Polarization Effects in the Elastic Scattering of Electrons from Helium

The cross section for elastic scattering of electrons from helium atoms has been computed for an energy range from 0 to 50 eV. The formalism used here was obtained from an extension of Hartree-Fock theory wherein the distortion induced in the atom by the scattering electron is approximated by a polarization potential. The method is similar to the "adiabatic-exchange" treatment of electron-hydrogen scattering by Temkin and Lamkin. The computed scattering phase shifts and cross sections are compared with various other calculations and experimental data. A scattering length of $1.13 a_0$ is extrapolated from the phase shifts after correcting them for the effects of truncating the polarization interaction as required in the iteration process. The computed total cross sections compare favorably at low energies with the data of Ramsauer and Kollath and at very low energies with the modified effective-range theory of O'Malley, Spruch, and Rosenberg. The differential scattering cross sections follow the effective-range theory in a high backward asymmetry at low energies and the experimental data in a high forward asymmetry at higher energies. The momentum-transfer cross sections agree well with recent microwave drift-velocity measurements, especially those of Pack, Phelps, and Frost.