high angle neutron-proton scattering高角中子质子散射

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1、Highangleneutron-protonscattering1.ExperimentalDataOnlynucleonswithhighkineticenergyhaveenoughresolutivepowertobeusefulasprobesinthestudyofthenucleonicpotential.Therefore,thefirstneutron-protonscatteringexperimentswererunwithincidentneutronenergyof90MeV.Whenthedeepn

2、essofthenucleonicpotentialisquitesmallerthantheincidentneutronkineticenergythemaximummomentumthatthispotentialcantransfertotheneutronisquitesmallerthanitsinitialmomentumandthereforeahighchangeofthedirectionoftheneutronmomentumcannotoccur.Howeverneutron-protonscatter

3、ingunexpectedlyshowedabout50%oflowandhighanglescattering(1-7).Fig.1:Meantotalscatteringcross-sectionsofneutronsbyprotonsversusimpingingneutronenergy.Fig.2:Differentialcross-sectionMs/Mqofneutron-protonscattering.Theobservedn-pscatteringisnearlysymmetricalwithrespec

4、ttoascatteringangleof90o,evidencingthusanalmostequalpreferenceforhighanglescatteringthanforsmallones.(a)(b)Fig.3(aandb):n-pscatteringrepresentedinthecenterofmassframe:(a)Whenkineticenergiesarehighwithrespecttothedeepnessofthenucleonicpotentialthetransferofmomentumis

5、smallandthescatteringanglesoftheneutronandtheprotonaresmalltoo.(b)Althoughthemomentumtransferisequallynecessarilysmallthereisanapparenthighanglescatteringwhichproceedsfromthetransformationoftheneutronintoaprotonandviceversa.Fig.4:Animationofn-pscatteringClickheretos

6、eetheanimation:n-pscattering2.PhenomenologicaldescriptionInFig.2then-pscatteringisviewedfromareferentialframeinwhichthecenterofmassisatrest:(a)ifthekineticenergyoftheimpingingnucleonsishighwithrespecttothenucleonicpotentialwell,themomentumtransferissmall(i.e.thecoll

7、isionisalmostelastic)andthescatteringanglesaresmalltoo.(b)similarscatteringconditionsinwhichthemomentumtransferkeepsbeingsmallbutinwhichthescatteringanglesarehighduetothetransmutationofthe(impinging)protonintoa(scattered)neutronandthe(impinging)neutroninto(scattered

8、)proton.Fig.5.a:Apparenthighanglen-pscatteringFig.5.b:Effectivehighanglen-pscatteringThehighanglen-pscatteringisinterpretedhasafalsehighan