Non-Destructive-Testing-03教学讲解课件

Non-destructiveTesting

ZhangLihui

IWE&CWINon-destructiveTesting

ZhanReference:“IntroductiontoNondestructiveTesting-ATrainingGuide”,P.E.Mix,JohnWiley&Sons.“NDEHandbook-Non-destructiveexaminationmethodsforconditionmonitoring”,ed.K.G.Bøving,ButterworthsReference:Theuseofnoninvasivetechniquestodeterminetheintegrityofamaterial,componentorstructure orquantitativelymeasuresomecharacteristicofanobject.

i.e.Inspectormeasurewithoutdoingharm.DefinitionofNDT(NDE)Theuseofnoninvasivei.e.IWhatareSomeUses

ofNDEMethods?FlawDetectionandEvaluationLeakDetectionLocationDeterminationDimensionalMeasurementsStructureandMicrostructureCharacterizationEstimationofMechanicalandPhysicalPropertiesStress(Strain)andDynamicResponseMeasurementsMaterialSortingandChemicalCompositionDeterminationFluorescentpenetrantindicationWhatareSomeUses

ofNDEMetWhyNondestructive?TestpiecetooprecioustobedestroyedTestpiecetobereuseafterinspectionTestpieceisinserviceForqualitycontrolpurposeSomethingyousimplycannotdoharmto,e.g.fetusinmother’suterusWhyNondestructive?TestpieceWhenareNDEMethodsUsed?ToassistinproductdevelopmentToscreenorsortincomingmaterialsTomonitor,improveorcontrolmanufacturingprocessesToverifyproperprocessingsuchasheattreatingToverifyproperassemblyToinspectforin-servicedamageThereareNDEapplicationatalmostanystageintheproductionorlifecycleofacomponent.WhenareNDEMethodsUsed?ToaMajortypesofNDTDetectionofsurfaceflawsVisualMagneticParticleInspectionFluorescentDyePenetrantInspectionDetectionofinternalflawsRadiographyUltrasonicTestingEddycurrentTestingMajortypesofNDTDetectionofMostbasicandcommoninspectionmethod.Toolsincludefiberscopes,borescopes,magnifyingglassesandmirrors.Roboticcrawlerspermitobservationinhazardousortightareas,suchasairducts,reactors,pipelines.Portablevideoinspectionunitwithzoomallowsinspectionoflargetanksandvessels,railroadtankcars,sewerlines.1.VisualInspectionMostbasicandcommoninspecti2.MagneticParticleInspection(MPI)2.1IntroductionAnondestructivetestingmethodusedfordefectdetection.FastandrelativelyeasytoapplyandpartsurfacepreparationisnotascriticalasforsomeotherNDTmethods.–MPIoneofthemostwidelyutilizednondestructivetestingmethods.MPIusesmagneticfieldsandsmallmagneticparticles,suchasironfilingstodetectflawsincomponents.Theonlyrequirementfromaninspectabilitystandpointisthatthecomponentbeinginspectedmustbemadeofaferromagneticmaterialsuchasiron,nickel,cobalt,orsomeoftheiralloys.Ferromagneticmaterialsarematerialsthatcanbemagnetizedtoalevelthatwillallowtheinspectiontobeaffective.Themethodisusedtoinspectavarietyofproductformssuchascastings,forgings,andweldments.Manydifferentindustriesusemagneticparticleinspectionfordeterminingacomponent'sfitness-for-use.Someexamplesofindustriesthatusemagneticparticleinspectionarethestructuralsteel,automotive,petrochemical,powergeneration,andaerospaceindustries.Underwaterinspectionisanotherareawheremagneticparticleinspectionmaybeusedtotestsuchthingsasoffshorestructuresandunderwaterpipelines.2.MagneticParticleInspectio2.2BasicPrinciplesIntheory,magneticparticleinspection(MPI)isarelativelysimpleconcept.Itcanbeconsideredasacombinationoftwonondestructivetestingmethods:magneticfluxleakagetestingandvisualtesting.Considerabarmagnet.Ithasamagneticfieldinandaroundthemagnet.Anyplacethatamagneticlineofforceexitsorentersthemagnetiscalledapole.Apolewhereamagneticlineofforceexitsthemagnetiscalledanorthpoleandapolewherealineofforceentersthemagnetiscalledasouthpole.2.2BasicPrinciplesInteractionofmaterialswithanexternalmagneticfieldWhenamaterialisplacedwithinamagneticfield,themagneticforcesofthematerial'selectronswillbeaffected.ThiseffectisknownasFaraday'sLawofMagneticInduction.

