Positron-Electron Differences in Energy Loss and Multiple Scattering

Abstract

The Bhabha cross section for positron-electron scattering is used to derive the average rate of collision loss by positrons passing through matter, which differs from the corresponding expression for negative electrons by a few percent. The spin and exchange terms of the Bhabha and M\o{}ller cross sections produce small corrections also in the Landau distribution of energy losses by positive and negative electrons in thin foils, the most probable energy loss being less affected than the shape of the distribution. Positron-electron differences in the average cosine of the multiple-scattering angle, and in the penetration depth at which the particles have lost their memory of initial direction, are calculated from the appropriate elastic cross sections; the difference in rate of energy loss is included in the calculation. Numerical examples for Al and Pb are given.