High-spin states and isomers in 136137138Ce

High-spin states in 136137138Ce have been populated by (α, xn) reactions and studied using in-beam γ-ray spectroscopic methods. New features result from this investigation. Levels up to I = 15, 33/2 and 16 have been identified in 136137138Ce, respectively. In 136138Ce a 10+ isomer has been found which has probably a hsub(11/2) two-neutron-hole configuration. The level scheme for 137Ce shows a decoupled band structure different from that of the lighter odd-mass Ce nuclei, where perturbed rotational bands based on the hsub(11/2) neutron-hole state were reported. The energies of the 15/2- → 11/2-, 19/2- → 13/2- and 21/2sup((+)) → 19/2- transitions in 137Ce are similar to the 2+ → 0+, 4+ → 2+ and 5- → 4+ transition energies in 138Ce, and those of 12+ → 10+, 14+ → 12+ and 15 → 14+ in 136Ce. The level structure of these nuclei can be understood if a transition from prolate to oblate shape through a triaxial region occurs between 135Ce and 137Ce. Furthermore, in 136Ce a negative-parity band with even- and odd-spin members was established. In 138Ce the negative-parity states 7- and 5- were observed. (Auth.)