However,materialscanreactquitedifferentlytothepresenceofanexternalmagneticfield.Thisreactionisdependentonanumberoffactorssuchastheatomicandmolecularstructureofthematerial,andthenetmagneticfieldassociatedwiththeatoms.Themagneticmomentsassociatedwithatomshavethreeorigins.Thesearetheelectronorbitalmotion,thechangeinorbitalmotioncausedbyanexternalmagneticfield,andthespinoftheelectrons.InteractionofmaterialswithDiamagnetic,Paramagnetic,andFerromagneticMaterialsDiamagneticmetals:veryweakandnegativesusceptibilitytomagneticfields.Diamagneticmaterialsareslightlyrepelledbyamagneticfieldandthematerialdoesnotretainthemagneticpropertieswhentheexternalfieldisremoved.Paramagneticmetals:smallandpositivesusceptibilitytomagneticfields.Thesematerialsareslightlyattractedbyamagneticfieldandthematerialdoesnotretainthemagneticpropertieswhentheexternalfieldisremoved.Ferromagneticmaterials:largeandpositivesusceptibilitytoanexternalmagneticfield.Theyexhibitastrongattractiontomagneticfieldsandareabletoretaintheirmagneticpropertiesaftertheexternalfieldhasbeenremoved.Diamagnetic,Paramagnetic,andFerromagneticmaterialsbecomemagnetizedwhenthemagneticdomainswithinthematerialarealigned.Thiscanbedonebyplacingthematerialinastrongexternalmagneticfieldorbypasseselectricalcurrentthroughthematerial.Someorallofthedomainscanbecomealigned.Themoredomainsthatarealigned,thestrongerthemagneticfieldinthematerial.Whenallofthedomainsarealigned,thematerialissaidtobemagneticallysaturated.Whenamaterialismagneticallysaturated,noadditionalamountofexternalmagnetizationforcewillcauseanincreaseinitsinternallevelofmagnetization.

UnmagnetizedmaterialMagnetizedmaterialFerromagneticmaterialsbecome

GeneralPropertiesofMagneticLinesofForceFollowthepathofleastresistancebetweenoppositemagneticpoles.Nevercrossoneanother.Allhavethesamestrength.Theirdensitydecreases(theyspreadout)whentheymovefromanareaofhigherpermeabilitytoanareaoflowerpermeability.Theirdensitydecreaseswithincreasingdistancefromthepoles.flowfromthesouthpoletothenorthpolewithinthematerialandnorthpoletosouthpoleinair.

Whenabarmagnetisbrokeninthecenterofitslength,twocompletebarmagnetswithmagneticpolesoneachendofeachpiecewillresult.Ifthemagnetisjustcrackedbutnotbrokencompletelyintwo,anorthandsouthpolewillformateachedgeofthecrack.

Themagneticfieldexitsthenorthpoleandreenterstheatthesouthpole.Themagneticfieldspreadsoutwhenitencounterthesmallairgapcreatedbythecrackbecausetheaircannotsupportasmuchmagneticfieldperunitvolumeasthemagnetcan.Whenthefieldspreadsout,itappearstoleakoutofthematerialand,thus,itiscalledafluxleakagefield.

