New Insights into Backbending in the Symmetry-adapted Framework

TL;DR

This paper investigates the backbending phenomenon in atomic nuclei using the symmetry-adapted framework, revealing that energy spectrum changes do not necessarily correspond to intrinsic deformation alterations.

Contribution

It provides new microscopic insights into backbending, showing the decoupling between energy spectrum features and intrinsic nuclear deformation.

Findings

Energy spectrum replicates backbending without deformation change.

$^{48}$Cr is spherical on average due to shape mixing.

No anomalous increase in moment of inertia observed.

Abstract

We provide new insights into backbending phenomenon within the symmetry-adapted framework which naturally describes the intrinsic deformation of atomic nuclei. For $^{20}\text{Ne}$, the canonical example of backbending in light nuclei, the ab initio symmetry-adapted no-core shell model shows that while the energy spectrum replicates the backbending from experimental energies under the rigid rotor assumption, there is no change in the intrinsic deformation or intrinsic spin of the yrast band around the backbend. For the traditional example of $^{48}\text{Cr}$, computed in the valence shell with empirical interactions, we confirm a high-spin nucleus that is effectively spherical, in agreement with previous models. However, we find that this spherical distribution results, on average, from an almost equal mixing of deformed prolate shapes with deformed oblate and triaxial shapes. Microscopic calculations confirm the importance of spin alignment and configuration mixing, but surprisingly unveil no anomalous increase in moment of inertia. This finding opens the path toward further understanding the rotational behavior and moment of inertia of medium-mass nuclei.