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Gamma-ray strength functions obtained with the Oslo method

DEPARTMENT OF PHYSICS UNIVERSITY OF OSLO. Gamma-ray strength functions obtained with the Oslo method. Ann-Cecilie Larsen July 8, 2008. Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio. Collaborators.

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Gamma-ray strength functions obtained with the Oslo method

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  1. DEPARTMENT OF PHYSICS UNIVERSITY OF OSLO Gamma-ray strength functions obtained with the Oslo method Ann-Cecilie Larsen July 8, 2008 Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  2. Collaborators • Oslo: A. Bürger, M. Guttormsen, S. Messelt, F. Ingebretsen, H. T. Nyhus, J. Rekstad, S. Siem, N.U.H. Syed, and H. K. Toft • Livermore National Lab.: U. Agvaanluvsan,L. Bernstein • North Carolina State University/TUNL: R. Chankova, G. E. Mitchell • Åbo Akademi University, Finland: T. Lönnroth • Ohio University: A. Schiller A. Voinov Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  3. Outline • Introduction & motivation • Oslo experiments • Gamma-ray strength functions, medium-mass nuclei • Gamma-ray strength functions, 116,117Sn • Summary & outlook Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  4. i  f Decay probability • Fermi’s Golden Rule: • Statistical decay: • Gamma-ray strength function: Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  5. Resonances • Giant electric dipole resonance • M1 spin-flip, E2 isoscalar • M1 scissors mode, E1 skin oscillation 117Sn(,xn) Lepretre et al NPA 219, 39 (1974). Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  6. Experiments at OCL • Selected reactions: (3He,3He’), (3He,), (p,p’), (p,t) ... • Low spin and high intrinsic excitation energy • CACTUS: 28 5”x5” NaI (~15% eff.) • Eight E-E Si particle telescopes Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  7. Particle - gamma coincidences NaI(Tl) Si E-E telescope   3He 45o Target nucleus Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  8. Coincidence matrices 44Sc, first-generation -rays 44Sc, unfolded Sn Sp Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  9. Extraction of level density and gamma-ray transmission coeff. The first-gen.-ray matrix P(E,E) is factorized according to P(E,E) (E-E)T(E) Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  10. Theoretical vs. experimental first-gen. spectra 50V 44Sc Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  11. Normalization Level density: Low E: discrete levels At Sn: neutron res. spacing  Slope and abs. magnitude Gamma-ray transm. coeff.: Total, average radiative width  at Sn Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  12. Gamma-ray strength functions, medium-mass nuclei From transmission coefficient to -ray strength function: TXL(E) = 2 E2L+1 fXL  fXL = TXL(E) / (2 E2L+1) Assuming dipole radiation is dominant: fE1+M1 = Texp(E) / (2 E3) Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  13. Comparison with models and photoabsorption data, 44Sc Photoabs. cross section to strength function: E1 strength, Kadmenski, Markushev and Furman model: M1 spin flip and E2 isoscalar (Lorentzians) Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  14. Is the up-bend structure dependent on excitation energy? 45Sc, first.gen. matrix Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  15. Gamma-ray strength functions, 116,117Sn Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  16. Comparison with models and microscopic calculations, 116,117Sn Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  17. Comparison with photoneutron cross-section data, 116,117Sn Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  18. Dependence on excitation energy? 116Sn, first.gen. matrix Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  19. E1 pygmy resonance, unstable Sn isotopes LAND group, GSI Measuring above the neutron separation energy Adrich et al.,PRL 95, 132501 (2005) 130Sn: 7(3)% of TRK sum rule 132Sn: 4(3)% of TRK sum rule Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  20. E1 pygmy resonance, stable Sn isotopes Nuclear resonance fluorescence (,’) Govaert et al., PRC 57, p. 2229 (1998) 116Sn:  B(E1) = 0.204(25) e2 fm2 124Sn:  B(E1) = 0.345(43) e2 fm2  ≈ 0.4–0.6% of TRK sum rule Oslo measurements: 116,117Sn: 16(7) MeV mb (QRPA) 17(7) MeV mb (GLO)  ≈ 1.0(4)% of TRK sum rule Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  21. Summary & outlook • Oslo experiments – level density & -ray strength function • Medium-mass nuclei: Enhanced strength at low -ray energies • 116,117Sn: functional form of a “pygmy” resonance • Future experiments: 90,92Zr, U, Th, Pd... • Upgrade of exp. setup: Silicon Ring (SiRi) particle detection system • NaI  LaBr3(Ce)? Many thanks for your attention! Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

  22. Preliminary data, 46Ti Level density Gamma-ray strength function Workshop on Statistical Nuclear Physics and Applications in Astrophysics and Technology, July 8-11 2008, Ohio University, Athens, Ohio

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