Zakopane 2026 Conference on Nuclear Physics

The calcium isotopic chain, anchored by the doubly magic nuclei $^{40,48}$Ca, provides an important benchmark for studies focused on nuclear structure properties. In this region, nuclei in the vicinity of these shell closures exhibit predominantly single-particle behavior governed by the occupancy of the $f_{7/2}$ orbital, while the addition or removal of protons and neutrons drives a gradual evolution toward increased correlations and the emergence of collectivity toward the mid-shell region. The study of isotones in this mass region therefore offers direct insight into the role of proton-neutron interactions and the robustness of shell closures[1].

In this contribution, we present complementary laser spectroscopy studies probing nuclear properties in the vicinity of calcium. Within this context laser spectroscopy is a powerful probe of nuclear structure, enabling high-precision determination of electromagnetic moments, changes in mean-square charge radii, and nuclear spins. Collinear laser spectroscopy with fluorescence detection has been performed at the IGISOL facility on ionic transitions in vanadium isotopes (Z=23). Building on successful offline tests[4], this work has developed into an experimental campaign on radioactive isotopes in the mass range $A=46$ to $52$, providing new insights into a previously poorly explored isotopic chain. In parallel, results from the Collinear Resonance Ionization Spectroscopy (CRIS) experiment at ISOLDE on neutron-rich argon isotopes (Z=18) are presented. These measurements extend previous studies[2,3] toward more neutron-rich systems, providing new data for $^{45,47,48}$Ar and probing the evolution of nuclear structure as protons are removed from the calcium core and neutrons populate the $pf$ orbitals.

In both experimental approaches, the studied isotopic chains extend beyond $N=28$, enabling a direct investigation of the persistence of the $N=28$ shell closure associated with the filling of the $\nu f_{7/2}$ orbital. Together, these studies provide a consistent picture of nuclear structure evolution in the calcium region, highlighting the interplay between single-particle behavior, shell evolution, and the emergence of collectivity as a function of proton number.

References:
[1] Á. Koszorús et al., Nuclear structure studies by collinear laser spectroscopy, Eur. Phys. J. A 60, 20 (2024).
[2] K. Blaum et al., Nuclear moments and charge radii of argon isotopes between the neutron-shell closures N=20 and N=28, Nucl. Phys. A 799, 30 (2008).
[3] A. Klein et al., Moments and mean square charge radii of short-lived argon isotopes, Nucl. Phys. A 607, 1 (1996).
[4] A. Karadimas et al., High precision measurements of the hyperfine structure of vanadium ions in the ultraviolet range, Sci. Rep. (2026).