Weakly deformed oblate structures in 19876Os122

Gamma rays de-exciting isomeric states in the neutron-rich nucleus 198 76 Os 122 have been observed following relativistic projectile fragmentation of a 1 GeV per nucleon 208 Pb beam. The ground-state band has properties compatible with oblate deformation. The evolution of the structure of Os isotopes characterized by sudden prolate-oblate shape change is discussed and contrasted with the smooth change known in the Pt chain.