Year of Publication

2014

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Arts and Sciences

Department

Chemistry

First Advisor

Dr. Steven W. Yates

Abstract

Nuclei at closed shells tend to be spherical and are well-described by the shell model, while those between closed shells are deformed and better described by collective models. The nuclei which are in transitional regions between spherical and deformed may be studied to gain insight into the nature of this transition. The stable isotopes of zirconium and xenon span such transitional regions and are the subject of this dissertation. Gamma-ray spectroscopy following inelastic neutron scattering has been performed on the stable isotopes of Zr as well as 132,134Xe at the University of Kentucky Accelerator Laboratory. Level lifetimes have been measured using the Doppler-shift attenuation method, which allow the determination of transition probabilities that are of utmost importance in elucidating the structure of these nuclei.

The lifetime measurements were the focus of the study of the Zr isotopes. Previously measured level lifetimes in 94Zr by our group were called into question by recent electron scattering experiments. This motivated a re-measurement of these lifetimes and led to a study of the role of the chemical properties of the scattering samples employed in the measurements. Various Zr-containing compounds were characterized with powder X-ray diffraction and scanning electron microscopy and were employed as scattering samples. These studies revealed the impact of using amorphous materials and those composed of small particles as scattering samples on the resulting lifetimes, and has important implications for future lifetime measurements employing the Doppler-shift attenuation method.

For the xenon experiments, highly enriched (>99.9%) 132Xe and 134Xe gases were converted to solid 132XeF2 and 134XeF2, and were used as scattering samples. The xenon isotopes have not been particularly well-studied as elemental targets are gases under ambient conditions, which introduces difficulties into the measurements. Much new information was obtained for these nuclei, including the placement of many new transitions and levels, and measurement of many new level lifetimes, allowing the determination of reduced transition probabilities. This additional information provided important insight into the structure of these two transitional nuclei.

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