Recoil Studies of High-Energy Proton Reactions in Bismuth

The ranges in bismuth of ${\mathrm{Sr}}^{91}$, ${\mathrm{Ba}}^{129}$, and ${\mathrm{Ba}}^{133m}$ recoil fragments from bombardment of bismuth with protons of 50 Mev to 2.2 Bev have been measured. The kinetic energies of the fragments have been calculated from the measured ranges and other reported range-energy data for fission fragments. The kinetic energy of the strontium recoils for all energies, and that of the barium recoils up to 450 Mev, can be explained as resulting from high-energy fission where most of the mass of the target is divided between two heavy fragments. At 2.2 Bev, the kinetic energy of the bariums recoils is substantially smaller, consistent with a complimentary fragment of about 20 mass units.The energy deposition in the target nucleus for processes leading to strontium and barium nuclides was obtained from the ratio of recoils projected forward to those projected backward, and subsidiary calculations involving momentum and energy conservation. The calculated values of the energy deposited are substantially lower than the bombarding proton energies, and even somewhat lower than energy values calculated for production of the "fissioning nucleus" from radiochemical data.Recoil experiments on spallation products, bismuth, lead, and thallium, of masses 198 to 203, from high-energy proton bombardment of bismuth, indicate that thallium nuclides formed directly are produced in processes involving alpha-particle emission.