Algorithm for forcing scattered radiation to arbitrary convex regions in neutral particle Monte Carlo simulation

A new algorithm is presented to improve the efficiency of neutral particle Monte Carlo radiation transport. When a radiation quantum is produced from a source or undergoes a scattering event, it is divided into two parts. One continues to undergo the normal analogue transport process. The other is deterministically transported to a randomly selected point on the surface of an arbitrary convex region, from where it continues normal transport. Application of this approach substantially improves efficiency in cases where particles must reach small geometric regions in order to make tally contributions. The algorithm is demonstrated in a simulation of X-ray scattering in a radiographic imaging application.