Fission of Radium by 11- to 22-Mev Protons

The ranges and relative yields of ${\mathrm{Sr}}^{91}$ and ${\mathrm{Pd}}^{112}$ fragments from the fission of ${\mathrm{Ra}}^{226}$ by 11- to 22-Mev protons were determined by a radiochemical recoil-catching technique. The relative yield data indicate that above 11 Mev the three-humped mass-yield curve becomes predominantly "symmetric" and perhaps somewhat narrower. An apparent fission threshold of \ensuremath{\sim}10.4 Mev was observed. The curve of total fission yield vs energy has the same slope between 13 and 22 Mev as has been reported for the fast-neutron-induced fission of radium. The ranges in mg Au/${\mathrm{cm}}^{2}$ at 11 and 20 Mev, respectively, are, ${\mathrm{Sr}}^{91}$: 11.2\ifmmode\pm\else\textpm\fi{}0.9 and 10.8\ifmmode\pm\else\textpm\fi{}0.2; ${\mathrm{Pd}}^{112}$: 9.1\ifmmode\pm\else\textpm\fi{}1.0 and 9.2\ifmmode\pm\else\textpm\fi{}0.3, corresponding to an average total kinetic energy of 162\ifmmode\pm\else\textpm\fi{}10 Mev.