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 oblate deformation with γ= -60°and probably originate from the four quasiparticle configurations πg_7/2 πh_11/2vh_11/2 vd_3/2 and πg_7/2πh_11/2 vh_11/2², respectively. These oblate bands exhibit strong M1 transitions, no signature splitting and different moments of inertia from those of prolate bands.