1Final Exam• Wed 3/18 from8:00am-11:00 WLH 2005 • Will cover all the course material includingthe last week• 25 questions –multiple choice.• You are allowed to bring 1sheet of paper with equations on both sides.• Bring a scantron form and a picture id.Nuclear FissionNuclear FusionNuclear energyEnergy consumptions vsgross national productEnergy Use USA Oil Production in the US has peakedWorld production is close to peaking2World Oil ResourcesAlternatives to oilCoalNuclear Energy FissionFusionHydroelectricWindSolarBiomassCurve of the Binding EnergyfusionfissionEnergy can be released by Fusion and FissionNatural radioactivityMany elements found in nature are unstable and decayemitting radioactivity. These include Uranium, 238U , Radon 224Ra and Potassium 40K. Carbon 14C, The half lives of natural radio-isotopes are long.Not useful as sources for power. Low Power output.Induced Nuclear reactionsCombining nuclei (Fusion)Neutron reactions (Fission)22 3111 11DD TH+⎯⎯→+1 235 141 92 1092 56 36 0nU BaKr3n+⎯⎯→++Can result in short half lives- fast reactions-high energy density+ Energy+ EnergyFission of UraniumFermi (1936) “Transuranium elements”FastneutronsuraniumFound induced radioactivityBombard uranium with neutronsparafilmNeutron Source(radon+Be)Slowneutrons3Fission of UraniumStrassman and Hahn (1939)1 235 141092 56n U Ba other _products+⎯⎯→+Irradiated Uranium with neutronsDetected BariumConclude Uranium nuclei splits into smaller fragments Liquid Drop model-1235 236092 92nU U+⎯⎯→⎯⎯→T1/2~10-12sBa + productsLise MeitnerExplained fission due to the instabilityof the higher larger nucleus.Nuclear Chain reactionChain Reactionbinding of 1 neutron releases ~3 neutrons Each neutron can initiate another reactionCritical Condition235UnnNuclear reactorReproduction constantK = no. of neutrons that produce a new fission event n238U235U(Capture)(Fission)(Escape)K=1 ( self –sustained reaction)nEnriched 235UNatural Uranium is a mixture of 235U (0.7%) and 238U(99.3%)238U is does not undergo the fission process but actsas an absorber for neutrons. (neutron capture)Most Uranium nuclear reactors use uranium enriched in235U. (2-3%)Nuclear weapons used highly enriched 235U. (~90%)Enrichment done by mass separation. Gaseous diffusionCentrifuge process.Laser separationCentrifuge separation of isotopescentrifugalseparationgaseous UF64Nuclear reactorfast neutrons mustbe slowed down to react efficiently.Moderator- slowsneutrons to thermalvelocities.Control rods- neutronabsorbers to control the level of neutronsCritical condition. – When each neutron released initiates a new reaction. Nuclear reactorPlutoniumPlutonium is a fissionable material created in a nuclear reactor.238 1 23992 0 94Un Pu2e−+⎯⎯→+239Pu can be made into nuclear bombs.Pu can be chemically separated from U in spent fuelrods from nuclear reactors. Nuclear FusionFusion of small nuclei releases energy22 3 111 2 022 3111 1123 4 111 2 0DD HenDD THDT Hen+⎯⎯→++⎯⎯→++⎯⎯→+Q= 3.27 MeVQ= 4.03 MeVQ=17.6 MeVNuclear Fusion+Z +Z~10-15 MRequirements for fusionHigh Temperatures (T~ 108K)High density (n) for long time (τ)Lawson Criterionnτ> 1014 s/cm3+Z +ZHigh energy required to bring charged nuclei close togethervPlasma FusionMagnetic Confinementlong timeslow densityPrinceton TokomakT~108KPlasma is a gas of ionized atomsHeated to high temperatureConfined by magnetic forces5Laser fusion-Inertial ConfinementShort timesHigh densityDeuterium pelletLawrence Livermore LabNova LaserProspects• Nuclear energy by fission is currently a source of much of the electrical power (~15% USA).• The problems with nuclear energy – Radioactive waste disposal– Atomic bomb threats• Nuclear fusion reactions promise an unlimited source of energy.– Controlled fusion reactions are not yet