GDR γ-ray decay in 156Dy∗ from regions selected on temperature and angular momentum

The strength distribution of the GDR built on highly excited states in a restricted temperature domain in 156Dy and 155Dy nuclei has been deduced by subtraction of γ-ray spectra obtained for the decay of 154Dy∗ and 156Dy∗ from regions selected on angular momentum. The resulting difference spectra have been analyzed within the statistical model. The results show a large deformation (|β| ∼ 0.51±0.29 and 0.35±0.14) for the angular-momentum regions with 〈J〉 ∼ 32h̵ at T ≈ 1.8±0.2 MeV and 〈J〉 ∼ 46h̵ at T ≈ 1.7±0.2 MeV, respectively, in satisfactory agreement with calculations performed in the framework of Landau theory of shape transitions and statistical fluctuations. The deduced centroid energies are in agreement with the systematics of the GDR built on the ground state. The width of the GDR shows a systematic increase with increasing temperature.