Identification Of Collective Oblate Bands In Ce-138

High spin states in Ce-138 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 gamma = -60 degrees and probably originate from the four quasiparticle configurations pi g(7/2) x pi h(11/2) x nu h(11/2) x nu d(3/2) and pi g(7/2) x pi h(11/2) x [nu h(11/2)](2), respectively. These oblate bands exhibit strong M1 transitions, no signature splitting and different moments of inertia from those of prolate bands.