Probing the $N = 14$ subshell closure: $g$ factor of the $^{26}$Mg(2$^+_1$) state

TL;DR

This study measures the $g$ factor of the first-excited state in $^{26}$Mg, providing evidence for the $N=14$ subshell closure and highlighting the importance of precise $g$-factor measurements in testing shell-model predictions.

Contribution

The paper presents a new high-velocity transient-field measurement of the $g$ factor in $^{26}$Mg, challenging previous values and supporting shell-model predictions with the USDB interaction.

Findings

$g$ factor of $^{26}$Mg's 2+ state is +0.86±0.10

Evidence for the $N=14$ subshell closure in magnesium isotopes

Implications for neutron $pf$ admixtures in even-even magnesium isotopes

Abstract

The first-excited state $g$~factor of $^{26}$Mg has been measured relative to the $g$ factor of the $^{24}$Mg($2^+_1$) state using the high-velocity transient-field technique, giving $g=+0.86\pm0.10$. This new measurement is in strong disagreement with the currently adopted value, but in agreement with the $sd$-shell model using the USDB interaction. The newly measured $g$ factor, along with $E(2^+_1)$ and $B(E2)$ systematics, signal the closure of the $\nu d_{5/2}$ subshell at $N=14$. The possibility that precise $g$-factor measurements may indicate the onset of neutron $pf$ admixtures in first-excited state even-even magnesium isotopes below $^{32}$Mg is discussed and the importance of precise excited-state $g$-factor measurements on $sd$~shell nuclei with $N\neq Z$ to test shell-model wavefunctions is noted.