Convoy electron production in heavy ion-solid collisions

Abstract

The properties of the sharp ν c ≌ ν cusps observed in the velocity spectrum of convoy electrons ( υ e) ejected in heavy ion-solid collisions in the ion velocity range (ν) 6–18 a.u. are compared to the properties of analogous cusps observed in binary electron capture to the continuum (ECC) and electron loss to the continuum (ELC) collisions in gases. Apart from a skew toward ν e > ν, the ν-independent convoy distributions observed are very similar to those for ELC and the cusp widths are the same in both cases. While the shape of convoy peaks is approximately independent of projectile Z, ν, and of target material, yields in polycrystalline targets (C, Al, Ag, Au) exhibit a strong dependence on Z and ν. Coincidence experiments in which convoy electrons are allocated according to emergent ion charge-state q e show a surprising independence of q e, mirroring the unweighted statistical emergent charge-state fraction Coincidence experiments on O 6+ ,7+ ,8+ ions traversing 〈 110 〉 and 〈 100 〉 channels in Au show a strong yield suppression and a dependence of yield on the channel chosen. Interpretation of these observations, comparisons to convoy production studies using protons, and a discussion of remaining puzzles is given. The history of ECC, ELC, and “wake-riding” models of convoy electron production is also reviewed.