Giant dipole resonances in excited Er isotopes

The shape evolution of $^{160}\mathrm{Er}$ at high excitation energies was studied by measuring the giant dipole resonance following the heavy ion fusion reaction $^{19}$F${+}^{141}$Pr at excitation energies of 59.2, 61.2, 74.3, and 90.3 MeV. The data analysis yields prolate, oblate, and triaxial solutions and without theoretical systematics none of them can be ruled out. Detailed comparison with theoretical predictions favor the prolate solution with a deformation decreasing from \ensuremath{\beta}=0.28 at 59.2 MeV to 0.24 at 90.3 MeV. No phase transition from a prolate to an oblate deformation was found in the temperature range (T\ensuremath{\sim}1.1--1.5 MeV) covered by this experiment.