Cross Sections for the Production of ${\mathrm{Li}}^9$, ${\mathrm{C}}^{16}$, and ${\mathrm{N}}^{17}$ in Irradiations with GeV-Energy Protons

Twenty-five targets ranging from boron to uranium were irradiated with 1.0-and 2.8-GeV-energy protons. Cross sections for the production of the nuclides ${\mathrm{Li}}^9$, ${\mathrm{C}}^{16}$, and ${\mathrm{N}}^{17}$ were measured by counting the delayed neutrons which they emit. No longer lived delayed-neutron emitters were observed except those produced as fission products from uranium. Cross sections for the latter are presented and interpreted in terms of low-deposition-energy processes. Cross sections for the nuclides ${\mathrm{Li}}^9$, ${\mathrm{C}}^{16}$, and ${\mathrm{N}}^{17}$ from the lightest targets are interpreted as simple spallation products, mainly from ($p,xp$) reactions. Several pairs of targets with similar mass number and differing neutron-to-proton ratio were studied. A strong dependence of the cross sections on the neutron-to-proton ratio of the target was observed, especially for the lighter mass regions. Relative cross-section calculations were performed for the heavier targets assuming these and other light fragments were evaporated from excited knock-on cascade products. The effect of secondary evaporation from excited evaporated fragments was included. The experimental and calculated relative cross sections agree well with respect to their dependence on the mass number and neutron-to-proton ratios of the target. It is concluded that the mass-energy surface, which is included in the evaporation formalism, is important in determining the relative yields of light fragments.