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The emission of intermediate-mass fragments in collisions of [sup 197]Au on [sup 197]Au was systematically studied over the range of incident energies from 40 to 150 A MeV using the 4π-multidetector INDRA and beams from the heavy-ion synchrotron SIS at GSI Darmstadt. The analysis was performed as a function of incident energy and of impact parameter, defined through the total transverse energy of light charged particles (Etrans 12, Z≤2). This observable was found to scale linearly with the collision energy up to a certain limit above which it saturates. Strong forward-backward asymmetries in the emission pattern with respect to the rapidities of the projectile and target residua were observed. Their possible relation to equilibration is discussed and interpreted in the framework of molecular dynamics and statistical multifragmentation models. Transverse velocities at midrapidity for peripheral collisions were found to show a surprisingly weak dependence on the incident energy. On the contrary, transverse velocities at midrapidity for central collisions showed a strong dependence on incident energy indicating an increasing importance of collective flow with increasing bombarding energy. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The influence of radial flow on nuclear multifragmentation is studied using Au+Au central collisions for incident energies between 40 and 100 MeV/A. Central collisions are selected via an impact parameter estimator defined by the transverse energy of light charged particles. At all energies, the fragment size distributions are studied using the Statistical Multifragmentation Model (SMM) in order to extract thermal excitation energies. The excess kinetic energies are analyzed via the hypothesis of a radial, self-similar, but non-isotropic flow. At the lowest energy, this flow is small with respect to the thermal energy whereas, at 100 MeV/A thermal and radial energies are of the same order. The nature and origin of the radial flow is discussed. A comparison with the predictions of the Quantum Molecular Dynamics code is presented. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]