Z3corrections to the scattering of electrons and positrons in atoms and to the energy loss of fast particles in solids

Abstract

A calculation of the elastic scattering cross section for the screened Coulomb potential of a charge Ze provides second-order terms, of relativistic and nonrelativistic origin, that are proportional to Z/sup 3/. Here we study the Z/sup 3/ effects in the elastic scattering of electrons and positrons in atoms and in the energy loss of fast charged particles in solids, for a wide range of energies. Owing to the Z/sup 3/ effect, the scattering of electrons in atoms becomes always larger than the scattering of positrons. In the relativistic limit this agrees with the result of McKinley and Feshbach for bare nuclei. The screening effect introduces a nonrelativistic enhancement of the Z/sup 3/ correction; this increases the asymmetry between electron and positron scattering. Using the same approach we calculate the contribution from close collisions to the Z/sup 3/ correction in the energy loss of fast particles in solids. For nonrelativistic velocities the Z/sup 3/ correction shows a behavior similar to the result of Ashley, Ritchie, and Brandt, including distant and close collisions; in the relativistic limit we retrieve the result of Jackson and McCarthy. The limitations of this approach in describing distant collisions, and the validity of the partition rule, aremore » considered.« less