Cross Section and Recoil Properties of Copper Isotopes from Uranium Bombarded with 11.5-GeV Protons

Cross sections and thick-target recoil properties have been measured for ${}_{}{}^{61}{}_{}{}^{}\mathrm{Cu}$, ${}_{}{}^{64}{}_{}{}^{}\mathrm{Cu}$, and ${}_{}{}^{67}{}_{}{}^{}\mathrm{Cu}$ from the interaction of ${}_{}{}^{238}{}_{}{}^{}\mathrm{U}$ with 11.5-GeV protons. The kinetic energies are much smaller than expected from a conventional fission process, even for the neutron-rich ${}_{}{}^{67}{}_{}{}^{}\mathrm{Cu}$. It is proposed that these Cu nuclides are produced at proton energies above 3 GeV by the fission of low mass nuclei which are the residues of an intranuclear cascade process involving high deposition energy and the emission of fragments prior to fission both in the fast cascade and the evaporation stage.