資源描述：
《核效應(yīng)分析正電子湮沒(méi)技術(shù)》由會(huì)員上傳分享，免費(fèi)在線(xiàn)閱讀，更多相關(guān)內(nèi)容在教育資源-天天文庫(kù)。
1、正電子湮沒(méi)技術(shù) 及其應(yīng)用PredictionofpositronExistenceofpositronspredictedbyPAMDiracin1928fromrelativistictheoryofelectrons.英國(guó)物理學(xué)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.正電子的基本物理特性正電子是電子的反粒子。又稱(chēng)陽(yáng)電子，，一般用符號(hào)e+表示。兩者除電荷符號(hào)相反外,其他性質(zhì)（靜止質(zhì)量、電荷的電量、自旋）都相同。正電子的來(lái)源（Sourceofpositron）放射性核素的正β+衰變energypositronbdecayEg=1277keV22Na宇宙射線(xiàn)中的正電子電子對(duì)
7、效應(yīng)(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射線(xiàn)與原子核作用可能產(chǎn)生一對(duì)正-負(fù)電子。能量轉(zhuǎn)化成質(zhì)量M=E/C2M＋γ→M+e++e-1.02MeVmeme基本條件：Eγ?1.02MeV電子對(duì)效應(yīng)(續(xù)上)正-負(fù)電子云霧室徑跡圖正電子湮沒(méi)(PositronAnnihilation)正電子進(jìn)入物質(zhì)在短時(shí)間內(nèi)迅
