Gaussian Wave-Packet Dynamics with and without Correlations

Abstract

The theoretical description of heavy-ion collisions at intermediate beam energies, 10 MeV ≲, E/A ≲ 150 MeV, is still in an unsatisfactory state. Different factors contribute to that situation. Thus, for one, the nucleon excitation energies are low and in that comparable to nucleon localization energies, indicating a likely importance of the quantal effects. With the change in the beam energy in the discussed range, the dynamics changes from that dominated by the mean field to that dominated by collisions (as evidenced in the appearance of the flow balance-energy). As excitation energies grow, they begin to exceed the average binding energies per nucleon and, within the mentioned range of E/A, a massive production of intermediate-mass fragments (IMF) takes place[1]. The production, in terms of IMF multiplicity or total mass that IMF carry, maximizes at E/A ~ 75 MeV. The description of the intermediate and light fragment production is beyond the capability of common single-particle models of collisions[2]. The single-particle models with fluctuating forces[3,4] can describe fragment production, but miss the shell effects and the discreteness of the mass and charge numbers. The involved limitation is recognized once one realizes that, in the very central Au + Au collisions at 100 MeV/nucleon, the probability for a proton to come out from the reaction as a constituent of an a particle is close[5] to 50%. Within the Boltzmann-Langevin model with the fluctuating forces[3,4], the α particle plays no distinguished role. Statistical models[6,7] account for the shell effects, but miss the reaction dynamics. The importance of the dynamics is seen, in particular, in the fact that the collective outward flow energy in the reactions is comparable to the thermal energy.