Isomerism in the south-east of 132Sn and a predicted neutron-decaying isomer in 129Pd

Excited states in neutron-rich nuclei located south-east of Sn-132 are investigated by shell-model calculations. A new shell-model Hamiltonian is constructed for the present study. The proton-proton and neutron-neutron interactions of the Hamiltonian are obtained through the existing CD-Bonn Gmatrix results, while the proton-neutron interaction across two major shells is derived from the monopole based universal interaction plus the M3Y spin-orbit force. The present Hamiltonian can reproduce well the experimental data available in this region, including one-neutron separation energies, level energies and the experimental B(E2) values of isomers in Sn-134,Sn-136,Sn-138, Cd-130, and Pd-128. New isomers are predicted in this region, e.g. in Sn-135, Cd-131, Pd-129, In-132,In-134 and Ag-130, in which almost no excited states are known experimentally yet. In the odd-odd In-132,In-134 and Ag-130, the predicted very long E2life-times of the low-lying 5(-) states are discussed, demanding more information on the related proton-neutron interaction. The low-lying states of In-132 are discussed in connection with the recently observed gamma rays. The predicted 19/2(-) isomer in Pd-129 could decay by both electromagnetic transitions and neutron emission with comparable partial life-times, making it a good candidate for neutron radioactivity, a decay mode which is yet to be discovered. (C) 2016 The Author(s). Published by Elsevier B. V. This is an open access article under the CC BY license.