WhenabarmagnetisbrokeninIfironparticlesaresprinkledonacrackedmagnet,theparticleswillbeattractedtoandclusternotonlyatthepolesattheendsofthemagnetbutalsoatthepolesattheedgesofthecrack.Thisclusterofparticlesismucheasiertoseethantheactualcrackandthisisthebasisformagneticparticleinspection.

IfironparticlesaresprinkleMagneticParticleInspectionThemagneticfluxlineclosetothesurfaceofaferromagneticmaterialtendstofollowthesurfaceprofileofthematerialDiscontinuities(cracksorvoids)ofthematerialperpendiculartothefluxlinescausefringingofthemagneticfluxlines,i.e.fluxleakageTheleakagefieldcanattractotherferromagneticparticlesMagneticParticleInspectionThCracksjustbelowthesurfacecanalsoberevealedThemagneticparticlesformaridgemanytimeswiderthanthecrackitself,thusmakingtheotherwiseinvisiblecrackvisibleCracksjustbelowthesurfaceTheeffectivenessofMPIdependsstronglyontheorientationofthecrackrelatedtothefluxlinesMPIisnotsensitivetoshallowandsmoothsurfacedefectsTheeffectivenessofMPIdepen2.3TestingProcedureofMPICleaningDemagnetizationContrastdyes(e.g.whitepaintfordarkparticles)MagnetizingtheobjectAdditionofmagneticparticlesIlluminationduringinspection(e.g.UVlamp)InterpretationDemagnetization-preventaccumulationofironparticlesorinfluencetosensitiveinstruments2.3TestingProcedureofMPIClMagnetizingtheobjectThereareavarietyofmethodsthatcanbeusedtoestablishamagneticfieldinacomponentforevaluationusingmagneticparticleinspection.Itiscommontoclassifythemagnetizingmethodsaseitherdirectorindirect.

Directmagnetization:currentispasseddirectlythroughthecomponent.ClampingthecomponentbetweentwoelectricalcontactsinaspecialpieceofequipmentUsingclamsorprods,whichareattachedorplacedincontactwiththecomponentMagnetizingtheobjectTherearIndirectmagnetization:usingastrongexternalmagneticfieldtoestablishamagneticfieldwithinthecomponent

(a)permanentmagnets

(b)Electromagnets(c)coilshotIndirectmagnetization:usingLongitudinalmagnetization:achievedbymeansofpermanentmagnetorelectromagnetCircumferentialmagnetization:achievedbysendinganelectriccurrentthroughtheobjectLongitudinalmagnetization:aasolidconductorofamagneticmaterialcarryingalternatingcurrent.anonmagneticmaterialcarryingdirectcurrent.asolidconductorofamagneticmaterialcarryingdirectcurrent.CircumferentialmagneticfielddistributionEitherAC,DCorpulsedDCcanbeusedasolidconductorofamagnetiDemagnetizationAfterconductingamagneticparticleinspection,itisusuallynecessarytodemagnetizethecomponent.Remanentmagneticfieldscan:erferewithelectronicequipmentsuchasacompass.cancreateaconditionknownas"arkblow"intheweldingprocess.Arcblowmaycausestheweldarctowonderorfillermetaltoberepelledfromtheweld.causeabrasiveparticletoclingtobearingorfayingsurfacesandincreasewear.DemagnetizationMagneticparticlesPulverizedironoxide(Fe3O4)orcarbonylironpowdercanbeusedColouredorevenfluorescentmagneticpowdercanbeusedtoincreasevisibilityPowdercaneitherbeuseddryorsuspendedinliquid

