Ground State Electromagnetic Moments of \(^{37}\)Ca

The hyperfine coupling constants of neutron deficient \(^{37}\)Ca were deduced from the atomic hyperfine spectrum of the \(4s~^2S_{1/2}\) \(\leftrightarrow\) \(4p~^2P_{3/2}\) transition in Ca II, measured using the collinear laser spectroscopy technique. The ground-state magnetic-dipole and spectroscopic electric-quadrupole moments were determined for the first time as \(\mu = +0.7453(72) \mu_N\) and \(Q = -15(11)\) \(e^2\)fm\(^2\), respectively. The experimental values agree well with nuclear shell model calculations using the universal sd model-space Hamiltonians versions A and B (USDA/B) in the \(sd\)-model space with a 95\% probability of the canonical nucleon configuration. It is shown that the magnetic moment of \(^{39}\)Ca requires a larger non-\(sd\)-shell component than that of \(^{37}\)Ca for good agreement with the shell-model calculation, indicating a more robust closed sub-shell structure of \(^{36}\)Ca at the neutron number \(N\) = 16 than \(^{40}\)Ca. The results are also compared to valence-space in-medium similarity renormalization group calculations based on chiral two- and three-nucleon interactions.