PRECISION DETERMINATION OF CHARGE DISPERSION AND DISTRIBUTION IN THE PROTON-INDUCED FISSION OF U-238 AT 13.9MEV EXCITATION

By means of a gas-jet transport system and the ordinary radiochemical stacked-target technique incorporated with the Ge gamma-ray spectromet ry, 126 product nuclides with half-lives ranging from seconds through a year were identified and their yields were determined in the proton- induced fission of U-238 at 13.9 MeV excitation. The charge dispersion width was determined for mass chains and concluded to be constant wit h respect to the mass. The average of the deduced widths was 0.69+/-0. 04 charge unit which was just equal to that of thermal-neutron fission of U-235 and also consistent with values reported for proton-induced fission of U-238. From the width thus obtained, we determined the most probable charges Z(p) for observed isobaric multiplets. Considering t he pre-scission neutron systematics and an appropriate charge polariza tion between the complementary fragments we deduced from the obtained Z(p) the post-scission neutron number nu(post) that turned out fairly consistent with Terrell's neutron systematics for thermal-neutron-indu ced and spontaneous fission. Thus obtained nu(post) enabled us in turn to derive equations describing Z(p) as functions of A. The obtained c harge dispersion and charge distribution resulted in the mass-yield di stribution resembling that of thermal-neutron fission.