Cross-sections and velocity distribution functions for elastically scattered positrons by alkali atoms

By using the previously reported approach, which combines in a simple way the polarized orbital method and the JWKB approximation, phase shifts, differential elastic and momentum-transfer cross-sections are calculated for positron-alkali atom collisions for the energy range E=0.54 to 6.66 eV. The differential cross- sections exhibit a deep minimum near theta=90sup(deg) at low energies, while the momentum-transfer cross-sections are fitted well by the law C/E, allowing the analytical determination of equilibrium positron distribution functions in a gas of alkali atoms in the presence of an electric field. Results on positron energy loss rates are also reported. Whenever possible, the situation encountered in the positron-alkali gas interaction is compared to the corresponding situation of the positron-noble-atom gas. The reported results, while being obtained as a rule by adopting very simple procedures, are hoped to be useful in stimulating more accurate and extensive work in this new and perspective field