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.
Highlights
Laser spectroscopy performed at radioactive ion beam facilities is a powerful technique to study isotopes all across the chart of nuclei [1]
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
We focus on the magnetic dipole moments μ, electric quadrupole moments Qs, and changes in mean-square charge radii, δ r2, of the ground states of the aluminum isotopes 27–32Al (Z = 13)
Summary
Laser spectroscopy performed at radioactive ion beam facilities is a powerful technique to study isotopes all across the chart of nuclei [1]. Not limited to (near-)magic nuclei, the VS-IMSRG technique allows the exploration of the microscopic origins of global features such as the driplines [12], new magic numbers [13], and Gamow-Teller quenching [14], or local features along an isotopic chain, e.g., odd-even staggering in binding energies and radii [15] or the development of E 2 strength [16,17]. These studies illustrate the importance of observables beyond binding energies to gain complementary insights in the validity of a theoretical approach.
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