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

TL;DR

This study uses collinear laser spectroscopy at ISOLDE-CERN to measure hyperfine spectra of aluminum isotopes, determining charge radii and moments, and compares results with advanced theoretical models to explore nuclear structure effects.

Contribution

First-time measurement of charge radii and moments of radioactive aluminum isotopes, revealing potential shell closure effects and testing nuclear theory predictions.

Findings

Charge radii suggest a shell closure at N=20 in Al isotopes.

Magnetic dipole and electric quadrupole moments are well reproduced trend-wise by theory.

Absolute moments are underestimated by current theoretical models.

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.