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Abstract

Hyperfine spectra of $^\text{27-32}$Al ($Z=13$) have been measured at the
ISOLDE-CERN facility via collinear laser spectroscopy using the $3s^23p\
^2\text{P}^\text{o} _{3/2}\rightarrow 3s^24s\ ^2\text{S}_{1/2}$ atomic
transition. For the first time, mean-square charge radii of radioactive
aluminum isotopes have been determined alongside the previously unknown
magnetic dipole moment of $^{29}$Al and electric quadrupole moments of
$^{29,30}$Al. A potentially reduced charge radius at $N=19$ may suggest an
effect of the $N=20$ shell closure, which is visible in the Al chain, contrary
to other isotopic chains in the $sd$ shell. The experimental results are
compared to theoretical calculations in the framework of the valence-space
in-medium similarity renormalization group using multiple sets of two and
three-nucleon forces from chiral effective field theory. While the trend of
experimental magnetic dipole and electric quadrupole moments is well
reproduced, the absolute values are underestimated by theory, consistent with
earlier studies. Moreover, both the scale and trend of the charge radii appear
to be very sensitive to the chosen interaction.