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CU-Boulder PHYS 3070 - The Nucleus

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http://physics.colorado.edu/phys3070The nucleusUnits of Mass and EnergyThe playersThe playersThe playersOther playersIsotopesCurve of Binding Energy - 1Curve of Binding Energy - 1Curve of Binding Energy - 2Curve of Binding Energy - 3Stable and unstableJudah Levine, 3070L20 1http://physics.colorado.edu/phys3070http://physics.colorado.edu/phys3070Judah LevineJudah LevineJILA SJILA [email protected]@colorado.edu303 492303 492--7785 (27785 (2--7785)7785)M,F 11M,F 11--Noon, W 1Noon, W 1--3 pm3 pmalso by appointmentalso by appointmentPower point files for all lectures Power point files for all lectures now on the course web pagenow on the course web pageJudah Levine, 3070L20 2The nucleusThe nucleus10-15m10-10mOrbital electrons play no role in nuclear interactionsJudah Levine, 3070L20 3Units of Mass and EnergyUnits of Mass and Energy1 electron-volt= 1 eV= 1.6×10-19joules1 million electron-volts= 1 MeV= 1.6×10-13joules1 atomic mass unit= 1 amu= 1.66×10-27kgMass of carbon atom = 12 amuJudah Levine, 3070L20 4The playersThe playersElectron, e-: charge= -1, mass=9.1×10-31kgPositron, e+: charge= +1, mass=9.1×10-31kgAlso called “β-ray:” β-and β+e++ e-= BANG!E=mc2Judah Levine, 3070L20 5The playersThe playersElectron, e-: charge= -1, mass=9.1×10-31kgPositron, e+: charge= +1, mass=9.1×10-31kgAlso called “β-ray:” β-and β+e++ e-= BANG!E=mc2Suppose 1 gram of material has 1020electrons.If they collide with an equal number of positrons,How much energy is released? A: 8×103joules D: 8.2 ×107joulesB: 8.2×106joules e: 1.2 ×1040joulesC: 1.64 ×107joulesJudah Levine, 3070L20 6The playersThe playersElectron, e-: charge= -1, mass=9.1×10-31kgPositron, e+: charge= +1, mass=9.1×10-31kgAlso called “β-ray:” β-and β+e++ e-= BANG!E=mc2Suppose 1 gram of material has 1020electronsIf they collide with an equal number of positrons,How much energy is released? joulesEE72831201064.1)103()101.9(210×=×××××=−Ans=CJudah Levine, 3070L20 7Other playersOther playersProton, p: charge= +1, mass=1.0073 amu= 1.672×10-27kg Neutron, n: charge= 0, mass=1.0087 amu= 1.674×10-27kgAbout 1836×Meα particle= 2P + 2N = helium nucleusγ ray= very short wavelength radiation < 0.001 nm, usually described by its energy in MeV. (E ~ 1/λ)Judah Levine, 3070L20 8IsotopesIsotopesHydrogen: 1P, 0N (+ 1 orbiting electron) 11H0Deuterium: 1P, 1N (+ 1 orbiting electron) 12H1Tritium: 1P, 2N (+ 1 orbiting electron) 13H2Isotopes: Same P, same orbiting electrons (same chemistry),same charges implies same electrical behaviordifferent N implies different massStable isotopes: H and DUnstable isotope: Tritium, radioactiveNucleus ejects something, orbiting electrons unaffectedJudah Levine, 3070L20 9Curve of Binding Energy Curve of Binding Energy --11The fusion reaction:Mass of light atom is less than sum of the parts:Mass of 2 protons = 2×1.0073=2.0146 amuMass of 2 neutrons= 2×1.0087=2.0174 amuSum = 4.0320 amuJudah Levine, 3070L20 10Curve of Binding Energy Curve of Binding Energy --11The fusion reaction:Mass of light atom is less than sum of the parts:Mass of 2 protons = 2×1.0073=2.0146 amuMass of 2 neutrons= 2×1.0087=2.0174 amuSum = 4.0320 amuMass of helium atom= 4.0016 amuDifference = 0.0304 amuMass equivalent = 5.05 ×10 -29kgEnergy equivalent = 4.54×10-12joules4 grams of helium (6×1023atoms)= 2.7×1012joulesEquivalent to 445+ barrels of oilJudah Levine, 3070L20 11Curve of Binding Energy Curve of Binding Energy --22The fission reaction:Mass of heavy atom is greater than sum of the parts:Stable Bismuth: 83P, 125N, 208 TotalUnstable Isotope: 83P, 129N, 212 TotalAlpha decay, half-life=3 hours:MeVHeThBi 09.6422088121283++=Judah Levine, 3070L20 12Curve of Binding Energy Curve of Binding Energy --33Cross-over between “light” atoms and “heavy” atomsat about iron: 2655FE29(26P, 29N, 55 Total)Judah Levine, 3070L20 13Stable and unstableStable and unstableAll nuclei with mass > 209 are unstableand are “naturally” radioactiveSome nuclei with mass < 209 are alsonaturally


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CU-Boulder PHYS 3070 - The Nucleus

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