Vectorized algorithms for Monte Carlo simulation of kilovolt electron and photon transport.

Abstract

This work investigates the transport of electrons having energies near those of the atomic binding levels of the elements (roughly the 1 to 100 kilovolt range) using the Monte Carlo modeling technique. The work has been divided into three phases. In the first phase, basic physics models of individual electron collision processes have been systematically compared with relevant experiments and the most accurate and most readily adaptable to high speed computing have been identified. Short summaries of the approximations employed in the derivation of microscopic cross sections have been presented in an attempt to provide analytically derived validity conditions for comparison with those determined through experimental comparison. In the second stage, cumulative scattering descriptions, which model the cumulative effect over a finite pathlength of the many individual collisions on the behavior of electrons, are examined. A study of derived and experimentally determined validity conditions for the cumulative scattering descriptions has been performed. In the final phase of the project, the condensed history (which uses primarily the cumulative scattering distributions), the single scattering (which uses the microscopic cross sections), and the single elastic scattering (which uses a combination of microscopic and cumulative effect distributions) Monte Carlo algorithms for modeling the transport of electrons have been examined. The limitations of each with respect to initial electron energy, media atomic number and applicability to specific problems have been identified using computer programs constructed from several of the optimal basic physics models. A model-independent, fully vectorized algorithm has been devised for each of the three main transport schemes. In addition to permitting previously infeasible (due to run time restrictions) single scattering simulations, the formalism employed has allowed simple and convenient interchange of differential cross section and cumulative scattering data for the reported accuracy optimization studies.