Nuclear Charge Distribution in Fission: Fractional Yields of Krypton and Xenon Isotopes from Thermal Neutron Fission of U233 and Pu239 and from 14-MeV Neutron Fission of U235 and U238

Abstract

Measurements of fractional cumulative yields of ${\mathrm{Kr}}^{89}$ through ${\mathrm{Kr}}^{93}$, ${\mathrm{Kr}}^{95}$, and ${\mathrm{Xe}}^{137}$ through ${\mathrm{Xe}}^{144}$ from thermal neutron fission of ${\mathrm{U}}^{233}$ and ${\mathrm{Pu}}^{239}$ and of ${\mathrm{Kr}}^{91}$ through ${\mathrm{Kr}}^{93}$ and ${\mathrm{Xe}}^{138}$ through ${\mathrm{Xe}}^{141}$ from 14-MeV neutron fission of ${\mathrm{U}}^{235}$ and ${\mathrm{U}}^{238}$ have been made. These data and other published data show that isobaric charge dispersion for fission products with mass number 140 from thermal neutron fission of ${\mathrm{U}}^{233}$ and mass numbers 138 and 139 from 14-MeV neutron fission of ${\mathrm{U}}^{238}$ is consistent with the Gaussian curve determined for thermal neutron fission of ${\mathrm{U}}^{235}$. This curve is used to estimate empirical values of $Z_P$, the "most probable charge" for a beta-decay chain, from the experimental data. From the variation of $Z_P$ with fragment mass, it is indicated that there is a general deviation from unchanged charge distribution of ≈0.6 charge unit in favor of the light fragment for the four fission processes considered as well as for thermal neutron fission of ${\mathrm{U}}^{235}$.