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1、1Innuclearphysics,nuclearfusionisanuclearreactioninwhichtwoormoreatomicnucleicollideataveryhighspeedandjointoformanewtypeofatomicnucleus・Duringthisprocess,matterisnotconservedbecausesomeofthematterofthefusingnucleiisconvertedtophotons(energy).Fusionistheprocessthatp
2、owersactiveor“mainsequenee”stars,2Themostimportantfusionprocessinnatureistheonethatpowersstars・Thenetresultisthefusionoffourprotonsintoonealphapartici巳withthereleaseoftwopositrons”twoneutrinos(whichchangestwooftheprotonsintoneutrons),andenergy,butseveralindividualre
3、actionsareinvolved,dependingonthemassofthestar.Forstarsthesizeofthesunorsmaller,theproton-protonchaindominates.Inheavierstars,theCNOcycleismoreimportant・Bothtypesofprocessesareresponsibleforthecreationofnewelementsaspartofstellarnucleosynthesis.2Thefusionoftwonuclei
4、withlowermassesthaniron(which,alongwithnickel,hasthelargestbindingenergypernucleon)generallyreleasesenergy,whilethefusionofnucleiheavierthanironabsorbsenergy・Theoppositeistrueforthereverseprocess,nuclearfission.Thismeansthatfusiongenerallyoccursforlighterelementsonl
5、y,andlikewise,thatfissionnormallyoccursonlyforheavierelements.Thereareextremeastrophysicaleventsthatcanleadtoshortperiodsoffusionwithheaviernuclei.Thisistheprocessthatgivesrisetonucleosvnthesis,thecreationoftheheavyelementsduringeventssuchassupernova.3Theoriginofthe
6、energyreleasedinfusionoflightelementsisduetoaninterplayoftwoopposingforces,thenuelearforcewhichcombinestogetherprotonsandneutrons,andtheCoulombforcewhichcausesprotonstorepeleachother.Theprotonsarepositivelychargedandrepeleachotherbuttheynonethelesssticktogether;demo
7、nstratingtheexisteneeofanotherforcereferredtoasnuclearattraction.Thisforce,calledthestrongnuclearforce,overcomeselectricrepulsioninaverycloserange.Theeffectofthisforceisnotobservedoutsidethenueleus,hencetheforcehasastrongdependenceondistance,makingitashort-rangeforc
8、e・Thesameforcealsopullstheneutronstogether;orneutronsandprotonstogether•⑷BecausethenuclearforceisstrongerthantheCoulombforceforatomicnucle
