GDR dissipation and nuclear shape in hot fast-rotating Dy nuclei

The statistical gamma-ray decay of the GDR built on excited states in Dy nuclei has been investigated for selected domains of angular momentum up to about 70hBAR and temperatures in the range 1-2 MeV. The GDR strength distributions extracted from the data indicate large average nuclear deformations (beta approximately 0.35) at high angular momentum and average temperatures T greater-than-or-equal-to 1.5 MeV. This experimental observation is supported by results from calculations in which thermal shape fluctuations are taken into account around an oblate equilibrium deformation beta(eq) Although this equilibrium deformation increases with angular momentum, the calculations show rather large and constant average deformations [beta] approximately 0.35.