New aspects of enhanced ion scattering near 1800

A new approach to the 1800 backscattering phenomenon has been taken by looking at it as a flux peaking effect. A simple model calculation based on the flux peaking point of view shows considerable agreement with experimental results. Because flux peaking in the present circumstances suggests the existence of more than one possible path in reaching a target atom, plots were made of the inward and outward portions of any ion trajectory that emerged from the target within a very small angle (0.0250) of the exact backward direction. In these plots we have observed there to be a sizeable contribution to the effect by interchangeable return paths that exist. As a consequence, the usual explanation of the phenomenon as reversibility back along the original ingoing path accounts for only part of the enhancement in a typical case. Also, it appears that all trajectories returning very near 1800 are transformed in nature from those that occur at angles well away from the backward direction. Our results demonstrating the existence of interchangeable return paths provide part of the explanation of why the two-atom model predicts too small an effect. Another part of the explanation appears to lie in the fact that multiple small-angle collisions with target atoms provide even more focusing or path tolerance than a collision with just a single target atom. The present work has been on random solids but the same mechanism should also act in scattering from either the bulk or the first few atomic layers of a crystalline solid