Speaker
Description
H. Heylen for the COLLAPS - IS613 collaboration
Collinear laser spectroscopy was performed on $^{26-32}$Al ($Z = 13$) at the COLLAPS experiment in ISOLDE-CERN. From the measured isotope shifts in combination with multiconfiguration Dirac–Hartree–Fock calculations of the atomic mass and field shift factor [1], the differences in mean-square charge radii along the Al isotopic chain could be extracted. These results will be compared to IM-SRG calculations, providing an interesting benchmark for charge radii of odd-Z, open shell nuclei in an ab-initio framework [2]. Additionally, our experiment allowed filling up the gap of missing nuclear moments of $^{29}$Al and $^{30}$Al.
During the experiment, special attention was paid to measurement of the hyperfine spectrum of the 0+ isomer in $^{26}$Al. Despite the low isomeric production yields and fully overlapping structure with the ground state, for the first time an experimental value (and uncertainty) of its mean-square charge radius could be established. This is necessary to put the uncertainty assessment on the isospin-symmetry breaking correction used in the extraction of V$_\text{ud}$ from the $0^+\rightarrow 0^+$ superallowed beta-decay data on solid experimental grounds. Furthermore, the difference in radius between the $T = 0$ (ground) state and $T = 1$ (isomeric) state in $N = Z$ nuclei has been shown to be a sensitive probe for proton-neutron pairing correlations [3]. $^{26}$Al is only the fourth case (and lightest one so far) for which this quantity is measured, and knowledge of its magnitude is important to better understand the phenomenon across the nuclear chart.
[1] L. Filippin, PRA 94, 062508 (2016)
[2] J. Holt, private communication (2017)
[3] M. Bissell, PRL 113, 052502 (2014)
