大学物理实验报告英文版--X光Word格式文档下载.doc

大学物理实验报告英文版--X光Word格式文档下载.doc

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Amoresophisticatedx-raydetectoristheso-calledGeiger-Mullercounter,aninstrumentfordetectingthepresenceofandmeasuringionizingradiationsuchasthex-rays.Itconvertstheintensityofthex-rayintocountingrates.Wewillusesuchadeviceinourlab.

Attenuationofx-rays:

Whenpassingthroughamaterial,x-raycanbeattenuatedbyE&

Minteractions.Foraslabofthicknessx,thetransmission（definedastheratioofthetransmittedradiationtotheincoming）,.µ

istheattenuationcoefficient,withadimensionof1/distance.µ

isacharacterofthematerial,anditvaries,forexample,asafunctionofatomicnumber.Wewillstudythisdependenceinthislab.

BraggDiffraction

Likenormallights,whenx-raytransmitthroughmaterialwithregularopticalpattern（e.g.lattice）,diffractionwillhappenifthewavelengthofthex-rayisclosetothelatticespace.Suchdiffractiononthecrystalistheso-calledBraggDiffraction.Ifthelatticespacingisd,andthex-rayandthecrystalsurfaceformsanangleq,theanglewheremaximumdiffractionhappenswillsatisfy

wherenisanintegerandlisthewavelength.

Labequipment:

Theequipmentisanx-raylabsystemmadebyLeyboldInc.Aschematicisshownbelow.

Thex-rayisgeneratedbyanelectronbeamwithcontrollableenergy（viathepotential）andcurrent.Thex-rayisgoingintothedetectionchambertotheright.Thereisaremovableaperturewhichfocusesthex-ray,arotatablesampleholder,andarotatableG-Mcounter.Attherightendofthewall,thereisafluorescencescreenforimagine.

Operationdetailsofthedevicewillbegivenbythemanual.Basically,youneedtosetthehighvoltage（U）whichdeterminetheenergyofthex-ray,thecurrent（I）,andtheangleofthesampleholder（target）orthedetector.Aknobcanbeusedtomaketheadjustmentonselectedparameters.“Coupled”movementmeansonemovesthetargetandthedetectortogether,theformerbyananglea,andthelatterbyanangle2a.Makesuretheleadglasswindowisclosedbeforeyouturnonthehighvoltage.

Attenuator（target）

Left:

aluminumattenuatormountedonacurvedplatewiththicknessof0，0.5,1.0,1.5,2.0,2.5,and3mm.Onecanselectdifferentthicknessbyselectingangle.

Right:

attenuationofdifferentmaterials,allwithathicknessof0.5mm,includingPolystyrene（averageZ=6）,Aluminum（13）,Iron（26）,Copper（29）,Zirconium（40）andSilver（47）.

2.Installtheaperture.InstalltheZrfoilontotheaperture.ThisistofilterouttheKαline.SqueezetheNaClcrystalontothesampleholder.InthispartoftheprocedureweneedtomakesurethattheXraybeam,thecrystalsurfaceandthedetectorisaligned.UsethefollowingalignmentprocedurebytheBraggDiffraction,theprocessisomitted.

data:

Thefirstpeakappearswhenit’s7.5degree.

1.analysis:

Then,m.

Thatis,thewavelengthofXrayism.

2.MeasuretheXrayattenuationtodifferentthickness:

InstalltheZrfoilontotheaperture.SetHV=21kV,I=0.05mA,Db=0,Dt=100s.Hittargetkey.Changetheanglesequentiallyto0,10,20,30,40,50,60degree（thethicknessoftheattenuationincreaseby0.5mmeachstep）.Foreachofthissetting,hit“scan”totakethedata,andhit“replay”togettheaveragerate.

attenuationofdifferentthickness

thickness（mm）

0.5

1

1.5

2

2.5

3

Data（1/s）

21.4

9.6

4.4

2.8

1.7

Fittherateasafunctionofthickness（withbackgroundsubtraction）togettheattenuationcoefficient.Fitthedatainoriginwithexponentialfit（mode=expdec1）,throughequation.Weformthegraphof1/Tandx.So,wegetthat

Hence,So,theattenuationcoefficientis.

MeasuretheXrayattenuationtomaterialswithdifferentatomicmass:

a）RemovetheZrfilter.InsertthecurvedattenuatorholderB（differenttarget）intotheannulusslotontheplasticmount.SetHV=30kV,I=1mA,Db=0,Dt=100s.Hittargetkey.Changetheanglesequentiallyto0,10,20,30,40,50,60degree,eachcorrespondingtoagivenmaterial.

b）Foreachofthissetting,hit“scan”totakethedata,andhit“replay”togettheaveragerate.

c）ForthescanwithZrfilter.

attenuationofdifferentZ,withZr

Z

6

13

26

29

40

47

9117.9

7627.4

72.9

7.7

108.9

14.4

Noexactrulecanbefound.

InstalltheZrfilter.RepeatofZnumber.Thegraphturnsout:

attenuationofdifferentZ,withoutZr

9025.4

9027.8

8308.4

75.2

5.2

74.8

PlottherateasafunctionofZnumber.

Also,noexactrulecanbefound.

Conclusion:

1.thewavelengthofXrayism.

2.TheratehasnoexactrelationshipwithZ.

Error:

WhetherIcheckthebackgroundornotwillhaveainfluenceonthewavelength.

ThelightintheroomwillmaybeinfluencethedataIgot.WhenIdidtheexperimentwiththelighton,thusthelightwillbestronger.