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Combinatorial nuclear level-density model

Description: A microscopic nuclear level-density model is presented. The model is a completely combinatorial (micro-canonical) model based on the folded-Yukawa single-particle potential and includes explicit treatment of pairing, rotational and vibrational states. The microscopic character of all states enables extraction of level distribution functions with respect to pairing gaps, parity and angular momentum. The results of the model are compared to available experimental data: neutron separation energy level spacings, data on total level-density functions from the Oslo method and data on parity ratios.
Date: January 1, 2008
Creator: Moller, Peter; Aberg, Sven; Uhrenhoit, Henrik & Ickhikawa, Takatoshi
Partner: UNT Libraries Government Documents Department

Chaos and structure of level densities

Description: The energy region of the first few MeV above the ground state shows interesting features of the nucleus. Beyond an ordered energy region just above the ground-state the dynamics changes, and chaotic features are observed in the neutron resonance region. The statistical properties of energies and wave-functions are common to all chaotic nuclei. However, if instead a global property, like the local level-density function is studied, strong structure effects emerge. In this contribution we discuss these two different facets of warm nuclei. In section 2 the onset of chaos with increasing excitation energy is discussed, with both experimental observations and proposed theoretical mechanisms as starting points. The structure of level densities in the same excitation energy region based on the two different starting points, is treated in section 3, where we give a short presentation of a newly developed combinatorial level-density modell. Some results from the model are presented and discussed. Two coexisting facets of warm nuclei, quantum chaos and structure of the level density, are considered. A newly developed combinatorial level-density model is presented, and the role of collective enhancements discussed. An example of extreme parity enhancement is shown.
Date: January 1, 2008
Creator: Moller, Peter; Aberg, Sven; Uhrenholt, Henrik & Ickhikawa, Takatoshi
Partner: UNT Libraries Government Documents Department

Beta-decay half-lives and beta-delayed neutron emisison probabilities of nuclei in the region A. 110, relevant for the r-process

Description: Measurements of the {beta}-decay properties of A {approx}< 110 r-process nuclei have been completed at the National Superconducting Cyclotron Laboratory, at Michigan State University. {beta}-decay half-lives for {sup 105}Y, {sup 106,107}Zr and {sup 108,111}Mo, along with ,B-delayed neutron emission probabilities of 104Y, 109,11OMo and upper limits for 105Y, 103-107Zr and 108,111 Mo have been measured for the first time. Studies on the basis of the quasi-random phase approximation are used to analyze the ground-state deformation of these nuclei.
Date: January 1, 2009
Creator: Moller, Peter; Pereira, J; Hennrich, S; Aprahamian, A; Arndt, O; Becerril, A et al.
Partner: UNT Libraries Government Documents Department