Excitation energy dependence of neutron yields and fragment kinetic energy release in the proton induced fission of 233U and 238U

Abstract

Abstract The yields and energies of neutrons emitted from fission fragments of known mass were measured as a function of proton bombarding energy for 233 U and 238 U. The familiar sawtooth dependence of v , the number of neutrons emitted per fragment, on the fragment mass was found to be considerably washed out with increasing bombarding energy, with the depth of the minimum at A ≈ 132 decreasing more rapidly than that at A ≈ 80. As the bombarding energy is increased the yield of neutrons from the heavy fragment increases more rapidly than does that of the light fragment. The results are interpreted in terms of qualitative considerations on energy-apportionment between fragments at the time of scission. Structure in the variation of the total fragment kinetic energy with mass ratio was observed to decrease at higher bombarding energies. The nuclear level density parameter a of the final fragments has been obtained as a function of fragment mass from the neutron kinetic energy and yield data. The a -values are observed to increase for fragments near closed shells and to decrease for mid-shell fragments as the excitation energy is increased.