetsCollimatorsFocusingOptics第九頁，共六十六頁。SourceFiltersFiltersperformoneoftwofunctionsBackgroundReductionImprovedFluorescenceDetectorX-RaySourceSourceFilter第十頁，共六十六頁。FilterTransmissionCurve%TRANSMITTEDENERGYLowenergyx-raysareabsorbedAbsorptionEdgeX-raysabovetheabsorptionedgeenergyareabsorbedVeryhighenergyx-raysaretransmittedTiCrTitaniumFiltertransmissioncurveThetransmissioncurveshowsthepartsofthesourcespectrumaretransmittedandthosethatareabsorbed第十一頁，共六十六頁。FilterFluorescenceMethodENERGY(keV)TargetpeakWithZnSourcefilterFeRegionContinuumRadiationThefilterfluorescencemethoddecreasesthebackgroundandimprovesthefluorescenceyieldwithoutrequiringhugeamountsofextrapower.第十二頁，共六十六頁。FilterAbsorptionMethodENERGY(keV)TargetpeakWithTiSourcefilterFeRegionContinuumRadiationThefilterabsorptionMethoddecreasesthebackgroundwhilemaintainingsimilarexcitationefficiency.第十三頁，共六十六頁。SecondaryTargetsImprovedFluorescenceandlowerbackground

Thecharacteristicfluorescenceofthecustomlinesourceisusedtoexcitethesample,withthelowestpossiblebackground

intensity.Itrequiresalmost100xthefluxoffiltermethodsbutgivessuperiorresults.第十四頁，共六十六頁。SecondaryTargetsSampleX-RayTubeDetectorSecondaryTargetThex-raytubeexcitesthesecondarytargetTheSecondarytargetfluorescesandexcitesthesampleThedetectordetectsx-raysfromthesample第十五頁，共六十六頁。SecondaryTargetMethodENERGY(keV)TubeTargetpeakWithZnSecondaryTargetFeRegionContinuumRadiationSecondaryTargetsproduceamoremonochromaticsourcepeakwithlowerbackgroundthanwithfilters第十六頁，共六十六頁。SecondaryTargetVsFilterComparisonofoptimizeddirect-filteredexcitationwithsecondarytargetexcitationforminorelementsinNi-200第十七頁，共六十六頁。PolarizingTargetTheoryX-rayarepartiallypolarizedwhenevertheyscatteroffasurfaceIfthesampleandpolarizerareorientedperpendiculartoeachotherandthex-raytubeisnotperpendiculartothetarget,x-raysfromthetubewillnotreachthedetector.TherearethreetypeofPolarizationTargets:BarklaScatteringTargets-Theyscatterallsourceenergiestoreducebackgroundatthedetector.SecondaryTargets-Theyfluorescewhilescatteringthesourcex-raysandperformsimilarlytoothersecondarytargets.DiffractiveTargets-Theyaredesignedtoscatterspecificenergiesmoreefficientlyinordertoproduceastrongerpeakatthatenergy.第十八頁，共六十六頁。CollimatorsCollimatorsareusuallycircularoraslitandrestrictthesizeorshapeofthesourcebeamforexcitingsmallareasineitherEDXRForuXRFinstruments.TheymayrelyoninternalBraggreflectionforimprovedefficiency.SampleTubeCollimatorsizesrangefrom12micronstoseveralmm第十九頁，共六十六頁。FocusingOpticsBecausesimplecollimationblocksunwantedx-raysitisahighlyinefficientmethod.FocusingopticslikepolycapillarydevicesandotherKumakhovlensdevicesweredevelopedsothatthebeamcouldberedirectedandfocusedonasmallspot.Lessthan75umspotsizesareregularlyachieved.SourceDetectorBraggreflectioninsideaCapillary第二十頁，共六十六頁。DetectorsSi(Li)PINDiodeSiliconDriftDetectorsProportionalCountersScintillationDetectors第二十一頁，共六十六頁。DetectorPrinciplesAdetectoriscomposedofanon-conductingorsemi-conductingmaterialbetweentwochargedelectrodes.X-rayradiationionizesthedetectormaterialcausingittobecomeconductive,momentarily.Thenewlyfreedelectronsareacceleratedtowardthedetectoranodetoproduceanoutputpulse.Inionizedsemiconductorproduceselectron-holepairs,thenumberofpairsproducedisproportionaltotheX-rayphotonenergy第二十二頁，共六十六頁。Si(Li)DetectorWindowSi(Li)crystalDewarfilledwithLN2Super-CooledCryostatCooling:LN2orPeltierWindow:BerylliumorPolymerCountsRates:3,000–50,000cpsResolution:120-170eVatMnK-alphaFETPre-Amplifier第二十三頁，共六十六頁。Si(Li)CrossSection第二十四頁，共六十六頁。PINDiodeDetectorCooling:Thermoelectricallycooled(Peltier)Window:BerylliumCountRates:3,000–20,000cpsResolution:170-240eVatMnk-alpha第二十五頁，共六十六頁。SiliconDriftDetector-SDD

