Neutron and fragment yields in proton-induced fission of 238U at intermediate energies

The primary fission fragment mass and kinetic energy distributions, and neutron multiplicities as function of fragment mass have been measured in the proton-induced fission of U-238 at energies E-p = 20, 35, 50 and 60 MeV using time-of-flight technique. Pre-scission and post-scission neutron multiplicities have been extracted from double differential distributions. The fragment mass dependence of the post-scission neutron multiplicities reveals the gross nuclear shell structure effect even at the higher proton energies we measured. The yields of neutron-rich fission products in the fission of U-238 by 25 MeV protons were measured using an ion guide-based isotope separator technique. The results indicate enhancement for superasymmetric mass division at intermediate excitation energy of the fissioning nucleus, The experimental results have been analysed in the framework of a time-dependent statistical model with inclusion of nuclear friction effects in the fission process. (C) 2001 Elsevier Science B.V. All rights reserved.