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1、Chapter12NuclearPhysics(June10,2005)Errorcorrections:Chapter11,question6,findthe“intensity”,not“density”SummarytothelastlectureThefundamentalprinciplesoflaserAtomicenergylevels:ground,metastableandexcitedstatesAbsorption;spontaneousemission,stimulatedemission.Atomicdistributionandpopulation
2、inversionOpticalResonator2.ThecharacteristicsoflaserGooddirectionalityHighbrightnessandhighintensity.GoodmonochromaticGoodcoherence(time&spatial相干性)Goodpolarization(偏振)12.1ThebasicpropertiesofnucleusInproceedingchapterswehavefrequentlymadeuseofthefactthateveryatomcontainsamassive,positively
3、chargednucleus,muchsmallerthantheoveralldimensionsoftheatombutneverthelesscontainingmostofthetotalmassoftheatom.Itisinstructivetoreviewtheearliestexperimentalevidencefortheexistenceofthenucleus.Itiswellknownthatanatomhasanucleusinthecenteroftheatom.Themostobviousfeatureoftheatomicnucleusisi
4、tssize,oftheorderof20,000to200,000timessmallerthantheatomitself.Althoughthe“surface”ofanucleusisnotasharpboundary,experimentsdeterminedanapproximateradiusforeachnucleus.Theradiusisfoundtodependonthemass,whichinturndependsonthetotalnumberAofneutronsandprotons,usuallycalledmassnumber.12.1.1th
5、estructuresofnucleus(核子)Theelectricalchargesofnucleus:Nucleusiscomposedofprotonsandneutrons.Proton（positivecharge）andneutrons（noelectroniccharges）.Nucleushaspositivechargesanditrotates.Becauseofthis,ithasangularmomentumandmagneticmoment.Thetotalnumberofpositivecharges,thenumberofprotons,isd
6、enotedbyZwhichisalsocelledtheatomicnumber.Nuclearmasses:Massofanatomincludesthemassofelectronsandthemassofnucleus.Asthemassofaprotonoraneutronisverycloseto1u,theatomicmassnumberAisequaltothetotalnumberofprotonsandneutrons.Therefore,AtomicmassnumberAtomicnumberSymbolofatomsA=Z+NNumberofneutr
7、onsAtomicmassunit(u)12.1.2Nuclearproperties1.Thesizeanddensityofthenucleus:Theradiiofmostnucleiarerepresentedfairlywellbytheempiricalequation1fm=10-15mr0isanempiricalconstant1.2×10-15m,thesamesizeforallnuclei.Thedensityofnucleoncouldbefoundasfollows:Wher
