Mixing of quasiparticle excitations and gamma-vibrations in transitional nuclei

TL;DR

This paper investigates the coupling of quasiparticle excitations with gamma-vibrations in transitional nuclei, revealing how specific band structures originate from triaxial deformations and shell filling effects using advanced shell model techniques.

Contribution

It introduces a multi-quasiparticle triaxial projected shell model approach to explain the nature of low-lying K=3 bands in transitional nuclei and predicts their dependence on shell filling.

Findings

K=3 band originates from triaxially deformed two-quasiparticle configurations.

The structure of the K=3 band depends critically on shell filling.

Neutron and proton configurations can cross gamma-vibrational bands at high spins.

Abstract

Evidence of strong coupling of quasiparticle excitations with gamma-vibration is shown to occur in transitional nuclei. High-spin band structures in [166,168,170,172]Er are studied by employing the recently developed multi-quasiparticle triaxial projected shell model approach. It is demonstrated that a low-lying K=3 band observed in these nuclei, the nature of which has remained unresolved, originates from the angular-momentum projection of triaxially deformed two-quasiparticle (qp) configurations. Further, it is predicted that the structure of this band depends critically on the shell filling: in [166]Er the lowest K=3 2-qp band is formed from proton configuration, in [168]Er the K=3 neutron and proton 2-qp bands are almost degenerate, and for [170]Er and [172]Er the neutron K=3 2-qp band becomes favored and can cross the gamma-vibrational band at high rotational frequencies. We consider that these are few examples in even-even nuclei, where the three basic modes of rotational, vibrational, and quasi-particle excitations co-exist close to the yrast line.