STUDY OF THE DECAY OF HOT NUCLEI FORMED IN LA-139-INDUCED REACTIONS AT E A=45MEV BY A HYBRID DYNAMICAL-STATISTICAL CALCULATION/

The reactions La-139 + Al-27 and La-139 + Cu-65 at E/A = 45 MeV have b een modeled by combining a Boltzmann-Nordheim-Vlasov dynamical model c alculation with a statistical sequential binary decay model code. For the reaction La-139 + Al-27, the major features of the experimental da ta are adequately described by the model calculations. These features include the inclusive fragment cross sections and the total charge and source velocity distributions of multiple fragment events. Other fine r features, such as charge-Dalitz plots and the branching ratios betwe en events of different multiplicity, are not reproduced by the calcula tion. The failure of the calculations is even greater for the reaction La-139 + Cu-65, in which only the source velocity distributions of mu ltiple fragment events are reproduced. Because the source velocity can be a measure of how much of the target is incorporated into the proje ctile in inverse kinematics reactions, this suggests that the earliest stages of the reaction, described by the dynamical calculation, are a dequately characterized by the model. It is the later stages of the re action, when fragments are emitted, where the model calculation appear s to fail. However, there are some indications that statistical decay in the reaction La-139 + Cu-65 has occurred, whether by sequential bin ary decays or some type of prompt multifragmentation.