Applications of x ray fluorescence.ppt

applicationsofxrayfluorescence,rajkiran,introduction,whenmaterialsareexposedtoshort-wavelengthx-raysortogammarays,ionisationoftheircomponentatomsmaytakeplace.ionisationconsistsoftheejectionofoneormoreelectronsfromtheatom,andmaytakeplaceiftheatomisexposedtoradiationwithanenergygreaterthanitsionisationpotential.x-raysandgammarayscanbeenergeticenoughtoexpeltightlyheldelectronsfromtheinnerorbitalsoftheatom.theremovalofanelectroninthiswayrenderstheelectronicstructureoftheatomunstable,andelectronsinhigherorbitalsfallintothelowerorbitaltofilltheholeleftbehind.infalling,energyisreleasedintheformofaphoton,theenergyofwhichisequaltotheenergydifferenceofthetwoorbitalsinvolved.,introduction,thus,thematerialemitsradiation,whichhasenergycharacteristicoftheatomspresent.thetermfluorescenceisappliedtophenomenainwhichtheabsorptionofradiationofaspecificenergyresultsinthere-emissionofradiationofadifferentenergy(generallylower).,introdution,applications,chemicalanalysis:-theuseofaprimaryx-raybeamtoexcitefluorescentradiationfromthesamplewasfirstproposedbyglockerandschreiberin1928.today,themethodisusedasanon-destructiveanalyticaltechnique,andasaprocesscontroltoolinmanyextractiveandprocessingindustries.inprinciple,thelightestelementthatcanbeanalysedisberyllium(z=4),butduetoinstrumentallimitationsandlowx-rayyieldsforthelightelements,itisoftendifficulttoquantifyelementslighterthansodium(z=11),unlessbackgroundcorrectionsandverycomprehensiveinterelementcorrectionsaremade.,applications,x-rayfluorescenceisusedinawiderangeofapplications,includingresearchinigneous,sedimentary,andmetamorphicpetrologysoilsurveysmining(e.g.,measuringthegradeofore)cementproductionceramicandglassmanufacturingmetallurgy(e.g.,qualitycontrol)environmentalstudies(e.g.,analysesofparticulatematteronairfilters)petroleumindustry(e.g.,sulfurcontentofcrudeoilsandpetroleumproducts)fieldanalysisingeologicalandenvironmentalstudies(usingportable,hand-heldxrfspectrometers),applications,strengthsx-rayfluorescenceisparticularlywell-suitedforinvestigationsthatinvolvebulkchemicalanalysesofmajorelements(si,ti,al,fe,mn,mg,ca,na,k,p)inrockandsedimentbulkchemicalanalysesoftraceelements(inabundances1ppm;ba,ce,co,cr,cu,ga,la,nb,ni,rb,sc,sr,rh,u,v,y,zr,zn)inrockandsediment-detectionlimitsfortraceelementsaretypicallyontheorderofafewpartspermillion,applications,limitationsintheorythexrfhastheabilitytodetectx-rayemissionfromvirtuallyallelements,dependingonthewavelengthandintensityofincidentx-rays.however.inpractice,mostcommerciallyavailableinstrumentsareverylimitedintheirabilitytopreciselyandaccuratelymeasuretheabundancesofelementswithz11inmostnaturalearthmaterials.xrfanalysescannotdistinguishvariationsamongisotopesofanelement,sotheseanalysesareroutinelydonewithotherinstruments.xrfanalysescannotdistinguishionsofthesameelementindifferentvalencestates,sotheseanalysesofrocksandmineralsaredonewithtechniquessuchaswetchemicalanalysis.,typesofxrf,applicationsofxrfisofwiderangeandthesearedevelopedasdifferenttypesofxrfinstrumentsareinvented.therearedifferenttypesofxrfinstrumentsthataredevelopedandeachtypeofinstrumenthasdifferentfunctionandservesdifferentpurpose.typesofxrf:-edxrfwdxrfndxrftxrf,wavelengthdispersivespectrometry,inwavelengthdispersivespectrometers(wdxorwds),thephotonsareseparatedbydiffractiononasinglecrystalbeforebeingdetected.althoughwavelengthdispersivespectrometersareoccasionallyusedtoscanawiderangeofwavelengths,producingaspectrumplotasineds,theyareusuallysetuptomakemeasurementsonlyatthewavelengthoftheemissionlinesoftheelementsofinterest.wavelengthdispersivex-rayfluorescence(wdxrf)istheoldtimeramongcommercialx-rayspectrometers,sincethemethodworkswithouthigh-resolutionsolid-statedetectors.wdxspectrometerswithsimpleelectroniccountingcircuitswerearoundwellbeforethecomputerage,andarestilltheworkhouseandleadingperformerforroutinexrfanalysis,wavelengthdispersivespectrometry,wdxrfcanberelativelysimpleandinexpensive,orcomplexandveryexpensivedependingonthenumberofopticalcomponents.wdxinstrumentsuseax-raytubesourcetodirectlyexcitethesample.becausetheoverallefficiencyofthewdxrfsystemislow,x-raytubesinlargersystemsarenormallyratedat1-4kilowatts.therearesomespecializedlowpowersystemsthatoperateat50to200watts.adiffractiondevice,usuallyacrystalormultilayer,ispositionedtodiffractx-raysfromthesampletowardthedetector.diffractedwavelengthsarethosethatsatisfythe2dsinrelationship,wheredistheatomicspacingwithinthecrystal,andthetaistheanglebetweenthesampleanddetector.otherwavelengthsarescatteredveryinefficiently.collimatorsarenormallyusedtolimittheangularspreadofx-rays,tofurtherimprovetheeffectiveresolutionofthewdxsystem.becausethedetectorisnotreliedonforthesystemsresolutionitcanbeaproportionalcounterorotherlow-resolutioncountercapableofdetectingamillionormorecountspersecond.,wavelengthdispersivespectrometry,applications;-wdxrfcanbeusedforatremendousvarietyofelementalanalysisapplications.itcanbeusedtomeasurevirtuallyeveryelementformnatopuintheperiodictable,andsomeinstrumentscanbeusedforquantitativeorsemi-quantitativeworkforevenlighterelements.itcanmeasureelementalconcentrationsrangingfromafewppmtonearly100percent.itcanbeusedformonitoringmajorcomponentsinaproductorprocessortheadditionofminoradditives.wdxrfisextremelypopularinthegeologicalfieldandisoftenusedformeasuringrawminerals,andfinishedproductscomposedofminerals.,energydispersivex-rayfluorescence,edxrfisrelativelysimpleandinexpensivecomparedtoothertechniques.itrequiresandx-raysource,whichinmostlaboratoryinstrumentsisa50to60kv50-300wx-raytube.lowercostbenchtoporhandheldmodelsmayuseradioisotopessuchasfe-55,cd-109,cm-244,am-241ofco-57orasmallx-raytube.thesecondmajorcomponentisthedetector,whichmustbedesignedtoproduceelectricalpulsesthatvarywiththeenergyoftheincidentx-rays.mostlaboratoryedxrfinstrumentsstilluseliquidnitrogenorpeltiercooledsi(li)detectors,whilebenchtopinstrumentsusuallyhaveproportionalcounters,ornewerpeltiercooledpindiodedetectors,buthistoricallysodiumiodide(nai)detectorswerecommon.somehandhelddeviceuseotherdetectorssuchasmercuriciodide,cdte,andcdznteinadditiontopindiodedevicesdependinglargelyonthex-rayenergyoftheelementsofinterest.themostrecentandfastestgrowingdetectortechnologyisthepeltiercooledsilicondriftdetector(sdd),whichareavailableinsomelaboratorygradeedxrfinstruments.,energydispersivex-rayfluorescence,applications:-edxrfcanbeusedforatremendousvarietyofelementalanalysisapplications