An improved electron energy-loss straggling algorithm for Monte Carlo transport codes.

Abstract

The commonly used Blunck and Leisegang electron energy-loss distribution falls off too rapidly with increasing energy loss. Also, for large thicknesses and/or low-Z media, where their distribution should approach Landau's, it normalizes to 0.92 rather than 1.0, it overestimates the number of very small energy-loss events, and its peak is shifted from lambda = -0.225 to 0.1. Because of these shortcomings, calculations made using this distribution yield a mean straggled energy loss which is lower than the value predicted by the continuous slowing down approximation (CSDA). An improved version of the Blunck-Leisegang distribution, which exhibits better normalization and falloff, has been developed. Further, an algorithm was created which (depending on the CSDA energy loss, Z,A, electron energy, and transport step size) samples the electron's straggled energy loss from the more accurate of the available distribution functions.