Penning-trap mass spectrometry and mean-field study of nuclear shape coexistence in the neutron-deficient lead region

Abstract

We present a study of nuclear shape coexistence in the region of neutron-deficient lead isotopes. The midshell gold isotopes $^{180,185,188,190}\mathrm{Au}$ $(Z=79)$, the two long-lived nuclear states in $^{197}\mathrm{At}$ $(Z=85)$, and the neutron-rich nuclide $^{219}\mathrm{At}$ were produced by the ISOLDE facility at CERN and their masses were determined with the high-precision Penning-trap mass spectrometer ISOLTRAP. The studied gold isotopes address the trend of binding energies in a region of the nuclear chart where the nuclear charge radii show pronounced discontinuities. Significant deviations from the atomic-mass evaluation were found for $^{188,190}\mathrm{Au}$. The new trend of two-neutron separation energies is smoother, although it does reveal the onset of deformation. The origin of this effect is interpreted in connection to the odd-even staggering of binding energies, as well as theoretically by Hartree-Fock-Bogoliubov calculations including quasiparticle blocking. The role of blocking for reproducing the large odd-even staggering of charge radii in the mercury isotopic chain is illustrated.