The evolution of nuclear moments and charge radii approaching 100Sn

In this work, the electromagnetic properties of the tin atom and its nucleus are systematically investigated in order to test our description of complex many-body quantum systems, such as bound electrons in the atom, and the protons and neutrons within the nucleus. The main motivation of this thesis is to investigate the evolution of nuclear electromagnetic properties (magnetic dipole moments, spin, electric quadrupole moments and charge radii) when neutrons are removed from the tin nucleus, towards 100Sn (N = Z = 50). This neutron-deficient nucleus (12 neutrons away from the lightest stable tin isotope) is expected to exhibit the extraordinarily rare property of having an equal number of protons and neutrons in doubly-magic (closed proton and neutron shell) configuration. Doubly-magic nuclei are more tightly bound than their neighbouring nuclei and provide valuable stepping stones for investigating the influence on nuclear structure properties when adding or removing nucleons (protons or neutrons). The tin isotopic chain is expected to have two doubly-magic nuclei, the neutron-deficient 100Sn (N = Z = 50) and neutron-rich 132Sn (N = 82, Z = 50). While the doubly-magic nature of 132Sn has been firmly established, the shell-closures at 100Sn have not yet been confirmed due to the low production yields of the neutron-deficient tin isotopes. Interestingly, measurements hint towards an increased softness to deformation when approaching 100Sn which questions the robustness of the shell closure. Additionally, the controversial level ordering of the two neutron shell model orbits above N = 50, labeled 2d5/2 and 1g7/2, further fuel the curiosity. Thanks to the highly sensitive Collinear Resonance Ionization Spectroscopy (CRIS) technique at ISOLDE-CERN, the above questions could be addressed in this work. Using the CRIS technique, laser spectroscopic measurements of the hyperfine structures and isotope shifts could be resolved in atoms containing tin isotopes artificially produced at ISOLDE, ranging from 124Sn down to 104Sn. In preparation for these measurements, resonance ionization schemes in atoms containing the stable tin isotopes were extensively investigated. These measurements combined with with state-of-the-art quantum chemistry calculations revealed the sensitivity of different atomic transitions in tin to the nuclear structure properties, such as the nuclear magnetic dipole and electric quadrupole moments as well as the changes in mean-square charge radii. This work reveal that the ground-state nuclear moments of 105Sn is in a good agreement with a sequential shell model filling of neutrons in the 2d5/2 orbital above 100Sn. An enhanced collectivity is observed when adding neutrons in the 1g7/2 orbital, which is suggested to originate from the strong proton-neutron correlations driving proton excitations across the Z = 50 shell gap. Furthermore, the changes in the mean-square charge radii along the tin isotopic chain reveal a new perspective of the N = 64 subshell closure when filling the 2d5/2 and 1g7/2 neutron orbitals. These results are compared with state-of-the-art many-body calculations using interactions founded on the fundamental description of the strong nuclear force, only constrained by nuclear properties of light nuclei A≤4. The presented comparison between experiment and theory highlight the incredible progress as well as the current limitations in our quest towards a fundamental description of nuclear structure.