COULOMB BORN APPROXIMATION FOR ELECTRON-SCATTERING FROM NEUTRAL ATOMS - APPLICATION TO ELECTRON-IMPACT IONIZATION OF HELIUM IN COPLANAR SYMMETRICAL GEOMETRY

A new perturbation series in which the electron-electron interaction is treated perturbatively is used to compute (e, 2e) cross sections for helium in coplanar symmetric geometry at energies of 100 and 200 eV. The perturbation theory is written such that the slow decrease of the Coulomb potential in which the incoming and scattered particles move becomes irrelevant, and so do the asymptotic conditions of the zero-order wavefunctions. We compute the triple differential cross section using Coulomb waves with an effective charge for the incoming, scattered and ejected electrons and find very good agreement with experiment and with previous calculations, especially in that there is a double peak in the cross section, with a deep dip at an angle close to 90-degrees.