Author's School

Graduate School of Arts & Sciences

Author's Department/Program

Physics

Language

English (en)

Date of Award

Summer 9-1-2014

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Chair and Committee

Demetrios G Sarantites

Abstract

The transition quadrupole moments, Qt, of rotational bands in the neutron-rich, even-mass 102-108Mo and 108-112Ru nuclei were measured with the Doppler-shift attenuation method. The nuclei were populated as fission fragments from 252Cf fission. The detector setup consisted of the Gammasphere spectrometer and the Hercules fast-plastic array. This allowed the measurement of asymmetric DSAM lineshapes at different Gammasphere detector angles with respect to the fission axis. The measurements typically covered the 6 to 16ћ spin range of the ground-state band and at least a strong transition in the γ band. At moderate spin, the Qt moments are found to be reduced with respect to the values near the ground states, the latter being reported in the literature.

An attempt has been made (by Afanasjev) to describe the data in the framework of cranked relativistic Hartree-Bogolyubov theory, and the results are reported in the present work as well as in a Physics Letters paper by Snyder et al. For 104Mo reliable predictions can be made. Here an oblate shape and a low-spin triaxial shape (deformation parameter γ~-44°), predicted to be favored in other theoretical calculations, are ruled out by the data. There is some indication for a gradual change, at higher spin, from an initially prolate shape to a triaxial shape in 104Mo. The Qt data for 106Mo and 110,112Ru support this picture. The challenge of theory to describe the Qt data is addressed, which has to do with the very γ-soft potential-energy surfaces.

As a byproduct of the Qt analysis (which requires the determination of the intensities of the feeding transitions), the transition intensities of many weak high-spin or non-yrast states have been determined. These previously unknown intensity data are also reported.

In the appendix, the results of an attenuation-coefficient analysis for γ-ray angular distributions (due to recoil-in-vacuum) in heavy Ba isotopes are reported. These results are from a separate project, though from the same data set.

Comments

Permanent URL: http://dx.doi.org/10.7936/K7CV4FVC

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