Collective model description of transitional odd-A nuclei. (II). Comparison with unique parity states of nuclei in the A = 135 and A = 190 mass regions

Abstract

Recent experimental data on unique-parity spectra of odd-A nuclei in the A = 135 and A = 190 mass regions are compared in a systematic way with calculated energies and transition probabilities of a quasiparticle coupled to a rotating triaxial core. The comparison yields detailed evidence for triaxial shapes. Complex spectra of strongly coupled stucture as well as decoupled structure and various intermediate types are reproduced by the model with core parameters β and γ determined from neighbouring even nuclei. The coexistence of ΔI = 2 and ΔI = 1 band structures, seen in some of the experimental spectra, is explained as a consequence of the shape asymmetry. In the A = 190 region, the odd-A spectra confirm the existence of a gradual shape transition from prolate-type shapes (186Os, γ = 16°) to oblatetype shapes (198Hg, γ = 37°). Energies and lifetimes in A ≈ 135 nuclei reveal prolate triaxial shapes with γ-values in the range 20° < γ < 30°. Contrary to the expectation of very γ-soft, fluctuating shapes which is based on calculated collective potentials, the present work seems to indicate that a number of transitional nuclei may have rather stable triaxial shapes. © 1975.