M42_KNIG7655_03_ITG_CH42

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1、CHAPTER42NuclearPhysicsRecommendedclassdays:2minimum,3preferredBackgroundInformationToday’sstudentsmayhavegrownupinthenuclearage,buttheyknowvirtuallynothingaboutnucleiornuclearphysics.UnpublishedpapersgivenatAAPTmeetingshavereportedthefollowingstudentdifficultieswithandbeliefsaboutradioa

2、ctivity:•Noawarenessofwhatalpha,beta,andgammadecayare.•Radioactivityissomehowduetoorbitalelectrons.•Sincehalfofasampleisgoneafteronehalflife,allwillbegoneaftertwohalflives.•Theprobabilityofnucleardecaydependsontheageofasample.•Nuclei“disappear”afterradioactivedecay.Manystudentsdon’trecog

3、nizethatadecayingnucleussimplybecomessomeothertypeofnucleus.•Objectsbecomeradioactivebyexposuretoradioactivity.•Noawarenessofthe(admittedlyconfusing)distinctionbetweenradiationandionizingradiation.Inanalgebra-basedclass,70%ofstudentsthoughtthataglowinglightbulbwouldincreasetheclickrateof

4、ageigercounter.Thesearenotsomuchmisconceptionsastheyareasimplelackofinformation.Studentsmighthavehadasmallexposuretonuclearphysicsinhigh-schoolchemistry,butformanythisistheirfirstlookatthenucleus.StudentLearningObjectives•Tounderstandthesizeandstructureofthenucleus.•Tolearnabouttheproper

5、tiesofthestrongforce.42-1•Toapplyandinterpretasimpleshellmodelofthenucleus.•Tounderstandradioactivedecayandhalflives.•Tolearnaboutradiationdoseandbiologicalapplicationsofnuclearphysics.PedagogicalApproachThischapteremphasizesnuclearstructureandradioactivedecay.Chapter40developedquantumph

6、ysicstothepointwherewecannowuseasimpleshellmodeltounderstandsomeofthebasicpropertiesofnuclei.TheemphasisonstructureanddecayparallelsthetreatmentofatomicphysicsinChapter41.Nuclearreactionsarenotcovered,althoughfissionwastoucheduponbrieflyintherelativitychapter(Chapter36).Relativityisusefu

7、lbutnotessentialforthischapter.IfyouskippedChapter36,you’llwanttointroduce2E=mcandgiveashortdiscussionastowhatitmeans.Massesinthischapterare2frequentlygivenasMeV/c,sostudentswillneedtoknowwhatthismeansandhowtouseit.Nuclearphysicsrequiresextraattentiontosignificantfiguresb