Transition from Prolate to Oblate to Triaxial Shapes in 15sYb

Abstract The decay of the entry states in ISIYb populated in the reactions of 149 MeV ,oNe with ,44Nd and lUNd has been investigated with a 4" multidetector system gated by a Ge counter. The average excitation energy, the ,.-ray spectra and the angular distribu tions as a function of multiplicity show several changes in the ,.-ray decay. These changes suggest a transition from prolate to particle aligned oblate connguration at low spin. At 1-38-48 collective transitions with dipole and quad rupole component possibly built on high K single particle states are observed. Furthennore, above 1-48 the dipole component disappears suggesting a further change toward more triaxial shape