MagneticparticlesPulverizediSomeStandardsforMPIProcedureBritishStandardsBSM.35:AerospaceSeries:MagneticParticleFlawDetectionofMaterialsandComponentsBS4397:MethodsformagneticparticletestingofweldsASTMStandardsASTME709-80:StandardPracticeforMagneticParticleExaminationASTME125-63:Standardreferencephotographsformagneticparticleindicationsonferrouscastingsetc….SomeStandardsforMPIProceduOneofthemostdependableandsensitivemethodsforsurfacedefectsfast,simpleandinexpensivedirect,visibleindicationonsurfaceunaffectedbypossibledeposits,e.g.oil,greaseorothermetalschips,inthecrackscanbeusedonpaintedobjectssurfacepreparationnotrequiredresultsreadilydocumentedwithphotoortapeimpression2.4AdvantagesofMPIOneofthemostdependableand2.5LimitationsofMPIOnlygoodforferromagneticmaterialssub-surfacedefectswillnotalwaysbeindicatedrelativedirectionbetweenthemagneticfieldandthedefectlineisimportantobjectsmustbedemagnetizedbeforeandaftertheexaminationthecurrentmagnetizationmaycauseburnscarsontheitemexamined2.5LimitationsofMPIOnlygooExamplesofvisibledrymagneticparticleindications

IndicationofacrackinasawbladeIndicationofcracksinaweldment

BeforeandafterinspectionpicturesofcracksemanatingfromaholeIndicationofcracksrunningbetweenattachmentholesinahingeExamplesofvisibledrymagnetExamplesofFluorescentWetMagneticParticleIndicationsMagneticparticlewetfluorescentindicationofacracksinadriveshaftMagneticparticlewetfluorescentindicationofacrackinabearing

MagneticparticlewetfluorescentindicationofacracksatafastenerholeExamplesofFluorescentWetMaNon-Destructive-Testing_03教学讲解课件3.DyePenetrantInspectionLiquidpenetrantinspection(LPI)isoneofthemostwidelyusednondestructiveevaluation(NDE)methods.Itspopularitycanbeattributedtotwomainfactors,whichareitsrelativeeaseofuseanditsflexibility.LPIcanbeusedtoinspectalmostanymaterialprovidedthatitssurfaceisnotextremelyroughorporous.MaterialsthatarecommonlyinspectedusingLPIincludemetals(aluminum,copper,steel,titanium,etc.),glass,manyceramicmaterials,rubber,andplastics.3.DyePenetrantInspectionLiqLiquidpenetrationinspectionisamethodthatisusedtorevealsurfacebreakingflawsbybleedoutofacoloredorfluorescentdyefromtheflaw.Thetechniqueisbasedontheabilityofaliquidtobedrawnintoa"clean"surfacebreakingflawbycapillaryaction.Afteraperiodoftimecalledthe"dwell,"excesssurfacepenetrantisremovedandadeveloperapplied.Thisactsasa"blotter."Itdrawsthepenetrantfromtheflawtorevealitspresence.Colored(contrast)penetrantsrequiregoodwhitelightwhilefluorescentpenetrantsneedtobeusedindarkenedconditionswithanultraviolet"blacklight".UnlikeMPI,thismethodcanbeusedinnon-ferromagneticmaterialsandevennon-metalsModernmethodscanrevealcracks2mwideStandard:ASTME165-80LiquidPenetrantInspectionMethod3.1IntroductionLiquidpenetrationinspectionWhyLiquidPenetrantInspection?ToimprovesthedetectabilityofflawsTherearebasicallytwowaysthatapenetrantinspectionprocessmakesflawsmoreeasilyseen.LPIproducesaflawindicationthatismuchlargerandeasierfortheeyetodetectthantheflawitself.LPIproducesaflawindicationwithahighlevelofcontrastbetweentheindicationandthebackground.Theadvantagethataliquidpenetrantinspection(LPI)offersoveranunaidedvisualinspectionisthatitmakesdefectseasiertoseefortheinspector.WhyLiquidPenetrantInspectioSurfacePreparation:

Oneofthemostcriticalstepsofaliquidpenetrantinspectionisthesurfacepreparation.Thesurfacemustbefreeofoil,grease,water,orothercontaminantsthatmaypreventpenetrantfromenteringflaws.Thesamplemayalsorequireetchingifmechanicaloperationssuchasmachining,sanding,orgritblastinghavebeenperformed.Theseandothermechanicaloperationscansmearthesurfaceofthesample,thusclosingthedefects.

