Quasi-elastic reaction cross sections and the merging instability

Considering a broad diversity of experimental heavy-ion data we suggest a physical separation between quasi-elastic (QE) and deep-elastic (DI) processes. Methods for the determination of QE cross sections are described, and 48 values are compiled. The separation is proposed to be related to an instability, and a formula for the prediction of QE cross section is derived. The formula is applicable to reactions with nuclei as light as nitrogen and as heavy as uranium at impact energies just sufficient to pass the interaction barrier up to three times the barrier. The ratio of experimental to model calculated data gives a weighted average of 0.99+-0.03 with a weighted mean deviation of +-17%. (orig.)