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1、TheoryofTransmissionGaugingfor ThicknessMeasurement ofMetalsBasicPrincipleDetectorSourceSteel-Thickness,tBasicPrinciplesTrans-missionDetectorSourceMetal-Thickness,tBackscatterDetectorPropertiesofRadiationAllradiationhastwodistinctpropertiesEnergySimilartotheCOLORofvisiblelight,usua
2、llyexpressedinkeVormeVIntensitySimilartoBRIGHTNESSofvisiblelightLightSoundX-rays/gammaID=I0e-t/qBeer’sLaw:q=f(Material,LightColor)q=f(Material,SoundPitch)q=f(Material,keV)Brightness,IntensityColor,FrequencyVolumePitch,FrequencyNumberofPhotonsEnergy,keVThreeWaystouse RadiationforMea
3、surementThreemodesofmeasurementmaybeusedaccordingtotheapplicationTransmissionmode,usedfordirectmeasurementofstripthicknessFluorescencemode,usedtomeasurethicknessofmetalliccoatingsBackscattermode,usedtomeasurethicknessofpaintcoatingsMeasurementofThicknessMetalBlocksGamma/X-raysDetec
4、torSourceSteel-Thickness,tI0=FullIntensityI=IntensityI=I0e-t/qt=-qln(I/Io)MeasurementofThicknessMeanfreepath,q=f(keV,chemistry)DetectedBeamIntensityDetectorIntensityIDThickness0q2q6qq=thicknessatwhichI=0.37*I02q=thicknessforbestpercentnoisetosignalratio6q=maximummeasurablethickness
5、GenerationofX-rays&Gamma-raysNaturalDecayofIsotope:Am241&Cs137aremostcommonlyusedSingleFixedEnergy(Mono-chromatic)ReliableLowerCostLowPowerCannotbeturnedoffX-rayTube:HighvoltageaccelerateselectronstoatargetEnergySpectrumSelectableEnergySafer-TurnoffHVtostopradiationoutputGreaterpho
6、tonintensityLowerNoiseHigherCostRadiationSourcesforMeasuringSteelThicknessRanges-SteelSr90(Betaray)0.05-1.00mmAm241(GammaRay)0.15-6.25mmCs137(GammaRay)6.0-125mm100kV(X-ray)0.1-10.0mm160kV(X-ray)0.2-25.0mm240kV(X-ray)1.0-60.0mmRadio-IsotopeSourceOutputRadiationisemittedinalldirectio
7、ns,non-preferentiallySelf-absorptionlimitsradiationavailableformeasurementRadioactivesourceoutputisnotalinearfunctionofsourceactivityHalf-LivesofRadiationSourcesIsotopeshave“HalfLives”---thetimeforactivitytodecaytohalfoftheoriginalvalueAm241433yearsCs13730yearsCm24417.8yearsSr9029.
8、6yearsKr8510.7yearsPm1372.
