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Presentation of the PhD thesis “Statistical properties in the quasi-continuum of atomic nuclei”

Presentation of the PhD thesis “Statistical properties in the quasi-continuum of atomic nuclei”. Ann-Cecilie Larsen May 20, 2008. The atomic nucleus. Quantum energy levels. Nuclear level density = number of energy levels within one energy unit. Decay probability.

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Presentation of the PhD thesis “Statistical properties in the quasi-continuum of atomic nuclei”

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  1. Presentation of the PhD thesis“Statistical properties in the quasi-continuum of atomic nuclei” Ann-Cecilie Larsen May 20, 2008

  2. The atomic nucleus Ann-Cecilie Larsen

  3. Quantum energy levels • Nuclear level density = number of energy levels within one energy unit Ann-Cecilie Larsen

  4. Decay probability • Transition between quantum levels • Fermi’s golden rule: • Gamma-ray transmission coefficients and strength functions i  f Giant dipole resonance, 98Mo Ann-Cecilie Larsen

  5. Applications • Nucleosynthesis in supernovae • Transmutation of nuclear waste Ann-Cecilie Larsen

  6. Motivation • Level density and gamma-ray strength function in medium-mass nuclei: 44,45Sc, 50,51V, 93-98Mo • Shell effects? • Decay probability in the quasi-continuum? Ann-Cecilie Larsen

  7. The Oslo Cyclotron Laboratory • Reactions: inelastic scattering (3He,3He’), and pick-up (3He,) • Low spin and high intrinsic excitation energy • CACTUS: 28 5”x5” NaI (~15% eff.) • Eight E-E Si particle telescopes Ann-Cecilie Larsen

  8. NaI(Tl) Si E-E telescope   3He 45o Target nucleus Particle-gamma coincidences Ann-Cecilie Larsen

  9. The Oslo method in a • Unfold -ray spectra • Apply first-generation subtraction method • Ansatz: decay probability(Ex-E)T(E) 44Sc Ann-Cecilie Larsen

  10. Quality of the extraction, 44Sc Ann-Cecilie Larsen

  11. Experimental level densities Ann-Cecilie Larsen

  12. Shell effects in the Mo isotopes Calc. from neutron res. data Back-shifted Fermi gas: Ann-Cecilie Larsen

  13. Comparison with theory, 51V • Fermi gas? Ann-Cecilie Larsen

  14. Thermodynamics Microcanonical vs. canonical ensemble Ann-Cecilie Larsen

  15. Microcanonical entropy Ann-Cecilie Larsen

  16. J  Combinatorial model • Combining all possible proton and neutron configurations • Nilsson energy scheme • BCS quasiparticles Ann-Cecilie Larsen

  17. Calculated level densities, average number of broken pairs Ann-Cecilie Larsen

  18. Parity asymmetry • Defining the parity asymmetry: Ann-Cecilie Larsen

  19. Experimental gamma-ray strength functions Ann-Cecilie Larsen

  20. Comparison with theory • Anomalous strength functions? TXL(E) = 2 E2L+1 fXL fXL(E) =E-(2L+1) XL(E)/D Assuming only dipole radiation: f(E)  T(E) / 2E3 Ann-Cecilie Larsen

  21. Papers included in the thesis Ann-Cecilie Larsen

  22. Highlights • The Oslo method works well for medium-mass nuclei • Pronounced shell effects • Single quasi-particle entropy constant, but vanish near shell closures • Enhancement of low-energy gamma decay probability established for all nuclei studied Thank you for your attention! Ann-Cecilie Larsen

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