Abstract
We present a study of nuclear shape coexistence in the region of neutron-deficient lead isotopes. The midshell gold isotopes Au180,185,188,190 (Z=79), the two long-lived nuclear states in At197 (Z=85), and the neutron-rich nuclide At219 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 Au188,190. 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.
Highlights
The theoretical description of nuclear structure is made difficult by uncertainties in the modeling of the nucleon-nucleon interaction and by the sheer number of constituents of the atomic nucleus, making the problem too difficult to solve
The midshell gold isotopes 180,185,188,190Au (Z = 79), the two long-lived nuclear states in 197At (Z = 85), and the neutron-rich nuclide 219At were produced by the ISOLDE facility at CERN and their masses were determined with the high-precision Penning-trap mass spectrometer ISOLTRAP
Significant deviations from the atomic-mass evaluation were found for 188,190Au
Summary
The theoretical description of nuclear structure is made difficult by uncertainties in the modeling of the nucleon-nucleon interaction and by the sheer number of constituents of the atomic nucleus, making the problem too difficult to solve. It is still interesting to confront their predictions with experiment and check the internal consistency of their theoretical constructs such as nuclear shells and nuclear deformation outside their original domain of parameter adjustment Despite their lack of spectroscopic accuracy, mean-field or density-functional-type approaches [11] remain an interesting tool to track the changes in structure along isotopic or isotonic chains: One often encounters in midshell regions sudden changes in the trends of nucleon separation energies or mean-square charge radii, accompanied by a change of the spacing of the yrast level sequence towards the pattern of a quantum-mechanical rigid rotor [12]. Studies performed over the past three decades by different methods have revealed a rapid evolution of nuclear structure with proton number This is vividly illustrated by the nuclear charge radii in the region. The third section presents new Hartree-Fock-Bogoliubov (HFB) calculations and discusses in this framework the structure of nuclei in the neutron-deficient lead region
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