GAMMA-DECAY OF THE GIANT-DIPOLE RESONANCE EXCITED BY 27.5 MEV A HE-4-INDUCED BREAK-UP FUSION REACTION IN DY ISOTOPES/

Charged-particle-gamma-ray coincidences were utilized to study He-4-in duced break-up fusion reactions on Tb-159 at 25.5 MeV/A beam energy. I n coincident gamma-ray spectra the electric giant dipole resonance (GD R) built on highly excited states in Dy isotopes was observed. A prono unced splitting of the GDR was evident at a nuclear temperature of T a lmost-equal-to 2 MeV which can correspond to different nuclear shapes. Consistent with available systematics a prolate deformation could be suggested in agreement with results obtained at lower T; however, the onset of a phase transition to an oblate shape cannot be excluded. The widths of GDR components, similar to the results obtained recently fr om incomplete-fusion reactions with heavy ions, are as small as those of the GDR built on the ground state.