Slide 1Lightning ReviewAlpha DecayBeta DecayBeta Decay – Electron EnergyBeta DecayGamma DecayUses of Radioactivity29.5 Natural RadioactivityDecay Series of 232Th29.6 Nuclear ReactionsWhich of the following are possible reactions?Q ValuesProblem: nuclear reactionsSlide 15Threshold EnergyIf the Q value of an endothermic reaction is -2.17 MeV, the minimum kinetic energy needed in the reactant nuclei if the reaction is to occur must be (a) equal to 2.17 MeV, (b) greater than 2.17 MeV, (c) less than 2.17 MeV, or (d) precisely half of 2.17 MeV.Slide 18Processes of Nuclear EnergyNuclear FissionSequence of Events in FissionEnergy in a Fission ProcessIn the first atomic bomb, the energy released was equivalent to about 30 kilotons of TNT, where a ton of TNT releases an energy of 4.0 × 109 J. The amount of mass converted into energy in this event is nearest to: (a) 1 g, (b) 1 mg, (c) 1 g, (d) 1 kg, (e) 20 kilotonsChain ReactionNuclear ReactorBasic Reactor DesignSlide 271. The Big Question of Particle Physics…Slide 29Slide 30A 10,000,000.00 Swedish Kronor question: Where did all the antimatter go?What are the right degrees of freedom?What would be the modern picture?Modern understanding: the ``onion’’ pictureSlide 35Slide 36Slide 37Slide 38Slide 39Slide 40… same thing about the interactionsUnification of forcesSlide 43The Standard Model of Elementary Particle PhysicsConditions for baryon asymmetryCan Standard Model explain baryon asymmetry?Experimental methodsSlide 48Experimental Facilities IExperimental Facilities IIWhat do physics PhD’s do?1101/14/1901/14/19General Physics (PHY 2140)Lecture 38Lecture 38 Modern PhysicsNuclear and Particle PhysicsRadioactivityNuclear reactionsNuclear EnergyElementary particlesChapter 29-30http://www.physics.wayne.edu/~apetrov/PHY2140/2201/14/1901/14/19Lightning ReviewLightning ReviewLast lecture: 1.1.Nuclear physicsNuclear physicsRadiationRadiationReview Problem: Isotopes of a given element have many different properties, such as mass, but the same chemical properties. Why is this?AZX1/ 30r r A=3301/14/1901/14/19Alpha DecayAlpha DecayWhen a nucleus emits an When a nucleus emits an alpha particlealpha particle it loses two it loses two protons and two neutronsprotons and two neutronsN decreases by 2N decreases by 2Z decreases by 2Z decreases by 2A decreases by 4A decreases by 4SymbolicallySymbolicallyX is called the X is called the parent nucleusparent nucleusY is called the Y is called the daughter nucleusdaughter nucleusHeYX424A2ZAZ4401/14/1901/14/19Beta DecayBeta DecayDuring beta decay, During beta decay, the daughter nucleus has the same the daughter nucleus has the same number of nucleons as the parent, but the atomic number of nucleons as the parent, but the atomic number is one lessnumber is one lessIn addition, an electron (positron) was observed In addition, an electron (positron) was observed The emission of the electron is The emission of the electron is from the nucleusfrom the nucleusThe nucleus contains protons and neutronsThe nucleus contains protons and neutronsThe process occurs when a neutron is transformed into a proton The process occurs when a neutron is transformed into a proton and an electronand an electronEnergy must be conservedEnergy must be conserved5501/14/1901/14/19Beta Decay – Electron EnergyBeta Decay – Electron EnergyThe energy released in the decay The energy released in the decay process should process should almost allalmost all go to go to kinetic energy of the electronkinetic energy of the electronExperiments showed that Experiments showed that fewfew electrons had this amount of electrons had this amount of kinetic energykinetic energyTo account for this “missing” To account for this “missing” energy, in 1930 Pauli proposed the energy, in 1930 Pauli proposed the existence of another particleexistence of another particleEnrico Fermi later named this Enrico Fermi later named this particle the particle the neutrinoneutrinoProperties of the neutrinoProperties of the neutrinoZero electrical chargeZero electrical chargeMass much smaller than the Mass much smaller than the electron, probably not zeroelectron, probably not zeroSpin of Spin of ½½Very weak interaction with matterVery weak interaction with matter6601/14/1901/14/19Beta Decay Beta Decay SymbolicallySymbolically is the symbol for the is the symbol for the neutrinoneutrino is the symbol for the is the symbol for the antineutrinoantineutrinoTo summarize, in beta decay, the following pairs of To summarize, in beta decay, the following pairs of particles are emittedparticles are emittedAn electron and an antineutrinoAn electron and an antineutrinoA positron and a neutrinoA positron and a neutrinoeYXeYXA1ZAZA1ZAZn7701/14/1901/14/19Gamma DecayGamma DecayGamma rays are given off when an excited nucleus “falls” to a lower Gamma rays are given off when an excited nucleus “falls” to a lower energy stateenergy stateSimilar to the process of electron “jumps” to lower energy states and giving off Similar to the process of electron “jumps” to lower energy states and giving off photonsphotonsThe excited nuclear states result from “jumps” made by a proton or neutronThe excited nuclear states result from “jumps” made by a proton or neutronThe excited nuclear states may be the result of violent collision or more The excited nuclear states may be the result of violent collision or more likely of an alpha or beta emissionlikely of an alpha or beta emissionExample of a decay sequenceExample of a decay sequenceThe first decay is a beta emissionThe first decay is a beta emissionThe second step is a gamma emissionThe second step is a gamma emissionThe C* indicates the Carbon nucleus is in an excited stateThe C* indicates the Carbon nucleus is in an excited stateGamma emission doesn’t change either A or ZGamma emission doesn’t change either A or ZC*Ce*CB1261261261258801/14/1901/14/19Uses of RadioactivityUses of RadioactivityCarbon DatingCarbon DatingBeta decay of Beta decay of 1414C is used to date organic samplesC is used to date organic samplesThe ratio of The ratio of 1414C to C to 1212C is usedC is usedSmoke detectorsSmoke detectorsIonization type smoke detectors use a radioactive source to ionize the Ionization type smoke detectors use a radioactive