Evolution of shell structure at $\mathbf{N=32}$ and 34: Insights from realistic nuclear forces

TL;DR

This study uses advanced nuclear force models to analyze the evolution of shell structure at neutron numbers 32 and 34, revealing how different nuclear interactions influence magic numbers in exotic nuclei.

Contribution

It provides a detailed analysis of shell evolution at N=32 and 34 using realistic forces and the in-medium similarity renormalization group method, highlighting the roles of various nuclear interaction components.

Findings

Strengthening of N=34 subshell gap below calcium

Weakening of N=32 subshell gap below calcium

Exotic N=32 isotones show large deformation and coexistence of structures

Abstract

We investigated the evolution of shell structure at $N=32$ and 34 in neutron-rich nuclei beyond the stability line using realistic nuclear forces, employing the state-of-the-art valence-space in-medium similarity renormalization group method. The shell gaps are discussed from the excitation energies of the first $2^+$ states and the evolution of effective single-particle energies. We addressed different components of the nuclear interaction--central, spin-orbit, and tensor--and their roles in the development of shell gaps far from stability. The calculated results align well with the available experimental data and suggest a strengthening of the $N=34$ subshell gap and a weakening of the $N=32$ subshell gap below Ca. Additionally, the low-energy structures of the exotic $N=32$ isotones below Ca revealed that their ground states exhibit large deformation and coexist with a weakly deformed band at low excitation energy. The present work demonstrates essential components of the nuclear force in shaping magic numbers far from stability and provides deeper insights into the structure of exotic nuclei from the underlying nuclear forces.