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Download OWLBook: Chapter 24: Nuclear Chemistry -   Chapter 24: Nuclear Chemistry Outline: Section 24.1 Nuclear Reactions 24.1a Nuclear vs. Chemical Reactions 24.1b Natural Radioactive Decay Reactions (reactions and penetrating power) 24.1c Balancing Nuclear

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  • OWLBook:Chapter24:NuclearChemistry

    Outline:

    Section24.1NuclearReactions

    24.1aNuclearvs.ChemicalReactions

    24.1bNaturalRadioactiveDecayReactions(reactionsandpenetratingpower)

    24.1cBalancingNuclearReactions

    Section24.2StellarNucleosynthesisoftheElements

    24.2aHydrogenBurning(regularandcatalytic)

    24.2bOtherFusionReactions

    24.2cNeutronAdditionBetaDecay

    Section24.3NuclearStability

    24.3aIsotopicAbundance

    24.3bCalculatingBindingEnergy

    24.3cBindingEnergyTrends

    24.3dPredictingRadioactiveDecayPaths

    Section24.4KineticsofRadioactiveDecay

    24.4aRadioactiveDating

    24.4bComplexDecayMechanisms

    Section24.5NuclearFission

    24.5aFissionReactions,PowerPlantsandBombs

    24.5bProductionofUraniumNuclearFuelandBombs

    24.5cProductionofPlutoniumNuclearFuelandBombs

    24.5dHowaNuclearPowerplantWorks

    Section24.6ImportantNuclearProcesses

    24.6aSmokeDetectors

  • 24.6bFoodIrradiation

    24.6cNuclearMedicine

    24.6dRadiationandDNADamage

    24.6eRadonintheHome

    Section24.1NuclearReaction

    IntroductoryText

    Yourstudyofchemistrytothispointhasbeenoverwhelminglybasedonthestudyoftheelectronsofatomsinteractwithotheratomstoformeverythingaroundus.Strikinglyabsentfromtheconversationtothispointhasbeenthenucleusoftheatomitsasifthenucleiarejustalongfortheride.Wediddiscussabouthowanatomgetsitsidentity(thenumberofprotons),andthatthereareisotopesofmostelements(versionsofanelementwithdifferentmassesduetomoreorlessneutronsinthenucleus).Wealsotalkedabouthow99.9+%ofthemassofanatombutlessthan0.00000000000001%ofitstotalvolumeisduetothenucleus.Asidefromthat,thenucleushasbeenconsideredaconstantthroughoutourstudyofchemistry.Thisisforagoodreason:mostofthetime,nucleiareperfectlystableanddonotchange.Thischapterexplorestherestofthetime,whennucleidoreactandundergochange.

    OpeningExploration:PenetratingPowerofRadiation(newvideobasedmodule)

    24.1aNuclearvs.ChemicalReactions

    Inanynormalchemicalreaction,electronsmovefromoneenvironmenttoanother.Almostallreactionsareaccompaniedbysomeenergybeingabsorbedorreleasedwhenthoseelectronsmovefromoneenvironmenttoanother.Inanuclearreaction,partsofthenucleuschangeorientationoridentity.Thesechangesarealsoaccompaniedbyanexchangeofenergywiththesurroundings.Thisissimilartonormalchemicalsystemsbutthescaleoftheenergyexchangedisnot.MostchemicalreactionsoccurontheorderofkJ/molofreaction,forexamplepropane,commonlyusedinbarbquegrillsandforhomeheating,releasesXXXkJ/molwhenburned,oraboutX.XkJ/g.ThereactionofUranium235,thefuelfor

    thefirstnuclearexplosion,released1.95x1010kJ/molor8.31x10

    7kJ/g.Thisis20,000xmoreenergyper

    gramofreactantthanwhatweconsideravigorouschemicalexplosion.Figure24.XXXillustratesthisdifference,showingtherelativeamountsofwaterthatcanbeboiledusingasinglegramofpropaneandasinglegramofthemostcommonlyusednuclearenergyprocess,U235fission.

