Energy Dependence of the Recoil Properties of Products from the Interaction ofU238with 0.45-11.5-GeV Protons

The energy dependence of the integral recoil properties and formation cross sections of a number of barium and strontium nuclides produced in the interaction of ${\mathrm{U}}^{238}$ with protons has been studied between 0.45 and 11.5 GeV. The ranges and forward-to-backward ratios ($\frac{F}{B}$) of the neutron-excessive products are nearly independent of energy, and the results indicate that these products are formed in binary fission following interactions with low deposition energies. The ranges of the neutron-deficient products are practically constant up to 1 GeV, decrease by nearly a factor of 2 between 1 and 5 GeV, and decrease very slightly thereafter. The $\frac{F}{B}$ values exhibit a pronounced peak in the vicinity of the midpoint of this interval. The results up to 1 GeV are consistent with binary fission. At this energy a different mechanism becomes noticeable and by 5 GeV this process predominates. Comparisons are made with the results expected for spallation, fission of a moderately light nucleus, and fragmentation. The latter is the only process which can account for the various experimental results. It is concluded that fragmentation is the main mechanism for the formation of neutron-deficient products lying in the "fission" region for incident energies above 5 GeV.