Systematic shell-model study on spectroscopic properties in the south region of $^{208}$Pb

Abstract

Background: The properties of nuclei located in the south region of 208 Pb are important for understanding the r-process nucleosynthesis. While some isomeric states and their spectroscopic properties have been investigated experimentally in neutron-rich Pb, Tl, and Hg isotopes recently, a large portion of the area still remains unreachable.Purpose: We aim to study the properties of nuclei in the south region of 208 Pb systematically, including the binding and excitation energies and electromagnetic properties, in order to predict unknown properties of these nuclei, such as isomerism, utilizing a theoretical model which describes the experimentally known properties precisely. We also address whether the N = 126 shell closure is robust or not when the proton number decreases from 208 Pb.Methods: We performed large-scale shell-model calculations with a new Hamiltonian suggested in the present work. The model space is taken as the five proton orbits within 50 < Z 82 and the thirteen neutron orbits within 82 < N 184. And one-particle one-hole excitation is allowed across the N = 126 gap. The Hamiltonian is constructed by combining the existing Hamiltonians, KHHE (with minor adjustment of its monopole part) and KHPE, and the monopole based universal interaction.Results: The shell-model results well reproduce the experimentally observed binding energies and spectroscopic properties, such as isomerism, core excitation, and electromagnetic properties. Some possible isomeric states in neutron-rich Pb, Tl, and Hg isotopes are predicted with transition energies and half-lives. The N = 126 shell gap is predicted to be robust from Z = 82 down to 68 with minor reduction. We also examine the effective charges and the quenching of the g factors suitable for this region by systematic comparisons between observed and calculated electromagnetic properties.Conclusions: A new Hamiltonian is constructed for nuclei in the south region of 208 Pb, which provides reasonable descriptions on various nuclear properties through comprehensive and systematic studies. The present Hamiltonian and discussions provide fruitful information for future measurements and theoretical investigations in this region, such as the recommended effective charges and g factors, the predicted binding energies, isomeric states, and core-excited states.