    Figure24.XXXRelativeAmountofWater1gofFuelcanBoil

    pairofphotosshowingrelativeamountofwaterthatcanbeboiledwith1gofpropaneand1gU235

  • Anotheraspectofthisenergydifferenceisthetypesofelectromagneticradiationnuclearandchemicalreactionsemit.Justasthetransitionofelectronsfromoneenergyleveltoanotherinanatomisquantizedandoccurswiththetransferofaquantumofenergy,nucleonsexhibitasimilartransitioninthenucleus.Whenanexcitedstatenucleusrelaxestothegroundstate,ittoogivesoffaquantumofenergy.Whentheelectronsrelaxedwecouldseesomeofthosetransitionsasvisiblelightbecausetheywereinthevisiblespectrumabout1to3eV/photon.WhenthenucleusrelaxesthetransitionsareontheorderofMeV/photonormillionsofelectronvoltsperphoton.Wecallthesephotonsgammarays.Figure24.XXXElectromagneticSpectrum(takenfromChapter6,highlightvisiblevs.gammafrequencies)QuickCheckRoughlyhowmuchmoreenergyisreleasedwhenonemoleofU235undergoesfissionthanwhenonemoleofgasolineburns?a)10times b)100times c)1,000times d)10,000times e)100,000timesans:d

    Section24.1bNaturalRadioactiveDecayReactions(reactionsandpenetratingpower)

    Alphaparticleproduction:Anparticleisa nucleus.Manynucleithatareparticularlyheavy,andallthosebeyondBiontheperiodictableundergoemission.Everytimeanucleusemitsanparticleitlosestwoprotonsandtwoneutrons.

    Theheavieststableelementontheperiodictableis .Everyisotopepast ontheperiodictableisradioactiveandcandecaybyalphaemissiontolosemassandbecomestable.Thealphadecayofuraniumisshownbelow

    or ExampleProblem24.1.1AlphaDecayBetaparticleproduction:aparticleisanelectron.Thiselectronisgeneratedinthenucleuswhenaneutronisconvertedtoaproton, .Themassnumberofthenucleusdoesnotchangein

    thisprocess.Anexampleofabetaemitteris .Notetheperiodictableliststheaverageisotopic

    massofnaturallyoccurringCsis132.9amu.Thisgivesusacluethat hastoomanyneutronstobestable.

    24 He+2

    83209 Bi 83

    209 Bi

    92238 U 2

    4 He+2 + 90234 Th 92

    238 U + 90234 Th

    01n 1

    0 + 11p

    55137 Cs

    55137 Cs

    55137 Cs 1

    0 + 56137 Ba

  • ExampleProblem24.1.2BetaDecayPositronproduction:a+isanantielectron.Thisisourfirstexampleofantimatter.Anantielectronhasthesamemassasanelectronbutcarriesexactlyoppositechargetotheelectron,+1.Likebetaparticleproduction,positronproductionoccursinthenucleustobringthebalanceofneutronstoprotonsclosertothecenterofthezoneofstability.Inthecaseofpositronemissionthenucleuscontainstoofew

    neutronsforthenumberofprotons.Anexampleofapositronemitteris .NotetheperiodictableliststheaverageisotopicmassofnaturallyoccurringNaas22.99amu.Again,thisgivesusacluethat

    hastoofewneutronstobestable.Thiswouldshowupontherightsideoffigurexxx.

