Doctoral Dissertations

Date of Award

8-2003

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Major

Physics

Major Professor

Witold Nazarewicz

Abstract

This dissertation presents a theoretical study of rotational configurations in nuclei away from the line of ,8-stability : i) systematics of highly-deformed nuclear systems with moderate proton excess in the A"' 130 mass region, with the lightest of them closely approaching the proton drip line, ii) neutron-rich 30, 32,34,36,38 Ne and 32,34,36,38,40 Mg nuclei, farthest away from the stability valley, with more than twice as many neutrons as protons. It uses successfully the mean-field approach for describing deformed nuclear states at high angular momenta, affirming that the self-consistent mean-field theories are well justified for use with a variety of different rotating nuclear systems, for which they offer significant predictive power. We present the first fully self-consistent global set of high-spin calculations in the A"' 130 superdeformed region, using two conceptually different mean field theories : the non-relativistic cranked Skyrme Hartree-Fock method with SLy4 effective interaction ( CSHF ) , and the cranked Relativistic Mean Field approach ( CRMF ) . The results for 183 bands in CSHF and 105 bands in CRMF are used as a platform for the verification of the validity of the additivity approach in the A�130 superdeformed region, providing computational infrastructure for extracting sets of effective single-particle quadrupole moments and angular momentum alignments, which can be used directly in experimental analyses. The high precision of the additivity approach, and the accumulated statistics in this systematics allows us to perform a comparative study among the two self-consistent models. Its success implies that the extreme shell model concept is well justified at high angular momenta. The provided effective single-particle values and relative total Routhians for the bands in the same nucleus allows experimentalists to calculate easily the expected deformations and alignments in superdeformed bands, and serve as guidelines for spectroscopical analyses. This dissertation includes for the first time also the quantitative impact of the effective values of q22 as corrections to the main effective quadrupole components q20 for the evaluation of the transition quadrupole moments Qt, allowing us to separate out the deformation components in this region known for its relatively well pronounced -y-softness. The results indicate that the single-particle alignments are robust quantities, not varying significantly among self-consistent models. The effective alignments in CSHF are overall different from the corresponding values of the single-particle alignments, indicating the importance of the shape polarization effects in the self-consistent mean field studies. The high precision of the additivity results gives reasons to believe that there is a conceptual universality in the self-consistent models for rotating superdeformed nuclei in the wider mass range A=128-160. Our investigation of the properties of the very neutron-rich Ne and Mg nuclei leads for the first time to a quantitative understanding of their possible rotational behavior. The results show that there are sound physical reasons preventing the weakly bound intruder neutrons from "breaking away" under the influence of Coriolis and centrifugal forces at high cranking frequencies, thus offering a possibility for observation of rotational bands. The expected effect of the variation of the neutron shell structure with neutron number, mainly influencing the position of the high-j unique-parity shell, is balanced by the fact that the Coriolis force mainly acts on the high-j orbitals, which are strongly localized within the nuclear volume. As a result, no strong isovector effects ( due to neutron halo or skin ) are to be expected at high spins; the proton and neutron deformations are very similar even at extremely high rotational frequencies. The results show that for these nuclei the root-mean-square radii for protons and neutrons remain constant or within a narrow interval throughout the cranking frequency range. This work also makes predictions for the extent of the neutron drip line in the even-even Ne-Mg region, presents the very first cranking calculations for rotational bands in halo/ skin nuclei, and discusses the structure of their yrast bands.

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