PenetrantApplication:Oncethesurfacehasbeenthoroughlycleanedanddried,thepenetrantmaterialisappliedbyspraying,brushing,orimmersingthepartsinapenetrantbath.

PenetrantDwell:

Thepenetrantisleftonthesurfaceforasufficienttimetoallowasmuchpenetrantaspossibletobedrawnfromortoseepintoadefect.Thetimesvarydependingontheapplication,penetrantmaterialsused,thematerial,theformofthematerialbeinginspected,andthetypeofdefectbeinginspected.Generally,thereisnoharminusingalongerpenetrantdwelltimeaslongasthepenetrantisnotallowedtodry.

3.2BasicprocessingstepsofLPISurfacePreparation:OneofthExcessPenetrantRemoval:Thisisthemostdelicatepartoftheinspectionprocedurebecausetheexcesspenetrantmustberemovedfromthesurfaceofthesamplewhileremovingaslittlepenetrantaspossiblefromdefects.Dependingonthepenetrantsystemused,thisstepmayinvolvecleaningwithasolvent,directrinsingwithwater,orfirsttreatedwithanemulsifierandthenrinsingwithwater.

DeveloperApplication:

Athinlayerofdeveloperisthenappliedtothesampletodrawpenetranttrappedinflawsbacktothesurfacewhereitwillbevisible.Developerscomeinavarietyofformsthatmaybeappliedbydusting(drypowdered),dipping,orspraying(wetdevelopers).

IndicationDevelopment:Thedeveloperisallowedtostandonthepartsurfaceforaperiodoftimesufficienttopermittheextractionofthetrappedpenetrantoutofanysurfaceflaws.Thisdevelopmenttimeisusuallyaminimumof10minutesandsignificantlylongertimesmaybenecessaryfortightcracks.

ExcessPenetrantRemoval:ThisInspection:Inspectionisthenperformedunderappropriatelightingtodetectindicationsfromanyflawswhichmaybepresent.

CleanSurface:Thefinalstepintheprocessistothoroughlycleanthepartsurfacetoremovethedeveloperfromthepartsthatwerefoundtobeacceptable.Inspection:InspectionisthenPenetranttestingmaterialsApenetrantmustpossessanumberofimportantcharacteristics.Apenetrantmustspreadeasilyoverthesurfaceofthematerialbeinginspectedtoprovidecompleteandevencoverage.bedrawnintosurfacebreakingdefectsbycapillaryaction.remaininthedefectbutremoveeasilyfromthesurfaceofthepart.remainfluidsoitcanbedrawnbacktothesurfaceofthepartthroughthedryinganddevelopingsteps.behighlyvisibleorfluorescebrightlytoproduceeasytoseeindications.mustnotbeharmfultothematerialbeingtestedortheinspector.PenetranttestingmaterialsApPenetrantTypesDyepenetrantsTheliquidsarecolouredsothattheyprovidegoodcontrastagainstthedeveloperUsuallyredliquidagainstwhitedeveloperObservationperformedinordinarydaylightorgoodindoorilluminationFluorescentpenetrantsLiquidcontainadditivestogivefluorescenceunderUVObjectshouldbeshieldedfromvisiblelightduringinspectionFluorescentindicationsareeasytoseeinthedarkStandard:AerospaceMaterialSpecification(AMS)2644.PenetrantTypesDyepenetrantsFBasedonthestrengthordetectabilityoftheindicationthatisproducedforanumberofverysmallandtightfatiguecracks,penetrantscanbeclassifiedintofivesensitivitylevelsareshownbelow:Level½-UltraLowSensitivityLevel1-LowSensitivityLevel2-MediumSensitivityLevel3-HighSensitivityLevel4-Ultra-HighSensitivityAccordingtothemethodusedtoremovetheexcesspenetrantfromthepart,thepenetrantscanbeclassifiedinto:

