THE HALF-ON-SHELL COULOMB T-MATRIX IN MULTIPLE-SCATTERING APPROXIMATIONS TO ATOMIC IONIZATION PROCESSES

In the light of new absolute measurements of triple-differential cross sections for electron-impact ionization of helium we re-examine the v arious forms of the Coulomb T-matrix in the plane-wave impulse approxi mation. At higher energies the regularized form is supported by the me asurements of Pochat et al while the Ford form is supported by the old er, conflicting, measurements of van Wingerden et al. A revised calcul ation of the second-order Faddeev-Watson approximation is presented an d compared with the measurements of Pochat et al.