Evolution of shell structure in neutron-rich calcium isotopes

TL;DR

This paper uses advanced nuclear theory methods to study calcium isotopes, revealing insights into shell evolution, sub-shell closures, and deviations from simple models in neutron-rich calcium isotopes.

Contribution

It combines chiral effective field theory interactions with coupled-cluster calculations, including continuum effects, to accurately predict properties of calcium isotopes and explore shell structure evolution.

Findings

Ground-state energies match experimental data

Predicted weak sub-shell closure at 54Ca

Strong deviations from shell model in odd-mass isotopes

Abstract

We employ interactions from chiral effective field theory and compute the binding energies and low-lying excitations of calcium isotopes with the coupled-cluster method. Effects of three-nucleon forces are included phenomenologically as in-medium two-nucleon interactions, and the coupling to the particle continuum is taken into account using a Berggren basis. The computed ground-state energies and the low-lying 2+ states for the isotopes 42,48,50,52Ca are in good agreement with data, and we predict the excitation energy of the first 2+ state in 54Ca at 1.9 MeV, displaying only a weak sub-shell closure. In the odd-mass nuclei 53,55,61Ca we find that the positive parity states deviate strongly from the naive shell model.