Packaging:SimilartoPINDetector

Cooling:PeltierCountRates;10,000–300,000cps

Resolution:140-180eVatMnK-alpha第二十六頁，共六十六頁。ProportionalCounterAnodeFilamentFillGases:Neon,Argon,Xenon,KryptonPressure:0.5-2ATMWindows:BeorPolymerSealedorGasFlowVersionsCountRatesEDX:10,000-40,000cpsWDX:1,000,000+Resolution:500-1000+eVWindow第二十七頁，共六十六頁。ScintillationDetectorPMT(Photo-multipliertube)SodiumIodideDiskElectronicsConnectorWindow:BeorAlCountRates:10,000to1,000,000+cpsResolution:>1000eV第二十八頁，共六十六頁。SpectralComparison-AuSi(Li)Detector10vs.14KaratSiPINDiodeDetector10vs.14Karat第二十九頁，共六十六頁。PolymerDetectorWindowsOptionalthinpolymerwindowscompared toastandardberylliumwindowsAffords10ximprovementintheMDLforsodium(Na)第三十頁，共六十六頁。DetectorFiltersFiltersarepositionedbetweenthesampleanddetectorinsomeEDXRFandNDXRFsystemstofilteroutunwantedx-raypeaks.SampleDetectorX-RaySourceDetectorFilter第三十一頁，共六十六頁。DetectorFilterTransmission%TRANSMITTEDENERGYLowenergyx-raysareabsorbedEOIistransmittedAbsorptionEdgeX-raysabovetheabsorptionedgeenergyareabsorbedVeryhighenergyx-raysaretransmittedSClAniobiumfilterabsorbsClandotherhigherenergysourcex-rayswhilelettingSx-rayspass.Adetectorfiltercansignificantlyimprovedetectionlimits.NiobiumFilterTransmissionandAbsorption第三十二頁，共六十六頁。FilterVs.NoFilterUnfilteredTubetarget,Cl,andArInterferencePeakDetectorfilterscandramaticallyimprovetheelementofinterestintensity,whiledecreasingthebackground,butrequires4-10timesmoresourceflux.Theyarebestusedwithlargeareadetectorsthatnormallydonotrequiremuchpower.第三十三頁，共六十六頁。RossVs.HullFiltersThepreviousslidewasanexampleoftheHullorsimplefiltermethod.TheRossmethodillustratedhereforClanalysisusesintensitiesthroughtwofilters,onetransmitting,oneabsorbing,andthedifferenceiscorrelatedtoconcentration.ThisisanNDXRFmethodsincedetectorresolutionisnotimportant.第三十四頁，共六十六頁。WavelengthDispersiveXRFWavelengthDispersiveXRFreliesonadiffractivedevicesuchascrystalormultilayertoisolateapeak,sincethediffractedwavelengthismuchmoreintensethanotherwavelengthsthatscatterofthedevice.

SampleDetectorX-RaySourceDiffractionDeviceCollimators第三十五頁，共六十六頁。DiffractionThetwomostcommondiffractiondevicesusedinWDXinstrumentsarethecrystalandmultilayer.Bothworkaccordingtothefollowingformula.nl=2d′sinqn=integerd=crystallatticeormultilayerspacingq=Theincidentangle=wavelengthAtoms第三十六頁，共六十六頁。MultilayersWhilethecrystalspacingisbasedonthenaturalatomicspacingatagivenorientationthemultilayerusesaseriesofthinfilmlayersofdissimilarelementstodothesamething.Modernmultilayersaremoreefficientthancrystalsandcanbeoptimizedforspecificelements.OftenusedforlowZelements.第三十七頁，共六十六頁。SollerCollimatorsSollerandsimilartypesofcollimatorsareusedtopreventbeamdivergence.TheareusedinWDXRFtorestricttheanglesthatareallowedtostrikethediffractiondevice,thusimprovingtheeffectiveresolution.SampleCrystal第三十八頁，共六十六頁。CoolingandTemperatureControlThediffractiontechniqueisrelativelyinefficientandWDXdetectorscanoperateatmuchhighercountrates,soWDXInstrumentsaretypicallyoperatedatmuchhigherpowerthandirectexcitationEDXRFsystems.Diffractiondevicesarealsotemperaturesensitive.

