Elastic scattering of electrons and positrons by atomic hydrogen and helium at intermediate and high energies

The eikonal Born series (EBS) method is used to analyse the elastic scattering of fast electrons and positrons by atomic hydrogen and helium. The properties of the terms of the Born and Glauber series are discussed, and in particular the dependence of these terms as a function of the (large) incident wavenumber k and the magnitude Delta of the momentum transfer. A more precise EBS treatment of small-angle scattering is presented by improving the calculation of the second Born term in this angular region. The EBS results agree very well with the recent absolute measurements of elastic differential cross sections, both for electron-atomic-hydrogen and electron-helium collisions.