High-spin states of Tl187 populated in the Gd156(35Cl,4n) reaction have been investigated with -ray coincidence techniques. Two decoupled bands feeding the oblate 9/2- isomeric state have been established. These bands are built on h9/2 and i13/2 configurations associated with prolate shapes. The first observation of a low-K h9/2 structure in an odd-A Tl nucleus is used to draw conclusions on the role of this proton orbital in stabilizing the prolate minimum seen in light Hg isotopes
