Interaction of 0.5- and 1.0-Mev Neutrons with Some Heavy Elements

The angular distributions of 0.5-Mev neutrons elastically scattered by Au, Bi, ${\mathrm{U}}^{238}$, ${\mathrm{U}}^{235}$, and ${\mathrm{Pu}}^{239}$ and of 1.0-Mev neutrons elastically scattered by the latter three materials have been measured. The differential and total elastic scattering cross sections, the elastic transport cross sections, and the inelastic collision cross sections are presented. Some theoretical angular distributions and cross sections based on a complex squarewell model for ${\mathrm{U}}^{238}$ are also included. The angular distributions of fission neutrons produced by 0.5- and 1.0-Mev incident neutrons are found to be isotropic, and the ratio of $\overline{\ensuremath{\nu}}({\mathrm{Pu}}^{239})$ to $\overline{\ensuremath{\nu}}({\mathrm{U}}^{235})$ is 1.3\ifmmode\pm\else\textpm\fi{}0.2 at both energies.