Transition between phenomena governed by the mean field and those governed by nucleon-nucleon collisions in the reaction 40 Ar + 68 Zn

Collisions between a Zn target and Ar of 14.6, 19.6, 27.6 and 35 MeV/nucleon incident energy cover part of the transition region between reaction mechanisms dominated by the mean field observed at low energy and those resulting from nucleon-nucleon interaction at high energy. Peripheral collisions in this reaction have been studied. Experimental energy spectra for ejectiles having nearly the projectile mass, have been reproduced using diffractional model calculations. The competition between fragmentation and transfer processes in the production of projectile-like fragments shows the persistance of collective effects. The heavy fragments emitted in central collisions have also been investigated. Fusion-evaporation and fusion-fission cross sections have been measured. Incomplete fusion is present at all the incident energies and becomes increasingly preponderant over complete fusion with increasing projectile energy. From comparison with other results, the momentum transfer appears to depend on the asymmetry of the system and on the projectile mass. Fusion disappears slightly above 35 MeV/nucleon which corresponds to a compound nucleus temperature of about 7 MeV. The characteristics of the charged light particles emitted in the reaction have been studied, and analyzed with several models: moving source, preequilibrium emission and coalescence model