Structure of the semi-magic 203Ir and 202Os nuclei

The internal structures of the semi-magic, neutron-rich N=126 nuclei, 203Ir and 202Os, were studied. The nuclei of interest were produced using relativistic-energy projectile fragmentation of a 208Pb beam at the GSI facility in Germany. Internal isomeric decays were investigated via delayed γ-ray spectroscopy. In 203Ir, four observed transitions were associated with parallel decay branches from an isomeric yrast 19/2+ state. An observed weak delayed γ ray in 202Os is discussed in connection with a predicted isomeric 10+ state. Spin and parity assignments were made by comparison of the experimental data with state-of-the-art shell model calculations using three different shell-model parametrisations. It was found that the two-body interaction implemented to reproduce isomeric decays of the less exotic 204Pt and 206Hg isotones was the only interaction that describes the present experimental data. The persistence of the isomeric states, and the reproduction of the structure of the most neutron-rich N=126 nuclei ever observed, indicates that the N=126 shell closure remains robust.