Moments and Radii of exotic Na and Mg isotopes

TL;DR

This paper extends shell-model calculations to study ground-state properties, including radii and moments, of neutron-rich Na and Mg isotopes up to driplines, providing predictions and insights into their deformation and neutron skin thickness.

Contribution

It introduces a method to extract deformation parameters for Monte Carlo Shell Model eigenstates and applies it to predict radii and moments of exotic isotopes.

Findings

Good agreement with experimental data for radii and moments

Neutron skin thickness around 0.1 fm for N=20 isotopes

Radii increase due to deformation and neutron excitations

Abstract

The ground-state properties of neutron-rich exotic Na and Mg isotopes with even numbers of neutrons, N, are studied up to driplines. The shell-model calculations with an ab initio effective nucleon-nucleon interaction reported in [Tsunoda, Otsuka, Takayanagi et al., Nature 587, 66 (2020)] are extended to observables such as magnetic dipole and electric quadrupole moments, and charge and matter radii. Good agreements with experimental data are found, and predictions are shown up to driplines. A prescription to extract the deformation parameters for the eigenstates of Monte Carlo Shell Model is presented, and the obtained values are used to calculate charge and matter radii. The increase of these radii from the Droplet model is described as the consequences of the varying deformation of the surface and the growing neutron excitations or occupations in the pf shell, consistently with the dripline mechanism presented in the above reference. The neutron skin thickness is shown to be about 0.1 fm for N=20, which can be compared to the value for 208Pb in an A1/3 scaling. The relation of the neutron skin thickness to the electromagnetic moments is discussed for an exotic nucleus, 31Na.