Recoil properties of radionuclides formed in the interaction of 1-300-GeV protons with gold

The thick-target recoil properties of a number of nuclides, varying from ${}_{}{}^{22}{}_{}{}^{}\mathrm{Na}$ to ${}_{}{}^{196}{}_{}{}^{}\mathrm{Au}$, formed in the interaction of 1-300-GeV protons with ${}_{}{}^{197}{}_{}{}^{}\mathrm{Au}$ have been measured in order to study the systematics of their variation with product mass and incident energy. The forward-to-backward ratios ($\frac{F}{B}$) of many of the products have a peak at 3 GeV and decrease at higher energies, with products in the mass region $46\le A\le 65$ having $\frac{F}{B}=1.0\mathrm{}$ at 300 GeV. The $\frac{F}{B}$ values of products with $A\gtrsim 140$ decrease monotonically between 1 and 300 GeV. The results are analyzed by the two-step model of high-energy reactions and discussed in terms of the different reaction mechanisms, spallation, fission and fragmentation. Fission contributes appreciably to the formation of products in the mass region $46\le A\le 103$ at 1 GeV bombarding energy, but other mechanisms predominate at and above 11.5 GeV. The results are compared to the predictions of intranuclear cascade-evaporation calculations, and are in reasonable agreement at 1 and 3 GeV, although the calculations predict more forward momentum transfer than is observed. At higher energies the relation between forward momentum and mean deposition energy derived from the calculations must break down, because nuclides requiring high deposition energies for their formation have little or no forward momentum. Some possible explanations for this phenomenon are discussed.