New short-lived isomer in Xe 128

A search for short-lived isomers in Xe128 has been conducted using the generalized centroid difference method applied to γ-ray spectra measured with high-purity germanium detectors. A lifetime of 2.8 (±0.8±0.5) ns has been extracted for the 6- state, and a shorter lifetime, of the order of one nanosecond, has been extracted for the 5- state. This results emphasize the possibility to measure lifetimes of the order of a few nanoseconds using arrays of germanium detectors in fusion-evaporation reactions. The obtained results reveal an unexpected hindrance of the 271-keV, 6-→5- transition, which points to predominant 1/2+[400] - 9/2-[514] and 3/2+[402] - 9/2-[514] Nilsson configurations of the bands built on the 5- and 6- states, respectively. The obtained results are supported by projected shell-model calculations, which nicely reproduce the bands built on the Kπ=5- and Kπ=6- states, under the assumption of an attenuated monopole pairing strength.