Heavy residues with A < 90 from the asymmetric reaction of 20 A MeV Sn-124+Al-27 as a sensitive probe of the onset of multifragmentation
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The cross sections and velocity distributions of heavy residues from the reaction of 20 A MeV 124Sn+27 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 code) for the deexcitation stage. An alternative calculation employing the sequential binary decay (GEMINI code) could not reproduce the observed yields of the residues from violent collisions (A < 90) due to different kinematic properties. The success of SMM demonstrates that the heavy residues originate from events where a competition of thermally equilibrated fragment partitions takes place rather than a sequence of binary decays. 2003 Elsevier B.V. All rights reserved.