Comparative studies on ionizations in Ps-atom scattering using the Coulomb-Born approximation

Three different types of ionization in Ps-He scattering are studied using the Coulomb-Born approximation. Two different approaches are used to orthogonalize the continuum Coulomb wavefunctions. The non unitarity problem discussed by McAlinden et al (McAlinden M T MacDonald F G R S and Walters H R J 1996 Can J Phys 74 434) in Ps-atom scattering has been overcome in the present analytical methodology. All the important elastic and inelastic channels for both the atoms are taken into consideration. Comparison of the ionization cross sections with other atomic targets reveals the importance of van der Waals forces through the shifting of peak positions in agreement with the predicted strengths (Martin D W and Fraser P A 1980 J Phys B At Mol Phys 13 3383). The possibility of an additional channel is suggested from a comparison of the total cross section curve with experiment.