ManyWDXRFInstrumentsuse:X-RayTubeCoolers,andThermostaticallycontrolledinstrumentcoolers第三十九頁，共六十六頁。ChamberAtmosphereSampleandhardwarechambersofanyXRFinstrumentmaybefilledwithair,butbecauseairabsorbslowenergyx-raysfromelementsparticularlybelowCa,Z=20,andArgonsometimesinterfereswithmeasurementspurgesareoftenused.Thetwomostcommonpurgemethodsare: Vacuum-Forusewithsolidsorpressedpellets Helium-Forusewithliquidsorpowderedmaterials第四十頁，共六十六頁。ChangersandSpinnersOthercommonlyavailablesamplehandlingfeaturesaresamplechangersorspinners.AutomaticsamplechangersareusuallyofthecircularorXYZstagevarietyandmayhavehold6to100+samplesSampleSpinnersareusedtoaverageoutsurfacefeaturesandparticlesizeaffectspossiblyoveralargertotalsurfacearea.

第四十一頁，共六十六頁。TypicalPINDetectorInstrumentThisconfigurationismostcommonlyusedinhigherendbenchtopEDXRFInstruments.第四十二頁，共六十六頁。TypicalSi(Li)DetectorInstrumentThishasbeenhistoricallythemostcommonlaboratorygradeEDXRFconfiguration.第四十三頁，共六十六頁。EnergyDispersiveElectronicsFluorescencegeneratesacurrentinthedetector.InadetectorintendedforenergydispersiveXRF,theheightofthepulseproducedisproportionaltotheenergyoftherespectiveincomingX-ray.DETECTORSignaltoElectronicsElementAElementCElementBElementD第四十四頁，共六十六頁。Multi-ChannelAnalyserDetectorcurrentpulsesaretranslatedintocounts(countspersecond,“CPS”).PulsesaresegregatedintochannelsaccordingtoenergyviatheMCA(Multi-ChannelAnalyser).SignalfromDetectorChannels,EnergyIntensity(#ofCPSperChannel)第四十五頁，共六十六頁。WDXRFPulseProcessingTheWDXmethodusesthediffractiondeviceandcollimatorstoobtaingoodresolution,soThedetectordoesnotneedtobecapableofenergydiscrimination.Thissimplifiesthepulseprocessing.Italsomeansthatspectralprocessingissimplifiedsinceintensitysubtractionisfundamentallyanexerciseinbackgroundsubtraction.Note:Someenergydiscriminationisusefulsinceitallowsforrejectionoflowenergynoiseandpulsesfromunwantedhigherenergyx-rays.

第四十六頁，共六十六頁。EvaluatingSpectraK&LSpectralPeaksRayleighScatterPeaksComptonScatterPeaksEscapePeaksSumPeaksBremstrahlungInadditiontoelementalpeaks,otherpeaksappearinthespectra:第四十七頁，共六十六頁。K&LSpectralLinesK-alphalines:

Lshelle-transitiontofillvacancyinKshell.Mostfrequenttransition,hencemostintensepeak.

K-betalines:

Mshelle-transitionstofillvacancyinKshell.LShellKShell

L-alphalines:

Mshelle-transitiontofillvacancyinLshell.

L-betalines:

Nshelle-transitiontofillvacancyinLshell.KalphaKbetaMShellLalphaNShellLbeta第四十八頁，共六十六頁。K&LSpectralPeaksRhX-rayTubeL-linesK-Lines第四十九頁，共六十六頁。ScatterSomeofthesourceX-raysstrikethesampleandarescatteredbackatthedetector.

