Simplified model for positronium-helium scattering

Abstract

Using a local effective potential to account for electron exchange, the authors have analysed the zero-energy scattering of ortho-positronium by helium atoms. The effective potential was chosen so that the results obtained in the static approximation agreed with the static-exchange results of Fraser and Kraidy (1966). Correlation was introduced in two different approximations which agree well. A decrease is found in the scattering length a from 1.72 a0 to 1.39 a0, and an increase of more than a factor of 2 in the quenching rate of the positronium (from Zeff=0.042 to 0.10), as compared with the static-exchange approximation. This gives improved agreement with the experimental value Zeff approximately=0.18.