MethodA-WaterWashableMethodB-PostEmulsifiable,LipophilicMethodC-SolventRemovableMethodD-PostEmulsifiable,HydrophilicFurtherclassificationBasedonthestrengthordetecEmulsifiersWhenremovalofthepenetrantfromthedefectduetoover-washingofthepartisaconcern,apostemulsifiablepenetrantsystemcanbeused.Postemulsifiablepenetrantsrequireaseparateemulsifiertobreakthepenetrantdownandmakeitwaterwashable.Lipophilicemulsificationsystemsareoil-basedmaterialsthataresuppliedinready-to-useform.Hydrophilicsystemsarewater-basedandsuppliedasaconcentratethatmustbedilutedwithwaterpriortouse.MethodB-LipophilicEmulsifier,MethodD-HydrophilicEmulsifierEmulsifiersWhenremovaloftheDeveloperTheroleofthedeveloperistopullthetrappedpenetrantmaterialoutofdefectsandtospreadthedeveloperoutonthesurfaceofthepartsoitcanbeseenbyaninspector.Thefinedeveloperparticlesbothreflectandrefracttheincidentultravioletlight,allowingmoreofittointeractwiththepenetrant,causingmoreefficientfluorescence.Thedeveloperalsoallowsmorelighttobeemittedthroughthesamemechanism.ThisiswhyindicationsarebrighterthanthepenetrantitselfunderUVlight.Anotherfunctionthatsomedevelopersperformsistocreateawhitebackgroundsothereisagreaterdegreeofcontrastbetweentheindicationandthesurroundingbackground.DeveloperTheroleofthedevelDrypowderdeveloper–theleastsensitivebutinexpensiveWatersoluble–consistofagroupofchemicalsthataredissolvedinwaterandformadeveloperlayerwhenthewaterisevaporatedaway.Watersuspendible–consistofinsolubledeveloperparticlessuspendedinwater.Nonaqueous–suspendthedeveloperinavolatilesolventandaretypicallyappliedwithaspraygun.DeveloperTypesUsingdyeanddeveloperfromdifferentmanufacturersshouldbeavoided.Drypowderdeveloper–theleas3.3FindingLeakswithDyePenetrant3.3FindingLeakswithDyePen3.4PrimaryAdvantages

Themethodhashighsensitivetosmallsurfacediscontinuities.Themethodhasfewmateriallimitations,i.e.metallicandnonmetallic,magneticandnonmagnetic,andconductiveandnonconductivematerialsmaybeinspected.Largeareasandlargevolumesofparts/materialscanbeinspectedrapidlyandatlowcost.Partswithcomplexgeometricshapesareroutinelyinspected.Indicationsareproduceddirectlyonthesurfaceofthepartandconstituteavisualrepresentationoftheflaw.Aerosolspraycansmakepenetrantmaterialsveryportable.Penetrantmaterialsandassociatedequipmentarerelativelyinexpensive.3.4PrimaryAdvantages3.5PrimaryDisadvantagesOnlysurfacebreakingdefectscanbedetected.Onlymaterialswitharelativenonporoussurfacecanbeinspected.Precleaningiscriticalascontaminantscanmaskdefects.Metalsmearingfrommachining,grinding,andgritorvaporblastingmustberemovedpriortoLPI.Theinspectormusthavedirectaccesstothesurfacebeinginspected.Surfacefinishandroughnesscanaffectinspectionsensitivity.Multipleprocessoperationsmustbeperformedandcontrolled.Postcleaningofacceptablepartsormaterialsisrequired.Chemicalhandlingandproperdisposalisrequired.3.5PrimaryDisadvantages4.RadiographyRadiographyinvolvestheuseofpenetratinggamma-orX-radiationtoexaminematerial'sandproduct'sdefectsandinternalfeatures.AnX-raymachineorradioactiveisotopeisusedasasourceofradiation.Radiationisdirectedthroughapartandontofilmorothermedia.Theresultingshadowgraphshowstheinternalfeaturesandsoundnessofthepart.Materialthicknessanddensitychangesareindicatedaslighterordarkerareasonthefilm.Thedarkerareasintheradiographbelowrepresentinternalvoidsinthecomponent.HighElectricalPotentialElectrons-+X-rayGeneratororRadioactiveSourceCreatesRadiationExposureRecordingDeviceRadiationPenetratetheSample4.RadiographyRadiographyinvo4.1Radiationsources4.1.1x-raysourceX-raysorgammaradiationisusedX-raysareelectromagneticradiationwithveryshortwavelength(10-8-10-12m)Theenergyofthex-raycanbecalculatedwiththeequationE=h=hc/ e.g.thex-rayphotonwithwavelength1Åhasenergy12.5keVPropertiesandGenerationofX-ray4.1Radiationsources4.1.1x-rtargetX-raysWVacuumProductionofX-raysX-raysareproducedwheneverhigh-speedelectronscollidewithametaltarget.A

