Fission and Reaction Cross Sections in the Uranium Region with 4- to 12-MeV Protons

Fission fragment angular distributions have been measured with gold surface barrier detectors for proton-induced fission of ${\mathrm{U}}^{233}$, ${\mathrm{U}}^{234}$, ${\mathrm{U}}^{235}$, ${\mathrm{U}}^{236}$, ${\mathrm{U}}^{238}$, ${\mathrm{Np}}^{237}$, and ${\mathrm{Pu}}^{239}$. Absolute fission cross sections were determined for ${\mathrm{U}}^{233}$ and ${\mathrm{U}}^{238}$. The proton projectile energy range of 4-12 MeV was obtained with the Argonne tandem Van de Graaff. Over this energy range the fission cross section of ${\mathrm{U}}^{233}$ changed by a factor exceeding a million. Total reaction cross sections were calculated for the highly fissionable ${\mathrm{U}}^{233}$ target by applying small corrections (3 to 20%) for the spallation cross sections. These reaction cross sections are compared with theoretical values deduced from surface absorption optical-model calculations with parameters of Perey and Wilkins.