Monte-Carlo Simulation on Moderation of Positrons in Rare-Gas Solids

A Monte-Carlo code is newly developed and is used for studying the moderation of positrons in rare-gas solids. The mechanisms included are the interactions with excitons and phonons as well as the elastic and inelastic collisions. The analyses give the cross sections for the rare-gas solids of Ne, Ar and Xe. The simulation results give the implantation profiles for positrons incident onto the rare-gas solid and the energy dependence of the average depth. The fraction of positrons emerging from the incident surface is ∼40% even without any contribution from the implanted positrons. The exciton effect plays a predominant role in determining the behavior of the positrons in the rare gases, resulting in a decreased implantation depth and large backscattering fraction. A brief comparison between the simulation results and available experimental ones is performed.