The Barkas effect - or Z13, Z14-corrections to stopping of swift charged particles

The Barkas effect is the difference in stopping of swift, positive and negative particles. This qualitative discussion of it concerns the theory of higher Z1-corrections to the Bethe formula. It is shown that simple classical concepts suffice for obtaining main features of stopping formulae. Thereby, a simple conception of the Z13-correction is achieved, the magnitude being about twice that in previous work. In comparisons between α-particles and protons one must in addition apply the Z14-correction of Bloch. (Auth.)