    Inorderforpositronproductiontooccurtheenergydifferencebetweentheparentanddaughternuclidemustbeinexcessof1.02MeV.Thisisduetothecostofproducingantimatter,whichalsomustobeyE=mC2.Thispositrondoesnotlivelonginaworldmadeofmatter.Whenapositroncomesincontactwithanelectron(itsmatteropposite)theyannihilateeachothergeneratingpureenergy.Thisenergyisusuallyemittedintheformoftwophotonseachhaving0.511MeVofenergytravelinginoppositedirectionstoobeyconservationlaws.Electroncapture:Oneofthefewinstanceswhereorbitalelectronsareinvolvedinanuclearreactionisinelectroncapture.Electroncaptureoccurswhenanucleushastoofewneutronsforthenumberofprotonspresent.Anexampleofthisdecaymodeisshownbelow:

    Theresultofthisreactionissimilartothatofpositronproduction,bothreactionsresultintheparentnucleiconvertingoneprotontoaneutron,therebyincreasingnuclearstability.Onemaindifferenceisthatinelectroncapturethereactioncanoccurwithlessthan1.02MeVofenergyinthetransitionbetweentheparentandthedaughterasnoantimatteriscreated.Forreactionsthatdohavethenecessaryenergytocreatepositronstheymaystilldecaybyelectroncapture.Mostnucleithathavetoofewneutronstobestabledecaybyamixtureofpositronproductionandelectroncapture.Aselectroncapturedecayrequiresthecaptureofanorbitalelectron,nucleiwithhigherZ(andthereforealsolarger#sofelectrons)haveincreasingproportionsofelectroncapturedecayoverpositronemission.Thisdecaymodeisalsooneofthefewdecaymodesthatareinfluencedbytemperatureorelectronicenvironmentofthenucleus(duetoitsrelianceoncapturingtheelectron).Whatwouldbethemostlikelyelectroncapturedbythenucleus?Thiscaptureleavesavacancyinanelectronorbitalthatgetsfilledbyanouterorbitalelectron.Whenthisoccursanxrayphotonisemitted.ExampleProblem24.1.3PositronEmissionandElectronCaptureGammarayproduction:Gammarayproductionoccurswhenanucleusisinanexcitedenergeticstate.Thisismostoftenthecasefollowinganothernucleareventsuchasoneofthedecaymodesdiscussed

    1122 Na

    1122 Na

    1122 Na 1

    0+ + 1022 Ne

    3783Rb +1

    0e 3683Kr

  • above.Winitiallyfo

    Themintisotopede

    ManynucproductioreactanttShieldingcommonparticlespenetratifastmovialsointerparticlesGammarwithmattshieldgamlevels.

    SectionChemicalproducts.nucleusdeachelembalancing

    Manynucequation

    ParticleProtonNeutronElectronAlphaBetaPositron

    ExampleP

    henanucleuormsametast

    thenotationecaystotheg

    clearreactionon.Noteingatoproduct,as

    gandpenetformsofionarethemostingacoupleiingelectronsractwithmatcantravelaraysarehighterandcantmmasources

    24.1cBalareactionsareBecausenorefineseachementpresent.gthemassand

    clearreactionbalancingiss

    Problem24.1

    sisexcitedittablenucleon

    oftheexcitedgroundstate

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    nsinvolveantsummarizedi

    Symbolpne+

    1.4

    canreleaseenofBa137.

    dstateofbarisotopebyre

    xcitedstatedaoductionneithyareleaseof

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    clearReacon,balanced.lprocessesdolancedchemuclearprocesofthespecie

    imatterorpanTable24.1.

    55137 Cs

    56137m Ba

    energybyem

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    aughtersthatherthemassenergyinthe

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    articleswitha

    Massn110400

    10 + 5

    137m

    a 56137 Ba +

    mittingaphoto

    ometastable.henergygam

    tdecaytothenumbernoraeformofaph

    particlesandwithmatterahtheyinteraetofpaper.Barticleandhdependingonafewmillimenocharge.Tnsitymateriaetersthickto

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    nganuclearr

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    + 00

    on.WhenCs

    .Thismetastammaray.

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    dgammaraysalittledifferectstronglywetaparticleshaveanegativntheirkinetimetersofplasTheyonlywealssuchasleaoreduceexp

    thereactantsnynuclei,andhesamenumeactionequa

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