High-resolution laser spectroscopy of $^{27-32}$Al

Hyperfine spectra of Al27–32 (Z=13) have been measured at the ISOLDE-CERN facility via collinear laser spectroscopy using the 3s23p2P3/2o→3s24s2S1/2 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 Al29 and electric quadrupole moments of Al29,30. 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 with 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, which is consistent with earlier studies. Moreover, both the scale and trend of the charge radii appear to be very sensitive to the chosen interaction.