Detailed band structures in A = 188-190 mercury isotopes: Superdeformation and other high-spin excitations
Abstract
In this work we present level schemes for the nuclei $\sp{188-190}$Hg, all of which have been extended considerably. Detailed cranked shell model calculations have been performed for all three nuclei considered. Based on the comparison of the results of these calculations with the experimental data, quasiparticle configurations are proposed for all observed rotational bands. In addition to extending many of the rotational bands to higher spins and excitation energies, we have also found structures characterized by irregularly spaced (in energy) transitions in $\sp{189,190}$Hg. These structures are interpreted as arising from the nuclei changing shape from oblate-collective to prolate-noncollective. This behavior is discussed in the context of band termination, and several candidates for terminating states are identified. The nucleus $\sp{188}$Hg is discussed within the context of the cranked shell model. This nucleus is one of very few where it is possible to test the applicability of the cranked shell model formalism to both oblate and prolate deformed rotational structures. The most noteworthy new feature to emerge from the data is a negative parity rotational sequence which becomes the yrast prolate structure at $\hbar\omega$ $\sim$ 0.3 MeV and is characterized by a large alignment (i $\sim$ 10$\hbar$) for a two-quasiparticle structure. We propose the $\pi(\lbrack 660\rbrack 1/2\lbrack 541\rbrack 1/2)$ configuration for this band on the basis of comparisons with neighboring nuclei and the results of calculations. The data presented have been obtained in a series of experiments designed to study superdeformation in the neutron-deficient isotopes. The nucleus $\sp{189}$Hg is established as the lower limit of the A $\sim$ 190 region of superdeformation. The first strong evidence for a band interaction between a superdeformed ground band and an excited band is given by a change in slope of ${\cal J}\sp{(2)}$ at $\hbar\omega$ $\sim$ 0.32MeV. The data here are compared with calculations as well as with other nuclei in the region. The role of quasiparticle alignments in the behavior of ${\cal J}\sp{(2)}$ in the A = 190 region is discussed.
Degree
Ph.D.
Advisors
Gramowski, Purdue University.
Subject Area
Nuclear physics
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