Particle transport in inhomogeneous media

A method is described for simulating particle transport in a medium which is homogeneous on a macroscopic scale but contains small regions having a different composition from the bulk medium. Modelling the regions explicitly becomes prohibitively expensive when their number density is large. Instead, a sampling scheme is developed which randomly positions regions in the path of the particle being tracked and then discards them once the particle moves on. Two example applications of the method are described, namely modelling the transmission of beta-rays through pneumatically suspended finely ground coal and the gamma-ray energy deposition distribution in aerated water. In both cases, it is found that a detailed treatment of the inhomogeneous medium yields appreciably different results from assuming a uniform mean composition. (orig.)