sourceofelectrons

–hotWfilament,a

highacceleratingvoltage(30-50kV)betweenthecathode(W)andtheanodeanda

metaltarget.Theanodeisawater-cooledblockofCucontainingdesiredtargetmetal.targetX-raysWVacuumProductionX-raySpectrumAspectrumofx-rayisproducedasaresultoftheinteractionbetweentheincomingelectronsandtheinnershellelectronsofthetargetelement.Twocomponentsofthespectrumcanbeidentified,namely,thecontinuousspectrumandthecharacteristicspectrum.SWL-short-wavelengthlimit

continuousradiationcharacteristicradiationkkIX-raySpectrumAspectrumofx-Fastmovinge-willthenbedeflectedordeceleratedandEMradiationwillbeemitted.Theenergyoftheradiationdependsontheseverityofthedeceleration,whichismoreorlessrandom,andthushasacontinuousdistribution.Theseradiationiscalledwhiteradiationorbremsstrahlung(Germanwordfor‘brakingradiation’).IfanincomingelectronhassufficientkineticenergyforknockingoutanelectronoftheKshell(theinner-mostshell),itmayexcitetheatomtoanhigh-energystate(Kstate).OneoftheouterelectronfallsintotheK-shellvacancy,emittingtheexcessenergyasax-rayphoton--K-shellemissionRadiation.Fastmovinge-willthenbedAllx-raysareabsorbedtosomeextentinpassingthroughmatterduetoelectronejectionorscattering.Theabsorptionfollowstheequationwhere Iisthetransmittedintensity;xisthethicknessofthematter;isthelinearabsorptioncoefficient(elementdependent);isthedensityofthematter;(/)isthemassabsorptioncoefficient(cm2/gm).Absorptionofx-rayI0I,xAllx-raysareabsorbedtosom4.1.2RadioIsotope(Gamma)SourcesEmittedgammaradiationisoneofthethreetypesofnaturalradioactivity.Itisthemostenergeticformofelectromagneticradiation,withaveryshortwavelengthoflessthanone-tenthofanano-meter.Gammaraysareessentiallyveryenergeticx-raysemittedbyexcitednuclei.Theyoftenaccompanyalphaorbetaparticles,becauseanucleusemittingthoseparticlesmaybeleftinanexcited(higher-energy)state.Manmadesourcesareproducedbyintroducinganextraneutrontoatomsofthesourcematerial.Asthematerialridsitselfoftheneutron,energyisreleasedintheformofgammarays.TwoofthemorecommonindustrialGamma-raysourcesareIridium-192andColbalt-60.Theseisotopesemitradiationintwoorthreediscreetwavelengths.Cobalt60willemita1.33anda1.17MeVgammaray,andiridium-192willemit0.31,0.47,and0.60MeVgammarays.Advantagesofgammaraysourcesincludeportabilityandtheabilitytopenetratethickmaterialsinarelativityshorttime.Disadvantagesincludeshieldingrequirementsandsafetyconsiderations.4.1.2RadioIsotope(Gamma)So4.2FilmRadiographyTopviewofdevelopedfilm

X-rayfilmThepartisplacedbetweentheradiationsourcean