The statistical gamma-ray decay of the GDR built on excited states in
Dy nuclei has been investigated for selected domains of angular moment
um up to about 70hBAR and temperatures in the range 1-2 MeV. The GDR s
trength distributions extracted from the data indicate large average n
uclear deformations (beta approximately 0.35) at high angular momentum
and average temperatures T greater-than-or-equal-to 1.5 MeV. This exp
erimental observation is supported by results from calculations in whi
ch 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 a
nd constant average deformations [beta] approximately 0.35.