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1/5/16 NuclearForces NuclearFissionandFusion • Asnucleigetbiggertheelectricforce increasesduetoaddi6onalprotons.The strongnuclearforceweakensbecausethe protonsandneutronsgetfurtherapart. • Thenucleusbecomesunstablewhenthe strongnuclearforcecannolongerovercome therepulsiveelectricforce. • Protonsinnucleusareall posi6velychargessothey tendtorepeleachother duetotheelectricforces. • Strongnuclearforce: a?rac6veforcethatbinds protonsandneutrons together. Fission • Fission:SpliFngofthenucleusinto2smaller parts. • Fissionresultswhenlargenucleiarebombarded withneutrons. • Theaddi6onalneutronsmakesthenucleus unstableanditbreaksapartreleasinglarge amountsofenergy. 1 1/5/16 Conver'ngMassintoEnergy • Duringnuclearfission,averysmallpercentage ofthemass(0.1%)isconvertedintoenergy accordingtoEinstein’sequa6one=mc2. • Verysmallamountsofmasscanbeusedto producelargeamountsofenergy. • Toaccountforthemass-energyconversion,a modifiedconversionlawisused.Accordingto thelawofconserva6onofmassandenergy, thetotalamountofmassandenergyremains constant. • Nuclearweaponsaredesignedtoproduce uncontrollednuclearfission. – Allofthereleasedneutronsarefreetocause otherfissionsresul6nginafast,intensereleaseof energy. • Inanuclearpowerplant,thefissionreac6ons arecontrolledbyabsorbingsomeofthe neutronswithanon-fissionablematerial. ChainReac'ons • InthefissionofUranium-235,eachuranium nucleussplitsintotwosmallernucleiand2-3 neutrons. • Theneutronsreleasedcantriggeraseriesof nuclearfissions. Fusion • Fusion:Processinwhichnucleiof2atoms combinetoformalargernucleus. • Asinfission,asmallamountofthereactantmass isconvertedintoenergy. – Theheatfromthereac6oncanthenbeusedto generateelectricalenergy. – Radioac6vewaste,isabyproductofnuclear powerplants. 2 1/5/16 Fusion • Fusionreac6onsarewhatoccursinthesun. • Fusionrequiresextremelylargetemperaturesto startthereac6onandatsuchhightemperatures ma?erexistsasplasma. – Plasma:stateofma?erinwhichatomsarestripped oftheirelectrons. • Fusioncouldpoten6allybeasourceofclean energy,butscien6stshavetofigureouthowto getthehightemperaturesthatarerequiredand howtocontaintheplasma. 3
