Search

High-spin states in the odd-odd nucleus La136, which is located close to the β-stability line, have been investigated in the radioactive-beam-induced fusion-evaporation reaction Sn124(N17,5n). The use of the radioactive beam enabled a highly sensitive and successful search for a new isomer [14+,T1/2=187(27) ns] in La136. In the A=130–140 mass region, no such long-lived isomer has been observed at high spin in odd-odd nuclei. The La136 level scheme was revised, incorporating the 14+ isomer and six new levels. The results were compared with pair-truncated shell model (PTSM) calculations which successfully explain the level structure of the πh11/2⊗νh−111/2 bands in La132 and La134. The isomerism of the 14+ state was investigated also by a collective model, the cranked Nilsson-Strutinsky (CNS) model, which explains various high-spin structures in the medium-heavy mass region. It is suggested that a new type of collective structure is induced in the PTSM model by the increase of the number of πg7/2 pairs, and/or in the CNS model by the configuration change associated with the shape change in La136.