Study of entrance channel effects in heavy ion induced fission reactions using light particle multiplicities

Abstract

Pre-scission neutrons and alpha particle multiplicites have been measured for the compound nucleus 210Po at an excitation energy of 61.1 MeV populated through the reaction 12C + 198Pt to understand the dissipation effects in the heavy-ion induced fusion-fission reactions. The measured multiplicities were used to extract the fission time for the reaction using statistical model code JOANNE2 by varing transient (and#964;tr) and saddle-to-scission (and#964;ssc) times. The finite value of fission time obtained indicates that the fission of 210Po CN is accompanied by dissipation effects. A comparison with total fission time of the 18O + 192Os reaction populating the same compound nucleus indicates the influence of entrance channel mass asymmetry on the fission time. The analysis of mass distribution and mass energy distribution of the fission fragments was also carried out to examine the contribution of non compound nuclear processes in the true fusion-fission events. This analysis shows that the system under study follows the fusion-fusion path leading to the symmetric fission fragments. Also, the dynamical model calculations from HICOL revels that 93% of fusion trajectories leads to the formation of fully equilibrated compound nucleus. Dependence of total fission time on excitation energy and entrance channel has been studied in a systematic way for compound nuclei in the mass region A gt 190 indicating that the fission time increases as we go from asymmetric to symmetric reaction in entrance channel. Also, the dynamical effects during the formation phase of CN must be taken into account to explain the difference in neutron multiplicities when studying the entrance channel effects. newline