Data for Modeling of Positron Collisions and Transport in Gases

We review the current status of positron cross sections for collisions with atoms and molecules from the viewpoint of their use in studies of positron transport processes in gases, liquids and human tissue. The data include cross sections for positron scattering in rare gases, molecular gases (eg., for N-2, H-2, CO2, CF4) and in particular for organic molecules and those relevant for applications in medicine (e. g. formic acid and water vapor). The cross sections were taken from an assessment of previously published positron-target cross sections. All of the cross sections are based on binary collision measurements and theoretical calculations, and they were not explicitly modified according to the standard swarm analysis. The main reason for this is systematic lack of experimental data for positron transport properties in gases. However, we believe that our compiled sets of cross sections are at level of sophistication, and of sufficient accuracy, to provide correct interpretation of future positron-based experiments. Using these cross sections as an input in our Monte Carlo simulations and Boltzmann equation treatment, we review some interesting points observed in the profiles of various transport coefficients for positrons in gases. Particular emphasis is placed upon the analysis of kinetic phenomena generated by the explicit influence of Ps formation.