Identification of Collective Oblate Bands in 138Ce

High spin states in 138Ce have been investigated following heavy-ion induced reactions carried out at the China Institute of Atomic Energy, Beijing. Two collective rotational bands were established for the first time. These two bands show oblatedeformation with γ = -60° and probably originate from the four quasiparticleconfigurations πg7/2 ⊗ πh11/2 ⊗ νh11/2 ⊗ νd3/2 and πg7/2 ⊗ πh11/2 ⊗ [νh11/2]2, respectively. These oblatebands exhibit strong M 1 transitions, no signature splitting and different momentsof inertiafrom those of prolatebands.