Date of Award

9-1998

Degree Type

Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Supervisor

J.C. Waddington

Abstract

When some nuclei are excited to tens of MeV above their ground state, with angular momenta so high that they are on the verge of fissioning, they can take on cigar-like shapes with axis ratios of 2 : 1, so-called superdeformed shapes. These superdeformed nuclei de-excite by the emission of cascades of γ rays (a superdeformed band). One of the most puzzling aspects of this emission is the phenomenon called ΔI = 4 bifurcation, or staggering, in which every second γ-ray energy in a given superdeformed band is shifted upward relative to the other energies in the band. Very little is known about this phenomenon, making a systematic investigation necessary. In this thesis, ΔI = 4 bifurcation has been studied in twenty-two bands in europium and gadolinium nuclei with mass numbers A near 150. The results obtained include the observation that the staggering patterns in three identical bands (bands with identical moments of inertia) are very highly correlated. This result seems to agree with what one might expect from a restrictive interpretation of the model of Hamamoto and Mottelson, and the staggering patterns in these three bands are used to constrain the model parameters for this triplet of bands. This systematic survey of ΔI = 4 bifurcation has been used to rigorously test the model of Pavlichenkov, and that of Hamamoto and Mottelson. It is demonstrated that neither of these models is capable of explaining the results presented. Finally, a statistical analysis of the staggering patterns presented in this thesis is proposed and carried out. This analysis underlines the highly non-statistical nature of the staggering phenomenon, but also emphasizes the importance of independent verification of these results.

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