Fission and Total Reaction Cross Sections for 22-Mev Protons onTh232,U235, andU238

Abstract

Absolute excitation functions for ($p, f$) reactions in ${\mathrm{Th}}^{232}$, ${\mathrm{U}}^{235}$, and ${\mathrm{U}}^{238}$ were measured by radiochemical techniques; at 21.5 Mev, the cross sections are 0.83, 1.31, and 1.28 barns, respectively (\ifmmode\pm\else\textpm\fi{}15 percent in each case). Cross sections for ($p, \mathrm{xn}$) reactions in ${\mathrm{U}}^{238}$ were found to be quite small. The total reaction cross sections correspond to a nuclear radius of $(1.55\ifmmode\pm\else\textpm\fi{}0.1){\mathrm{A}}^{\frac{1}{3}}\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}13}$ cm. Some advantages of determining the nuclear radius by total reaction cross sections are pointed out, and the discrepancy between electromagnetic and nuclear determinations of the nuclear radius is discussed.