培训课件-X射线荧光分析导论

IntroductiontoXRFLearnXRF.comX射线荧光分析导论IntroductiontoXRFLearnXRF.com电子波谱1Hz-1kHz1kHz-1014Hz1014Hz-1015Hz1015Hz-1021Hz超低频率电磁波无线电波微波红外线可见光伽马射线紫外线LowenergyHighenergyX射线IntroductiontoXRFLearnXRF.comTheory入射X射线轰击原子的内层电子，如果能量大于它的吸收边，该内层电子被驱逐出整个原子（整个原子处于高能态，即激发态）。较高能级的电子跃迁、补充空穴，整个原子处于低能态，即基态。由高能态转化为低能态，释放能量。ΔE=Eh-El.能量将以X射线的释放，产生X射线荧光。IntroductiontoXRFLearnXRF.comTheHardware•Sources•Optics•Filters&Targets•DetectorsIntroductiontoXRFLearnXRF.comSources•EndWindowX-RayTubes•SideWindowX-RayTubes•Radioisotopes•OtherSources–ScanningElectronMicroscopes–Synchrotrons–PositronandotherparticlebeamsIntroductiontoXRFLearnXRF.comEndWindowX-RayTube•X-rayTubes–Voltagedetermineswhichelementscanbeexcited.–Morepower=lowerdetectionlimits–Anodeselectiondeterminesoptimalsourceexcitation(applicationspecific).IntroductiontoXRFLearnXRF.comSideWindowX-RayTubeBeWindowSiliconeInsulationGlassEnvelopeFilamentElectronbeamTarget(Ti,Ag,Rh,etc.)CopperAnodeHVLeadIntroductiontoXRFLearnXRF.comRadioisotopesIsotopeFe-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-PuNonenoneWhileisotopeshavefallenoutoffavortheyarestillusefulformanygaugingapplications.IntroductiontoXRFLearnXRF.comOtherSourcesSeveralotherradiationsourcesarecapableofexcitingmaterialtoproducex-rayfluorescencesuitableformaterialanalysis.ScanningElectronMicroscopes(SEM)–Electronbeamsexcitethesampleandproducex-rays.ManySEM’sareequippedwithanEDXdetectorforperformingelementalanalysisSynchotrons-ThesebrightlightsourcesaresuitableforresearchandverysophisticatedXRFanalysis.PositronsandotherParticleBeams–Allhighenergyparticlesbeamsionizematerialssuchthattheygiveoffx-rays.PIXEisthemostcommonparticlebeamtechniqueafterSEM.IntroductiontoXRFLearnXRF.comSourceModifiersSeveralDevicesareusedtomodifytheshapeorintensityofthesourcespectrumorthebeamshapeSourceFiltersSecondaryTargetsPolarizingTargetsCollimatorsFocusingOpticsIntroductiontoXRFLearnXRF.comSourceFiltersFiltersperformoneoftwofunctions–BackgroundReduction–ImprovedFluorescenceDetectorX-RaySourceSourceFilterIntroductiontoXRFLearnXRF.comFilterTransmissionCurve%TRANSMITTEDENERGYLowenergyx-raysareabsorbedAbsorptionEdgeX-raysabovetheabsorptionedgeenergyareabsorbedVeryhighenergyx-raysaretransmittedTiCrTitaniumFiltertransmissioncurveThetransmissioncurveshowsthepartsofthesourcespectrumaretransmittedandthosethatareabsorbedIntroductiontoXRFLearnXRF.comFilterFluorescenceMethodENERGY(keV)TargetpeakWithZnSourcefilterFeRegionContinuumRadiationThefilterfluorescencemethoddecreasesthebackgroundandimprovesthefluorescenceyieldwithoutrequiringhugeamountsofextrapower.IntroductiontoXRFLearnXRF.comFilterAbsorptionMethodENERGY(keV)TargetpeakWithTiSourcefilterFeRegionContinuumRadiationThefilterabsorptionMethoddecreasesthebackgroundwhilemaintainingsimilarexcitationefficiency.IntroductiontoXRFLearnXRF.comSecondaryTargetsImprovedFluorescenceandlowerbackgroundThecharacteristicfluorescenceofthecustomlinesourceisusedtoexcitethesample,withthelowestpossiblebackgroundintensity.Itrequiresalmost100xthefluxoffiltermethodsbutgivessuperiorresults.IntroductiontoXRFLearnXRF.comSecondaryTargetsSampleX-RayTubeDetectorSecondaryTargetA.Thex-raytubeexcitesthesecondarytargetB.TheSecondarytargetfluorescesandexcitesthesampleC.Thedetectordetectsx-raysfromthesampleIntroductiontoXRFLearnXRF.comSecondaryTargetMethodENERGY(keV)TubeTargetpeakWithZnSecondaryTargetFeRegionContinuumRadiationSecondaryTargetsproduceamoremonochromaticsourcepeakwithlowerbackgroundthanwithfiltersIntroductiontoXRFLearnXRF.comSecondaryTargetVsFilterComparisonofoptimizeddirect-filteredexcitationwithsecondarytargetexcitationforminorelementsinNi-200IntroductiontoXRFLearnXRF.comPolarizingTargetTheorya)X-rayarepartiallypolarizedwhenevertheyscatteroffasurfaceb)Ifthesampleandpolarizerareorientedperpendiculartoeachotherandthex-raytubeisnotperpendiculartothetarget,x-raysfromthetubewillnotreachthedetector.c)TherearethreetypeofPolarizationTargets:–BarklaScatteringTargets-Theyscatterallsourceenergiestoreducebackgroundatthedetector.–SecondaryTargets-Theyfluorescewhilescatteringthesourcex-raysandperformsimilarlytoothersecondarytargets.–DiffractiveTargets-Theyaredesignedtoscatterspecificenergiesmoreefficientlyinordertoproduceastrongerpeakatthatenergy.IntroductiontoXRFLearnXRF.comCollimatorsCollimatorsareusuallycircularoraslitandrestrictthesizeorshapeofthesourcebeamforexcitingsmallareasineitherEDXRForuXRFinstruments.TheymayrelyoninternalBraggreflectionforimprovedefficiency.SampleTubeCollimatorsizesrangefrom12micronstoseveralmmIntroductiontoXRFLearnXRF.comFocusingOpticsBecausesimplecollimationblocksunwantedx-raysitisahighlyinefficientmethod.FocusingopticslikepolycapillarydevicesandotherKumakhovlensdevicesweredevelopedsothatthebeamcouldberedirectedandfocusedonasmallspot.Lessthan75umspotsizesareregularlyachieved.SourceDetectorBraggreflectioninsideaCapillaryIntroductiontoXRFLearnXRF.comDetectors•Si(Li)•PINDiode•SiliconDriftDetectors•ProportionalCounters•Scintilla