Statistical and preequilibrium gamma-ray emission in heavy ion reactions at 25 MeV/nucleon

We measured gamma-ray spectra in coincidence with charged particles for the reactions Ca-40+Ca-48,Ti-46 at beam energy of 25 MeV/nucleon. Events corresponding to reaction mechanisms from quasielastic to fusion were observed. In fusion and in inelastic reactions an enhancement in the gamma-ray spectra is present in the energy region around 10 MeV for the Ca-48 target with respect to Ti-46 data. The analysis of the gamma-ray spectra relative to Ca-48 and Ti-46 targets shows the persistence of the GDR up to an excitation energy around 4-5 MeV/nucleon for the mass region around 60. This result was obtained by including, in the statistical calculations, corrections due to the open decay channels, the mass dependence of the GDR parameters, and isospin effects.