Precision determination of charge dispersion and distribution in the proton-induced fission of²³⁸U at 13.9MeV excitation

Abstract

By means of a gas-jet transport system and the ordinary radiochemical stacked-target technique incorporated with the Geγ-ray spectrometry, 126 product nuclides with half-lives ranging from seconds through a year were identified and their yields were determined in the proton-induced fission of²³⁸U at 13.9 MeV excitation. The charge dispersion width was determined for mass chains and concluded to be constant with 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 of²³⁵U and also consistent with values reported for proton-induced fission of²³⁸U. From the width thus obtained, we determined the most probable chargesZ _p for observed isobaric multiplets. Considering the pre-scission neutron systematics and an appropriate charge polarization between the complementary fragments we deduced from the obtainedZ _p the post-scission neutron numberν _post that turned out fairly consistent with Terrell’s neutron systematics for thermal-neutron-induced and spontaneous fission. Thus obtainedν _post enabled us in turn to derive equations describingZ _p as functions ofA. The obtained charge dispersion and charge distribution resulted in the mass-yield distribution resembling that of thermal-neutron fission.