Lecture13-16

U the nuclear magneton is dened in terms of the

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Unformatted text preview: ms can bind into molecules. E) None of the above. 9 Atomic Mass Units u༇ 12C defined to be 12 units o  table of selected isotopes in the book Appendix B 10 12C Atomic Mass Units (u) and u༇  1 u is defined to be one twelRh the mass of Carbon 12. u༇  1u = 1.6606 X 10- 27 kg u༇  1u = 931.5 MeV/c2 o  that is the average mass of a nucleon bound inside 12C o  “typical” mass per bound nucleon u༇  Carbon 12 has 6 protons and 6 neutrons in the nucleus. u༇  The binding energy of 12C is 92.16 MeV, about 7.67 MeV per nucleon. 11 Nuclear Spin and Magne;c Moment u༇  Protons and neutrons are spin ½ o  but they have internal structure and are not point par;cles o  they are composed of quarks bound together by the real strong interac;on u༇  They have magne;c moments coming from the quarks with some correc;ons. u༇  The Nuclear Magneton is defined in terms of the proton mass and is much smaller than the Bohr Magneton. u༇  µproton = 2.79 µn u༇  µneutron = - 1.91 µn 12 Nuclear Magne;c Resonance u༇ Apply Large B field u༇ Excite upper state with EM wave u༇ Detect transi;ons back down to lower state 13 14 Nuclear Shell Model u༇  Closed shells with large energy gaps for either p or n at 2,8,20,28,50,82,126 o  Nucleus more ;ghtly bound if either N or Z is one of these numbers u༇  u༇  u༇  u༇  Closed shells are spherically symmetric. Simple states near closed shells. Nuclear shell model usually gives the best understanding of nuclear states. Maria Mayer got Nobel prize for nuclear shell model. 15 Shell Model u༇  Maria Goeppert- Mayer won the Nobel prize with Hans Jensen in 1963. u༇ She came to UCSD at its beginning (from Univeristy of Chicago), geNng her first faculty job. 16 Binding Energy u༇ All nuclei have mass less than the sum of their parts. u༇ The protons and neutrons are bound together. u༇ We can compute the binding energies from the masses but we need highly accurate numbers. 17 Example: Binding Energy of Helium u༇ B.E. = 2mH + 2mn – MHe u༇ Go to Appendix B o  B.E. = 2(1.007825) + 2(1.008665) – 4.002603 o  B.E. = 0.03038 u (931.494013 MeV/u) = 28.3 MeV o  = 7.07 MeV per nucleon 18 Deuteron Harold Urey discovered Deuterium and worked on Tri;um. Is UCSD Harold amed dRer the 3H nucleus? really n Urey a iscovered Deuterium and worked on Tri;um. Is UCSD really named aRer the 3H nucleus? 19 Example: Fission Reactors and Atomic Mass Units (u) u༇ 235U+n - > 140Ce+94Zr + 2n + E u༇ 140Ce m=139.9054 u u༇ 94Zr m=93.9063 u༇ 235U m=235.0439 u༇ n m=1.0086 u u༇ How much Energy is released per U atom? 20 Trend in Binding Energy u༇  21 Binding Energy per Nucleon u༇ Lowest energies around 56Fe. u༇ Biggest...
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This note was uploaded on 02/24/2014 for the course PHYS 2D taught by Professor Hirsch during the Winter '08 term at UCSD.

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