Positron Impact Ionization of Hydrogen, Sodium, and Potassium

The total ionization cross sections for positron scattering by hydrogen, sodium, and potassium are calculated by applying an equivalent-local optical potential model from the ionization threshold to 300eV. The total ionization cross sections are in excellent agreement with the recent measurements of Jones et al. The total ionization cross sections for sodium and potassium are compared with other theoretical calculations.