GDR GAMMA-RAY DECAY IN DY-156-ASTERISK 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 Dy-156 and Dy-155 nuclei has been deduced by subtraction of gamma-ray spectra obtained for the decay of Dy-154 and Dy-156* from regions selected on angular momentum. The res ulting difference spectra have been analyzed within the statistical mo del. The results show a large deformation (\beta\ similar to 0.51 +/- 0.29 and 0.35 +/- 0.14) for the angular-momentum regions with [J] simi lar to 32 ($) over bar h at T approximate to 1.8 +/- 0.2 MeV and [J] s imilar to 46 ($) over bar h at T approximate to 1.7 +/- 0.2 MeV respec tively, in satisfactory agreement with calculations performed in the f ramework of Landau theory of shape transitions and statistical fluctua tions. The deduced centroid energies are in agreement with the systema tics of the GDR built on the ground state. The width of the GDR shows a systematic increase with increasing temperature.