The Momentum Transfer Cross Section for Electrons in Helium

Abstract

Measurements of the drift velocity, the ratio of diffusion coefficient to mobility, and the "magnetic drift velocity" for electrons in helium have been made at 293°K in the range 1.8 X 10⁻¹⁹ < E/N < 3 X 10⁻¹⁷ V cm². From an analysis of the drift velocity data, an energy-dependent momentum transfer cross section has been derived for which an error of less than ± 2 % is claimed over the central portion of the energy range. The cross section agrees with the theoretical cross section of La Bahn and Callaway to within 2% over the whole energy range. The agreement with the cross section derived by a number of procedures from the total elastic scattering cross section measured by Golden and Bandel is less satisfactory. The drift data are sufficiently accurate to enable a search to be made for the effects of fine structure in the cross section at low energy. The results do not support the existence of such structure.