Positron-helium scattering including polarization effects

Abstract
An integral form of the polarized-orbital method has been employed to investigate the positron-helium collision problem. This form does not satisfy the minimum principle. A change of sign of the s-wave phaseshift occurs in the low-energy region. The zero position is obtained at an energy slightly higher than that given by variational calculations. The total elastic cross-section values below the Ps formation threshold are in qualitative agreement with experimental results as well as with the more refined theoretical findings. The Ps formation cross section for the partial wave l=1 shows a resonance-like behaviour near 20 eV. A similar feature has also been noticed by Kraidy and Fraser (1967) around 23 eV.

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