Investigation of 6Li + 13C scattering and observation of a nuclear quasi-rainbow

Differential cross sections for elastic scattering of 6Li ions by 13C at Ec.m.s. = 26 MeV are measured in the range of c.m.s. angles 14 - 163 degrees at the Kurchatov Institute cyclotron in both direct and inverse kinematics by the ΔE-E telescope technique. A broad maximum in the angular distribution that is exhausted completely by the far component is observed at approximately 100 degrees. The maximum is a typical manifestation of the nuclear rainbow and can be explained by the interference of waves arriving from the two branches of the deflection function (DF). However, for the potential chosen in this study, the DF has a singularity, and nuclear-rainbow scattering cannot formally take place because there is no finite scattering angle. The observed effect, which is referred to as a quasi-rainbow, demonstrates that the principal peculiarities of elastic scattering are the same in the two energy regions that are considered in a direct semiclassical approximation as corresponding to two fundamentally different phenomena: orbiting and the rainbow. 11 refs., 4 figs., 1 tab