The many facets of superdeformation in dysprosium isotopes: Multi-band structures, shape-driving orbitals and identical bands
Abstract
This thesis reports on a detailed study of new properties of superdeformed (SD) nuclei near A $\sim$ 150. Using the Gammasphere array, three experiments were performed in which data of unprecedented sensitivity were obtained. A SD band of 18 transitions was discovered in $\sp{154}$Dy, extending the "island" of SD nuclei around $\sp{152}$Dy to N = 88. This result is surprising as the observation of superdeformation in this nucleus had not been predicted by any of the cranked mean field calculations. The band is "identical" to the yrast SD band in $\sp{152}$Dy and to band 3 in $\sp{153}$Dy. A configuration for the new band was proposed based on the behavior of the T$\sp{(2)}$ moment of inertia with rotational frequency. The microscopic structure of one-hole excitations (with respect to the doubly-magic $\sp{152}$Dy SD band) were characterized in the SD well of $\sp{151}$Dy, not only by determining the transition energies of 7 SD bands, but also by measuring the quadrupole moment (Q$\sb{o}$) of the 4 most intense bands with the Doppler-shift attenuation method. The Q$\sb{o}$ moments of the yrast SD bands in $\sp{151}$Tb and $\sp{152}$Dy were obtained in the same measurement, hereby reducing systematic errors due to uncertainties in stopping powers. Differences found in the Q$\sb{o}$ moments of the yrast SD bands are understood in terms of shape polarization effects by the high-N intruder orbitals. These differences are well reproduced by the most recent cranked-Strutinsky and cranked Hartree-Fock calculations. Several of the excited SD bands in $\sp{151}$Dy (bands 2, 3 and 4) are "identical" to the $\sp{152}$Dy yrast SD band. Of particular interest is a band with transition energies lying midway between the gamma-ray energies of the $\sp{152}$Dy SD band. The presence of such a band had been predicted in calculations based on the strong coupling model within the pseudospin coupling scheme. Variations in the measured Q$\sb{o}$ moments of bands 2-4 are, however, best accounted for in calculations which do not suppose the presence of this symmetry. The data imply that small, but non-negligible changes in deformation are involved in identical bands.
Degree
Ph.D.
Advisors
Grabowski, Purdue University.
Subject Area
Nuclear physics
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