Calcium is a unique element, possessing two stable doubly-magic nuclei. Ca charge radii have been a challenge for nuclear theories to reproduce due to their unusual behavior. The chain of stable Ca isotopes spans from 40Ca to 48Ca, and although these differ by 8 neutrons, the nuclear charge radii are nearly identical. In addition to this peculiarity, there is a pronounced odd-even staggering in the charge radii, and an unexpected increase moving toward the neutron-rich isotopes. This work represents the first investigation of charge radii of these neutron-deficient calcium isotopes. Collinear laser spectroscopy (CLS) has been shown to be a valuable tool to investigate the fundamental properties of nuclei, such as nuclear spin, charge radii, magnetic dipole moments, and spectroscopic electric quadrupole moments. By probing the shift of the hyperfine spectra between isotopes, the nuclear charge radius can be extracted. In the case of non-zero nuclear and atomic spins, the nuclear magnetic dipole and electric quadrupole moment can also be obtained from the hyperfine splitting. In the present work, CLS was successfully performed on 36,37,38,39Ca at the BEam COoler and LAser spectroscopy (BECOLA) facility at the National Superconducting Cyclotron Laboratory (NSCL) at Michigan State University. Improvements to the offline ion source and laser system, and a new photon detection system made it possible to study 36Ca with only 500303 ions/s despite the challenge of the short 102 ms half-life, the most sensitive measurement at BECOLA to date. First measurements were made of the charge radii of 36-38Ca, and the charge radius of 39Ca is in agreement with previous results, while reducing uncertainty by a factor of 3. The charge radii of these isotopes, especially the weakly-bound 36Ca have required an advanced model of charge radii to understand the effects of loosely-bound protons on the pairing interaction, in the vicinity of the proton drip-line (35Ca is the last bound calcium isotope). Despite the fact that the protons in these neutron-deficient systems are weakly-bound, the charge radii of 36-38Ca were found to be very compact and significantly smaller than predicted by previous theories. With Nuclear Density Functional Theory (DFT) using a novel Fayans interaction which contains novel nuclear-density gradient dependent surface and pairing terms, the complete chain of charge radii of 36-52Ca have now been reproduced and understood, and the DFT model best describing these new measurements on the neutron-deficient side also has improved agreement with data on the neutron-rich side.
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