Fission dynamics for capture reactions in Ni-58,Ni-64+Pb-208 systems: New results in terms of thermal energy and neutron multiplicity correlated distributions
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The neutron multidetector DeMoN has been used to investigate the symmetric splitting dynamics in the reactions Ni-58,Ni-64 + Pb-208 With excitation energies ranging from 65 to 186 MeV for the composite system. An analysis based on the new backtracing technique has been applied on the neutron data to determine the two-dimensional correlations between the parent composite system initial thermal energy (E-CN(th)) and the total neutron multiplicity (nu(tot)), and between pre- and post-scission neutron multiplicities (nu(pre) and nu(post), respectively). The nu(pre) distribution shape indicates the possible coexistence of fast-fission and fusion-fission for the system Ni-58 + (208)pb (E-beam = 8.86 A MeV). The analysis of the neutron multiplicities in the framework of the combined dynamical statistical model (CDSM) gives a reduced friction coefficient beta = 23 +/- (25)(12) x 10(21) s(-1), above the one-body dissipation limit. The corresponding fission time is tau(f) = 40 +/- (46)(20) x 10(...-21) s. (C) 1999 Elsevier Science B.V. All rights reserved.