Fragmentation, dissipative expansion, and freeze‐out in medium energy heavy‐ion collisions

The collision dynamics of 96Mo + 96Mo at 55 A MeV is simulated by solving numerically the Boltzmann‐Uehling‐Uhlenbeck (BUU) transport equation for the one‐body phase‐space distribution‐function of nucleons with and without Coulomb interaction. A scatter‐plot of the one‐body density distribution shows an initial compression, subsequent homogeneous expansion, a breaking into “fragments”, a very slow creeping expansion up to a freeze‐out and in the case of included Coulomb‐interaction a Coulomb‐explosion. In the calculation which included Coulomb‐interaction the overall shape of the ensemble of dense fragments is spherical. The fragments are created over the entire volume of the dense part of the source and not at the surface only. In the simulation without Coulomb interaction a doughnut‐like shape may develop.