Positron Scattering from Gas-Phase Beryllium and Magnesium: Theory, Recommended Cross Sections, and Transport Simulations

Abstract

Results from the application of our optical potential and relativistic optical potential models to positron scattering from gas-phase beryllium (Be) and magnesium (Mg) are presented. Specifically, total cross sections and integral cross sections for the elastic, positronium formation, summed discrete electronic-state excitation, and ionization scattering processes are reported for both species and over an extended incident positron energy range. Where possible, these results are compared against the existing theoretical and experimental data, although it must be noted here that no current measurements are yet available for Be and those that are available for Mg are largely restricted to the total cross section. Nonetheless, on the basis of that comparison, recommended cross section datasets, for all the aforementioned cross sections, are formed. Those recommended cross section data are subsequently employed in a Boltzmann equation analysis to simulate the transport of positrons, under the influence of an applied (external) electric field, through the background Be and Mg gases. Note that relativistic optical potential results for the elastic momentum transfer cross section are also reported, to allow us to account for anisotropy effects in our transport simulations. Finally, our positron simulation results for quantities such as the ionization rate coefficients and flux and bulk drift velocities are compared with the corresponding electron transport results with significant differences being observed.