From last time…Atomic Quantum number summaryPowerPoint PresentationNa Optical spectrumHow do atomic transitions occur?Another possibility: Stimulated emissionLASERSlide 8Ruby laser operationGood description of atomChap 42: Nuclear PhysicsNeutrons and ProtonsCarbonQuestionIsotopesHeavy Water: deuterium oxideSlide 17Slide 18Nuclear ForceThe Strong Nuclear ForceEstimating the strong forceNuclear massesSlide 23Binding energySlide 25Binding energy/nucleonFission and fusionNuclear fusionWhat about different isotopes?Stability of nucleiRadioactive nucleiNuclear spinMagnetic resonance imagingSlide 34RadioactivityParticles in the nucleusPutting nucleons in the nucleusProton and Neutron statesPopulating nucleon statesOther helium isotopesRadioactive decayDiscovery of radioactivityDetecting radiationRadioactive tracersEnergy of nucleusStable and Unstable IsotopesSlide 47Different nuclear configurationsComparing the ‘old’ and ‘new’What is this nuclear force?EM force and Strong ForceNucleons are not fundamentalThe ‘new’ nuclear forceWhat makes a nucleus stable?Slide 55Slide 56Slide 57Binding energy of different nucleiFusion vs. fission 1)Visualizing a nucleusFour fundamental forcesNucleus bound very tightlyNuclear Binding EnergyNuclear binding energyNucleus propertiesSlide 66Even strongerThur. Dec 6, 2007 Phy208 Lecture 271From last time…•Hydrogen atom•Multi-electron atomsCourse evaluations next weekTues. Prof MontaruliThurs. Prof. RzchowskiThis week’s honors lecture: Prof. Brad Christian, “Positron Emission Tomography”Thur. Dec 6, 2007 Phy208 Lecture 272Atomic Quantum number summary•Hydrogen atom states–n: principle quantum number •Determines energy •(n=1, 2, 3…)– ℓ: orbital quantum number•Magnitude of orbital angular momentum•ℓ=0, 1, 2, … n-1–mℓ: orbital magnetic quantum number•Orientation of •mℓ = - , - + 1, … 0, … - 1, + ℓ ℓ ℓ ℓ–ms: spin quantum number•Orientation of• ms=-1/2, +1/2 € n, l , ml, ms( ) € L = h l l +1( ) € r L € Lz= mlh( ) € r S Sz= msh( )Thur. Dec 6, 2007 Phy208 Lecture 273Elements in same column have similar chemical propertiesThur. Dec 6, 2007 Phy208 Lecture 274Na Optical spectrumNa589nm, 3p -> 3s•11 electrons–Ne core = 1s2 2s2 2p6(closed shell)–1 electron outside closed shell Na = [Ne]3s1•Outside (11th) electron easily excited to other states.Thur. Dec 6, 2007 Phy208 Lecture 275How do atomic transitions occur?•How does electron in excited state decide to make a transition?•One possibility: spontaneous emission•Electron ‘spontaneously’ drops from excited state–Photon is emitted‘lifetime’ characterizes average time for emitting photon.Thur. Dec 6, 2007 Phy208 Lecture 276Another possibility: Stimulated emission•Atom in excited state.•Photon of energy hf=E ‘stimulates’ electron to drop.Additional photon is emitted,Same frequency, in-phase with stimulating photonOne photon in,two photons out:light has been amplifiedEBefore Afterhf=EIf excited state is ‘metastable’ (long lifetime for spontaneous emission) stimulated emission dominatesThur. Dec 6, 2007 Phy208 Lecture 277LASER: Light Amplification by Stimulated Emission of RadiationAtoms ‘prepared’ in metastable excited states…waiting for stimulated emissionCalled ‘population inversion’ (atoms normally in ground state)Excited states stimulated to emit photon from a spontaneous emission.Two photons out, these stimulate other atoms to emit.Thur. Dec 6, 2007 Phy208 Lecture 278Ruby Laser•Ruby crystal has the atoms which will emit photons•Flashtube provides energy to put atoms in excited state.•Spontaneous emission creates photon of correct frequency, amplified by stimulated emission of excited atoms.Thur. Dec 6, 2007 Phy208 Lecture 279PUMPRuby laser operationMetastable stateRelaxation to metastable state(no photon emission)Transition by stimulated emission of photonGround state1 eV2 eV3 eVThur. Dec 6, 2007 Phy208 Lecture 2710Good description of atom•Hydrogen atom: single electron orbiting around single positively-charged proton•Hydrogen atom can be in different quantum states, corresponding classically to different orbits.•Can also have more than one electron orbiting around the nucleus.•# of electrons determines the chemical properties, and hence the element.Thur. Dec 6, 2007 Phy208 Lecture 2711Chap 42: Nuclear Physics•Nucleus consists of protons and neutrons densely combined in a small space (~10-14 m)–Protons have a positive electrical charge–Neutrons have zero electrical charge (are neutral)–Neutrons & protons generically called ‘nucleons’•Spacing between these nucleons is ~ 10-15 m•Size of electron orbit is 5x10-11 m•Nucleus is 5,000 times smaller than the atom!NeutronProtonThur. Dec 6, 2007 Phy208 Lecture 2712Neutrons and Protons•Zero net charge -> # protons in nucleus = # electrons orbiting.•The number of electrons determines which element.–1 electron Hydrogen–2 electrons Helium–6 electrons Carbon•How many neutrons?Neutron: zero charge (neutral)Proton: positive charge (equal and opposite to electron)Thur. Dec 6, 2007 Phy208 Lecture 2713CarbonAnother form of carbon has 6 protons, 8 neutrons in the nucleus. This is 14C.•Carbon has 6 protons, 6 electrons (Z=6): this is what makes it carbon.•Most common form of carbon has 6 neutrons in the nucleus. Called 12CC126This is a different ‘isotope’ of carbonTotal # nucleons# protonsThur. Dec 6, 2007 Phy208 Lecture 2714QuestionHydrogen is the element with one electron. Which of the following is NOT the nucleus of an isotope of hydrogen?A. One protonB. One proton and one neutronC. Two protons and one neutronHydrogenDeuteriumTrituiumOne protonOne protonone neutronOne protontwo neutronsIsotopes of hydrogenThur. Dec 6, 2007 Phy208 Lecture 2715Isotopes•Isotopes: Nuclei with –same # protons, but–different # neutrons•12C and 14C have same chemical properties. –Both have 6 protons/6 electrons, same outer electron configuration–So both called carbon•But have different number of neutrons. –12C has 12-6 = 6 neutrons–14C has 14-6 = 8 neutronsThur. Dec 6, 2007 Phy208 Lecture 2716Heavy Water: deuterium oxideD2O: two 2H, one 16O bonded together$15 / cube!How much heavier is D2O than H2O?A. 5 %B. 10%C. 15%D. 50%Thur. Dec 6, 2007 Phy208 Lecture 2717Thur. Dec 6, 2007 Phy208 Lecture 2718Thur. Dec 6, 2007 Phy208 Lecture 2719Nuclear Force•So what holds the nucleus
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