Sometimescalled “backscatter”SampleSourceDetector第五十頁，共六十六頁。RayleighScatterX-raysfromtheX-raytubeortargetstrikeatomwithoutpromotingfluorescence.Energyisnotlostincollision.(EI=EO)Theyappearasasourcepeakinspectra.AKA-“Elastic”ScatterEIEORhX-rayTube第五十一頁，共六十六頁。ComptonScatterX-raysfromtheX-raytubeortargetstrikeatomwithoutpromotingfluorescence.Energyislostincollision.(EI>EO)Comptonscatterappearsasasourcepeakinspectra,slightlylessinenergythanRayleighScatter.AKA-“Inelastic”ScatterEIEORhX-rayTube第五十二頁，共六十六頁。SumPeaks2photonsstrikethedetectoratthesametime.Thefluorescenceiscapturedbythedetector,recognizedas1photontwiceitsnormalenergy.Apeakappearsinspectra,at:2X(ElementkeV).第五十三頁，共六十六頁。EscapePeaksX-raysstrikethesampleandpromoteelementalfluorescence.SomeSifluorescenceatthesurfaceofthedetectorescapes,andisnotcollectedbythedetector.Theresultisapeakthatappearsinspectrum,at:ElementkeV-SikeV(1.74keV).RhX-rayTube1.74keV第五十四頁，共六十六頁。BrehmstrahlungBrehmstrahlung(orContinuum)Radiation:

Germanfor“breakingradiation”,noisethatappearsinthespectraduetodecelerationofelectronsastheystriketheanodeoftheX-raytube.第五十五頁，共六十六頁。InterferencesSpectralInterferencesEnvironmentalInterferencesMatrixInterferences第五十六頁，共六十六頁。SpectralInterferencesSpectralinterferencesarepeaksinthespectrumthatoverlapthespectralpeak(regionofinterest)oftheelementtobeanalyzed.Examples:K&LlineOverlap-S&Mo,Cl&Rh,As&PbAdjacentElementOverlap-Al&Si,S&Cl,K&Ca...Resolutionofdetectordeterminesextentofoverlap.220eVResolution140eV

ResolutionAdjacentElementOverlap第五十七頁，共六十六頁。EnvironmentalInterferencesLightelements(Na-Cl)emitweakX-rays,easilyattenuatedbyair.Solution:PurgeinstrumentwithHe(lessdensethanair=lessattenuation).Evacuateairfromanalysischamberviaavacuumpump.EitherofthesesolutionsalsoeliminateinterferencefromAr(spectraloverlaptoCl).Argon(Ar)isacomponentofair.AirEnvironmentHeEnvironmentAlAnalyzedwithSiTarget第五十八頁，共六十六頁。MatrixInterferencesAbsorption:

Anyelementcanabsorborscatterthefluorescenceoftheelementofinterest.Enhancement:

Characteristicx-raysofoneelementexciteanotherelementinthesample,enhancingitssignal.InfluenceCoefficients,sometimescalledalphacorrectionsareusedtomathematicallycorrectforMatrixInterferencesAbsorption/EnhancementEffects第五十九頁，共六十六頁。Absorption-EnhancementAffectsIncomingsourceX-rayfluorescesFe.FefluorescenceissufficientinenergytofluoresceCa.Caisdetected,Feisnot.Responseisproportionaltoconcentrationsofeachelement.Red

=Fe,absorbedBlue

=Ca,enhancedSource

X-rayX-RayCapturedbythedetector.Sample第六十頁，共六十六頁。SoftwareQualitativeAnalysisSemi-QuantitativeAnalysis(SLFP,NBS-GSC.)QuantitativeAnalysis(MultipleintensityExtractionandRegressionmethods)第六十一頁，共六十六頁。QualitativeScanPeakIDThisspectrumalsocontraststheresolutionofaPINdiodedetectorwithaproportionalcountertoillustratetheimportanceofdetectorresolutionwithregardtoqualitativeanalysis.AutomatedPeakidentificationprogramsareausefulqualitativeexaminationtool

ElementTags第六十二頁，共六十六頁。Semi-QuantitativeAnalysisThealgorithmcomputesboththeintensitytoconcentrationrelationshipandtheabsorptionaffectsResultsaretypicallywithin10-20%ofactualvalues.SLFPStandardlessFundamentalParametersFP(withStandards)NBS-GSC,NRLXRF,Uni-Quant,TurboQuant,etc…Theconcentrationto