.itcanbeusedtomeasurevirtuallyeveryelementformnatopuintheperiodictable,inconcentrationsrangingfromafewppmtonearly100percent.itcanbeusedformonitoringmajorcomponentsinaproductorprocessortheadditionofminoradditive.becausexrfspopularityinthegeologicalfield,edxrfinstrumentsareoftenusedalongsidewdxrfinstrumentsformeasuringmajorandminorcomponentsingeologicalsample.,nondispersivex-rayfluorescence(ndxrf),non-dispersivex-rayfluorescence(ndxrf)gotitsstartinthe1920swhenrossandotherexperimentersdiscoveredthattheycouldisolateanx-raylineforanelementbyusingtwofiltersmadeofdifferentelementsovertwodetectors.onefilterabsorbstheelementsx-rays,whiletheothertransmitsthem.thedifferenceincountsbetweenthetwomatcheddetectorswithbalancedfiltersisthenetintensityandisrelatedtothatelementsconcentration.whencombinedwithearlierworkthatdemonstratedthatelementscouldbemeasuredbymeasuringtotalx-rayintensitiesfromsomesimplesamples,anewandpowerfulmethodwasborn.unfortunatelyitwasalmost50yearslaterwhensmallmicroprocessorbasedanalyzerswerebuiltinthe1970sthatndxrfstartedtomakeacommercialimpact.,nondispersivex-rayfluorescence(ndxrf),ndxrfhastheleastexpensivehardwareofanyofthexrfmethods,becauseitonlyrequiresafewlowcostscomponents.itneedsanx-raysource,usuallyeitheraradioisotopesuchasfe-55,cd-109,cm-244,am-241ofco-57,orasmallx-raytube.anditrequiresadetectorsuchasanionizationchamberorgeiger-muellercounter,whichdoesnotneedtobeenergydispersive.whilerossusedtwodetectors,themorecommonapproachistouseasingledetectoranduseafilterwheelortraytopositionthefiltersoverthedetectorinsequence.inadditiontotherossmethodasinglefilter(hullmethod)ornofilteratallmaybeusedtomeasuresomeelements.,nondispersivex-rayfluorescence(ndxrf),inthiscasechlorinecanbemeasuredbyusingchlorineasatransmittingfilterandsulfurasanabsorbingfilter.thedifferencebetweenthecountsofx-raysofftheoilsampleandthroughthefiltercorrelatestothechlorineconcentration.similarlyasulfurandphosphoruspairoffilterscanbeusedtomeasuresulfur.asinglefiltercanbeusedtomeasurephosphorussincethereareusuallynomeasurableelementsbelowphosphorusthatwouldproducecounts.thematterisconfusedsomewhatbecauseitisdifficulttoproducegoodsulfurandphosphorusfilters,sousuallyanelementwithanlabsorptionedgeattheappropriateenergyisusedinstead,moornbfors,andzrforp.sincetheheavymetalsaredenserthefiltersareusuallymuchthinnerthantheirkabsorptionedgecounterparts.,nondispersivex-rayfluorescence(ndxrf),exampleapplication:-oneofthemostcommonapplicationsismeasuringphosphorus,sulfurandchlorineinoil.generallyeitherafe-55radioisotope,oranx-raytubewitheitherapd,ag,ortitargetisusedtoexcitethoseelements.x-raysdonotreadilyexcitehydrogenandcarboninthebasematrixandthedetectorwindowsreadilyabsorbtheirx-rays,andsotheyarentmeasured.,totalreflectionx-rayfluorescence(txrf),totalreflectionx-rayfluorescence(txrf)andthefundamentallyrelatedgrazingemissionx-rayfluorescence(gexrf)relyonscatterpropertiesnearandbelowthebraggangletoreducebackgroundintensitiesandimprovedetectionslimitsanorderofmagnitudeormoreovermoretraditionalxrfinstruments.iflightisdirectedatasmoothsurfaceataverysmallangle(typicallylessthan0.5degreeforx-rays)virtually100%ofthelightwillbereflectedatanequallysmallangle.thisisthesameprinciplerel