Interpretation of the large-deformation high spin bands in selected A=158-168 nuclei

TL;DR

This paper analyzes high-spin rotational bands in selected A=158-168 nuclei using the CNS model, focusing on shape, alignment, and the effects of various approximations to better understand nuclear deformation at high angular momentum.

Contribution

It provides a detailed analysis of high-spin bands with a focus on the effects of approximations and the role of triaxial shapes, including the impact of hexadecapole degrees of freedom.

Findings

Negligible errors from off-shell matrix elements and shell cut-off approximations.

Full inclusion of hexadecapole degree of freedom significantly lowers total energy.

Band shape and alignment suggest rotation around the intermediate axis in 158Er.

Abstract

The high-spin rotational bands in 168Hf and the triaxial bands in Lu nuclei are analyzed using the configuration-constrained Cranked Nilsson-Strutinsky (CNS) model. Special attention is given to the up-sloping extruder orbitals. The relative alignment between the bands which appear to correspond to triaxial shape is also considered, including the yrast ultra-high spin band in 158Er. This comparison suggests that the latter band is formed from rotation around the intermediate axis. In addition, the standard approximations of the CNS approach are investigated, indicating that the errors which are introduced by the neglect of off-shell matrix elements and the cut-off at 9 oscillator shells (N_{max}=8) are essentially negligible compared to other uncertainties. On the other hand, the full inclusion of the hexadecapole degree of freedom is more significant; for example it leads to a decrease of the total energy of ~ 500 keV in the TSD region of 168Hf.