Non-yrast nuclear spectra in a model of coherent quadrupole-octupole motion

TL;DR

This paper introduces a model of coherent quadrupole-octupole vibrations and rotations to describe non-yrast energy sequences with alternating parity in various even-even nuclei, successfully reproducing spectral structures and transition probabilities.

Contribution

The study presents a novel model that describes non-yrast alternating-parity spectra and predicts transition probabilities, extending understanding of quadrupole-octupole collective motion in nuclei.

Findings

Reproduces the structure of alternating-parity spectra.

Predicts B(E1) and B(E3) transition probabilities.

Provides estimations of the collective energy potential.

Abstract

A model assuming coherent quadrupole-octupole vibrations and rotations is applied to describe non-yrast energy sequences with alternating parity in several even-even nuclei from different regions, namely $^{152,154}$Sm, $^{154,156,158}$Gd, $^{236}$U and $^{100}$Mo. Within the model scheme the yrast alternating-parity band is composed by the members of the ground-state band and the lowest negative-parity levels with odd angular momenta. The non-yrast alternating-parity sequences unite levels of $\beta$-bands with higher negative-parity levels. The model description reproduces the structure of the considered alternating-parity spectra together with the observed B(E1), B(E2) and B(E3) transition probabilities within and between the different level-sequences. B(E1) and B(E3) reduced probabilities for transitions connecting states with opposite parity in the non-yrast alternating-parity bands are predicted. The implemented study outlines the limits of the considered band-coupling scheme and provides estimations about the collective energy potential which governs the quadrupole-octupole properties of the considered nuclei.