Formation of Heavy Residues with A<90 in the Asymmetric Reaction of 20 AMeV

The cross sections and velocity distributions of heavy residues from the reaction of 20 AMeV Sn + Al have been measured at forward angles using the MARS recoil separator at Texas A&M in a wide mass range. A consistent overall description of the measured cross sections and velocity distributions was achieved using a model calculation employing the concept of deep-inelastic transfer for the primary stage of peripheral collisions, pre-equilibrium emission and incomplete fusion for the primary stage of more violent central collisions and the statistical model of multifragmentation (SMM) for the deexcitation stage. An analogous calculation employing the evaporation code GEMINI featuring the sequential binary decay could not reproduce the observed yields of the residues from violent collisions (A<90) due to different kinematic properties. The simultaneous character of the multifragmentation process leading to the observed residues from violent collisions is thus demonstrated.