核效应分析正电子湮没技术

《核效应分析正电子湮没技术》由会员上传分享，免费在线阅读，更多相关内容在教育资源-天天文库。

1、正电子湮没技术及其应用PredictionofpositronExistenceofpositronspredictedbyPAMDiracin1928fromrelativistictheoryofelectrons.英国物理学家P.Dirac(1902---1984)Dirac’sequationimplies:positronmass=electronmasspositroncharge=+ePredictionofantimatterDiscoveryofantimatterAnders

2、on(1932)discoveredthepositronpredictedbyDiracDiscoveryofantimatterPositivelychargedelectronsdetectedincosmicrayspassingthroughacloudchamberimmersedinamagneticfieldAcloudchamber(Wilsonchamber)wasnormallyusedatthattimetodetecttracksofchargedparticles.It

3、containedasupersaturatedvapour.Whenachargedparticleentersthechamber,itcollideswithairoralcoholvapouratoms,producingfreeions(ionisationprocess).Vapourinthechambercondensesaroundthesefreeions,formingdroplets.Thedropletsarewhatformthetrail.Expansiontypec

4、loudchamberOriginalWilsonchambercloudchamberTracksofparticlesinthecloudchamberParticletrackcanbephotographed.Cloudchambercanbeplacedinamagneticfield,thusallowingthemeasurementoftheparticlemomentumwhichisinverselyproportionaltothecurvature(曲率)ofthetrac

5、kinthemagneticfield.Particlemomentumcomponentperpendiculartothefieldisp(MeV/c)=0.310-3B(gauss)r(cm)whereristheradiusofcurvature.Differenttypesofparticleswillleavedifferenttrails.Alphaparticles,whicharerelativelyheavy,willproducestraightdensetrails(le

6、ft).Slowelectronsleavewispy,irregulartrails(centre).Tracksofcosmic-rayparticlesareshownontheright.正电子的基本物理特性正电子是电子的反粒子。又称阳电子，，一般用符号e+表示。两者除电荷符号相反外,其他性质（静止质量、电荷的电量、自旋）都相同。正电子的来源（Sourceofpositron）放射性核素的正β+衰变energypositronbdecayEg=1277keV22Na宇宙射线中的正电子电子对

7、效应(Paire+-e-Production)ApassingphotoncanbeperturbedbytheEM-fieldofanatom,causingthephotontodecayintoandelectron(e-)andapositron(e+).Electromagneticenergyisconvertedintomatter(massenergy).Thisiscalledpaircreation.Chargeconserved:0e-+e+Energyconserved:

8、Minimumphotonenergy(hνmin)iswhenMomentumconserved:Nucleusrequiredtoconservelinearmomentum.(agammaray)能量≥1.02MeV的γ射线与原子核作用可能产生一对正-负电子。能量转化成质量M=E/C2M＋γ→M+e++e-1.02MeVmeme基本条件：Eγ1.02MeV电子对效应(续上)正-负电子云雾室径迹图正电子湮没(PositronAnnihilation)正电子进入物质在短时间内迅