Fragment emission pattern in central and semi-central heavy-ion collisions

Event-by-event emission pattern of all charged fragments in central and semi-central, symmetric, semi-symmetric and asymmetric heavy-ion collisions at energies (50-220) A·MeV have been studied in nuclear emulsions. The most central collisions, selected by momentum-tensor elongation and multiplicity criteria, exhibit one single fused source. Collective flow in this source is observed in symmetric (Kr + AgBr) collisions and weakly indicated in semi-symmetric (Ar + AgBr) collisions. Semi-central events exhibit quasi-target, quasi-projectile and participant or incomplete fusion sources from which no or very weak flow signals are observed. The emission from these sources is described by a Coulomb explosion model except for the fact that sub-Coulomb barrier fragments are frequent.