We present the first laser spectroscopic measurement of the neutron-rich nucleus 68 Ni at the N = 40 subshell closure and extract its nuclear charge radius. Since this is the only short-lived isotope for which the dipole polarizability αD has been measured, the combination of these observables provides a benchmark for nuclear structure theory. We compare them to novel coupled-cluster calculations based on different chiral two-and three-nucleon interactions, for which a strong correlation between the charge radius and dipole polarizability is observed, similar to the stable nucleus 48 Ca. Three-particle-three-hole correlations in coupled-cluster theory substantially improve the description of the experimental data, which allows to constrain the neutron radius and neutron skin of 68 Ni.
We present the results of high-voltage collinear laser spectroscopy measurements on the 5 ppm relative uncertainty level using a pump and probe scheme at the transition of involving the metastable state. With two-stage laser interaction and a reference measurement we can eliminate systematic effects such as differences in the contact potentials due to different electrode materials and thermoelectric voltages, and the unknown starting potential of the ions in the ion source. Voltage measurements were performed between −5 kV and −19 kV and parallel measurements with stable high-voltage dividers calibrated to 5 ppm relative uncertainty were used as a reference. Our measurements are compatible with the uncertainty limits of the high-voltage dividers and demonstrate an unprecedented (factor of 20) increase in the precision of direct laser-based high-voltage measurements.
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