Neutron emission inC12+Gd158andC13+Gd157reactions between 8 and 12 MeV/nucleon

Neutron spectra in coincidence with evaporation residues and with projectilelike fragments emitted in inelastic scattering reactions have been measured at several bombarding energies for ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$- and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$-induced reactions leading to the same compound nucleus ${}_{}{}^{170}{}_{}{}^{}\mathrm{Yb}$. In the fusion reactions, a nonequilibrium component was observed in the neutron spectra at all beam energies. This component is forward peaked and is associated with a high temperature. The spectra can be parametrized by assuming the nonequilibrium part to result from a hot region ($T\sim 4$ MeV) emitting neutrons isotropically and moving with a velocity of approximately 1 cm/ns. This apparent velocity decreases with decreasing beam velocity. Comparisons are made with predictions based on the generalized critical angular momentum model of incomplete fusion of Siwek-Wilczynska et al. No significant difference has been observed between nonequilibrium neutron emission from ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$- and ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$-induced reactions. Neutron emission associated with inelastic scattering reactions cannot be described by simple statistical evaporation from two fragments of equal temperature. Effects which may give rise to the observed energy and angular distributions of neutrons in coincidence with inelastic products are discussed.