Positron scattering from helium

Abstract

We have used our relativistic optical potential method to calculate a complete set of cross sections for positron scattering from helium over the range from 0 to 1 keV. We present elastic, positronium formation, direct ionization, total ionization and grand total cross sections and compare these to measurements and other calculations. Besides the previous method for calculating positronium formation by lowering the threshold for ionization to coincide with that for positronium formation in its ground state, we have also presented results where this process is represented by including the sum obtained by successively lowering the ionization threshold to coincide with those for positronium formation in the first four excited n levels. Agreement with previous work is generally good.