Shape staggering of midshell mercury isotopes from in-source laser spectroscopy compared with density-functional-theory and Monte Carlo shell-model calculations

The neutron-deficient Hg isotopes have been a paradigm for nuclear shape coexistence. The ground states of these nuclei exhibit striking structural differences from the neighboring Pb isotopes, and are very challenging to study experimentally. Here, new state-of-the-art data extend information on the charge radii (and electromagnetic moments) to the lightest Hg isotopes ever measured using laser spectroscopy. The results suggest a sudden decrease in deformation for the lightest isotopes and an end to the region of ground-state shape staggering. These data provide constraints on future large-scale microscopic shell model and density functional calculations.