Magnetic moments of neutron-rich nuclei $^{30}$Al and $^{32}$Al

The magnetic moments of the ground-state $^{30}$Al and $^{32} $Al have been measured by means of the $\beta$ ray-detected nuclear magnetic resonance ($\beta$-NMR) technique with spin polarized radioactive nuclear beams produced from projectile fragmentation reactions. The fragmentation processes that involved large numbers of removed nucleons, 10 and 8, from the $95$~MeV/u $^{40}$Ar projectile were successfully utilized to produce the polarized $^{30}{\rm Al}$ and $^{32}{\rm Al}$ fragments. A single-crystal corundum sample was employed as a stopper of the projectile fragments. The stopper temperature was maintained below $100$~K to preserve the spin polarizations during the $\beta$ decays. The quadrupolar splitting in the crystal was avoided by employing the ``magic angle'' technique. The magnetic moments have been successfully obtained, as $|\mu(^ {30}{\rm Al})|=(3.010\pm0.007)\mu_{\rm N}$ and $|\mu(^{32}{\rm Al})|=(1.959\pm0.009)\mu_{\rm N}$. Shell model calculations within the {\it sd} valence orbits using the USD interaction reproduced the both magnetic moments within $6$~\%. The border of the ``island of inversion'' will be discussed in comparison with the magnetic moments of $N=19$ isotones.