Freezeout concept and dynamical transport model in intermediate-energy heavy-ion reactions

For the central collision events of Ca-40 + Ca-40, generated by an antisymmetrized molecular dynamics model in the intermediate energy range of 35 to 300 MeV/nucleon, the density and temperature of a fragmenting source have been extracted using a self-consistent method with the modified Fisher model. Rather flat density values, rho/rho(0) similar to 0.65 to 0.7, are evaluated at the incident energies studied, even though the maximum density of the system achieved during the collisions increases monotonically from rho/rho(0) similar to 1.3 at 35 MeV/nucleon to 1.8 at 300 MeV/nucleon. Flat temperature values of T similar to 5.9 to 6.5 MeV are also extracted in this incident energy range. These extracted values indicate that, in average, intermediate mass fragments are formed at a later stage when the hot nuclear matter reaches at a "freezeout" volume by the expansion, which is not assumed in any transport models, but assumed generally in statistical multifragmentation models. This is the first time to demonstrate quantitatively a direct connection between the freezeout concept and transport model simulations in a multifragmenting regime of heavy ion collisions.