Mapping the GDR Quenching in Nuclei of Mass $A=120$--132

A comprehensive study of the evolution of the GDR properties from E* = 150 MeV to E* = 430 MeV has been undertaken in nuclei of mass A = 120 divided by 132. The experimental investigation was performed using MEDEA detector. An onset of a quenching of the GDR gamma yield was found at E* = 270 MeV comparing the experimental gamma-ray spectrum with statistical model calculation. The quenching effect increases at E* = 330 MeV and is even more pronounced when the analysis is extended to higher excitation energies using data from previously performed experiments. The comparison with phenomenological models describing the quenching phenomenon gives a qualitative explanation for the effect but is not able to reproduce its detailed features as a function of excitation energy. A smooth cut-off approach describes reasonably well the progressive disappearance of the dipole strength, which occurs around 220-230 MeV excitation energy, and shows that the GDR quenching is a rather sharp effect.