A modified statistical analysis is proposed to account for the enhanced back angle scattering for certain heavy ion collisions. The fluctuation differential cross section, influenced by barrier top resonances, is predicted to approach a ${\left|P_{l_0}\right(\theta \left)\right|}^2$ form, where $l_0$ is the orbiting angular momentum. A statistical expression for the magnitude of the 180° fluctuation cross section is derived and applied to the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ elastic scattering at 30 MeV (c.m.). Numerical estimates, based on parameters in the literature, are found in qualitative agreement with observation.

[NUCLEAR REACTIONS Back angle enhancement in heavy ion elastic scattering. Modified statistical treatment. Estimates for ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ + ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, 180° cross sections at $E_{\mathrm{c}.\mathrm{m}.\mathrm{}}=30\mathrm{}$ MeV. Barrier top resonances.]

• Received 3 November 1980

DOI:https://doi.org/10.1103/PhysRevC.24.125