The Angular Distribution of Particles Emerging from a Diffusive Region and its Implications for the Fleck-Canfield- Random Walk Algorithm for Implicit Monte Carlo Radiation Transport

We present various approximations for the angular distribution of particles emerging from an optically thick, purely isotropically scattering region into a vacuum. Our motivation is to use such a distribution for the Fleck-Canfield random walk method [l] for implicit Monte Carlo (IMC) [2] ra la ion transport problems. We demonstrate d’ t that the cosine distribution recommended in the original random walk paper [l] is a poor approximation to the angular distribution predicted by transport theory. Then we examine other approximations that more closely match the transport angular distribution.