High energy proton emission in heavy ion reactions close to the Fermi energy

The production mechanism of energetic protons has been investigated at 44 A MeV, for systems with different mass asymmetry, in an exclusive experiment performed with the MEDEA detector. The bulk of our data supports the hypothesis that in heavy ion collisions at intermediate energy the energetic protons are emitted as a consequence of nucleon–nucleon collisions in the pre-equilibrium stage of the reaction. The comparison with dynamical calculations points out that for symmetric and light systems the angular distribution is reminiscent of the elementary np scattering, thus indicating energetic protons from light and symmetric systems as good candidates to study the nuclear in medium effect. Protons with energy exceeding more than four times the incident energy per nucleon have been measured over a broad angular range.