Momentum Space Coupled Channels Optical Method For Positron-rubidium Scattering

In recent years, more and more attention has been concentrated on positron scattered by atoms. Great success have been achieved both experimentally and theoretically, a number of theoretical calculations have given successful predictions that cover almost all aspects of the positron-hydrogen system. However, as to the many-electron atoms scattering with positron, there remain obvious discrepancies between the experimental measurements and the theoretical predictions, for the various reaction within the complex collision system. Nowadays, with the remarkably improvement on the experimental technology, corresponding descriptions from the theory are expected urgently, which comes into being the great challenge to our theoretical workers.It is very significant to investigate the scattering of positrons by alkali atoms detailedly. In the past 20 years, some theoretical models have been developed to the positron-alkali atoms collision, wherein the common models include the distorted-wave Born approximation method(DWBA), the R-matrix method, the convergent close coupling method(CCC), the coupled-channels optical potential method(CCO), developed in 1980's by McCarthy et al, has been widely applied to the electron scattered by various atoms and molecules and has achieved great success.In this paper, we propose a complex, local polarization to represent the positronium formation(Ps) arrangement channel and the ionization continuum channel, and develop the CCO method to the positron collision with the complex atom, rubidium. We calculate the Ps(n=1,2) cross sections, elastic cross sections, 5s-5p excitation cross sections and the total cross sections for positron scattering by Rb at intermediate energies. The present total cross sections are in good agreement with the measurements of Parikh et al. and other theoretical calculation results. This conclusion shows that the CCO method is an available method to investigate the scattering for positron with complex atoms. But from the comparison of our CCO results with the experimental data and other theoretical calculation results, we can find some shortages of our CCO theory. In our calculations, we don't consider the action of the incident positron with the electrons lies in the inner orbits of rubidium. Further more, in this paper, we can not calculate the ionization cross sections which are significant in the positron-atom at low energies. Therefore, there must be some error in our results with the reality. The following work in our research is how to reduce the error.In the end, we hope that our results can impulse the development of theoretical and experimental work about the scattering of positron with rubidium. The further experimental and theoretical data for positron-Rb collision are expected.