Magnetic dipole moments as a strong signature for $\alpha$-clustering in even-even self-conjugate nuclei

TL;DR

This paper explores magnetic dipole moments in even-even self-conjugate nuclei, revealing signatures of alpha-clustering through experimental data and lattice model analysis, highlighting the role of shell closures and neutron addition.

Contribution

It provides new insights into alpha-clustering signatures in nuclear magnetic moments and investigates discretization effects in lattice models of these nuclei.

Findings

Gyromagnetic factors of ${}^{44} ext{Ti}$ excited states are consistently around +0.5.

Adding neutrons alters the alpha-cluster signatures in magnetic moments.

Discretization effects in lattice models influence magnetic dipole moment calculations.

Abstract

We investigate the magnetic dipole moments in even-even self-conjugate nuclei from ${}^{12}\mathrm{C}$ to ${}^{44}\mathrm{Ti}$. For the latter, the measured gyromagnetic factors of excited states turn out to assume the same value of $g \approx + 0.5$ within statistical errors. This peculiar feature can be interpreted on the basis of collective excitations of $\alpha$-clusters. Analogously, the behaviour of the same observable is studied for all isotopes obtained by adding one or two neutrons to the considered self-conjugate nuclei. It is found that for the $N = Z + 1$ isotopes the $\alpha$-cluster structure hardly contributes to the observed negative g- factor value, corroborating molecular $\alpha$-cluster models. The addition of a further neutron, however, restores the original $\alpha$-cluster g-factors, except for the semi-magic isotopes, in which the deviations from $g \approx + 0.5$ can be associated with the relevant shell closures. Secondly, we analyze the same observable in the framework of a macroscopic $\alpha$-cluster model on a finite lattice of side length $L$. We focus on the discretization effects induced in the magnetic dipole moments of the $2_1^+$ and the $3_1^-$ states of ${}^{12}\mathrm{C}$ at different values of the lattice spacing $a$.