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Description
The region between the strongly deformed nuclei around the $Z \sim 40$, $N \sim 60$ mass region and the spherical Sn chain represents a rich testing ground for nuclear structure models, probing shell evolution and the interplay between single-particle and collective degrees of freedom, as well as phenomena such as shape coexistence. In this context nuclear magnetic dipole moments are sensitive probes of the single-particle nature of nuclear configurations, while electric quadrupole moments reflect the degree of nuclear deformation. The changes in mean square charge radii further provide information on the evolution of nuclear size across an isotopic chain. Laser spectroscopy experiments enable the extraction of all these observables, along with nuclear spins, for ground and isomeric states in a nuclear model-independent manner from the measurement of isotope shifts and hyperfine structures of the atomic spectra [1].
In this contribution, the results of first collinear laser spectroscopy studies performed on a series of neutron-deficient Rh isotopes will be presented. These isotopes are expected to exhibit a structural evolution from emerging collectivity in the mid-shell region towards sphericity approaching $^{95}$Rh at $N=50$, as evidenced by observations in the neighboring Ru and Pd isotopic chains [2,3].
The isotopes of interest were produced at the IGISOL facility, University of Jyväskylä, utilizing the ion guide method [4], essential for the successful production of refractory elements such as Rh. The isotope shifts and hyperfine structure parameters of ground and isomeric states between $^{95}$Rh and $^{104}$Rh were subsequently measured via collinear fluorescence laser spectroscopy[5]. These measurements provide the first determination of mean-square charge radii and nuclear moments of ground and isomeric states across this isotopic chain. Additionally, these results will contribute to resolve ambiguities in the spin assignments of $^{95m}$Rh, $^{98m,g}$Rh, $^{100m}$Rh, and $^{102}$Rh. The extracted nuclear observables will be compared with theoretical models describing single-particle configurations and shape transitions in the region.
[1] Yang, X., et al., Progress in Particle and Nuclear Physics 129 (2020) 104005.
[2] Geldhof, S., et al., Physical review letters 128.15 (2022): 152501.
[3] Maas, B., et al., Physical review letters 135.20 (2025): 202501.
[4] Moore, I. D., et al., Hyperfine interactions 223.1 (2014): 17-62.
[5] Koszorús, Á., et al., The European Physical Journal A 60.1 (2024): 20.