Coupled-channel description for mirror mass-11 nuclei compared to shell-model structures

TL;DR

This paper uses a coupled-channel approach with a shell-model comparison to analyze the complex spectra of mass-11 mirror nuclei, highlighting the importance of strong vibrational couplings in their structure.

Contribution

It introduces a combined MCAS and shell-model framework to describe mass-11 nuclei, emphasizing the role of collective couplings in their spectral properties.

Findings

Strong coupling of 2+_1 state in 10Be influences 11Be ground state parity

Coupled-channel vibrational model is essential for accurate spectra

Shell-model results support the collective coupling approach

Abstract

The spectra of mass-11 nuclei are unusual, and so pose a challenge for theoretical models of their structure. The set of isobars range from being well bound to nucleon emission (11B,11C) through weakly bound (11Li, 11Be), with the former taking the form of a two neutron halo, to being proton unstable (11N,11O). A self-consistent approach to understand this set of nuclei is especially important as the mirror pair 11Be-11N exhibit a parity-inverted ground state compared to their neighbouring nuclei. Herein the Multi-Channel Algebraic Scattering (MCAS) method has been used to describe the low excitation spectra of those isobars in terms of nucleon-nucleus clusters. A collective model description of the low-excitation states of the mass-10 core nuclei has been used to form the coupled-channel interactions required in the method. For comparison, and to understand the underlying configurations, a shell model approach has been used to obtain those spectra with no-core (0+2+4)hw and (0+2)hw shell-model spaces for the mass 10 and mass 11 nuclei respectively.The results of the calculations suggest the need of a strong coupling in the collective coupled-channel vibrational model. In particular, the strong coupling of the collective 2+_1 state of 10Be to the valence neutron plays a decisive role in forming the positive parity ground state in11Be.