Next event estimation of cell tallies

In Monte Carlo particle transport studies, one is often interested in the estimation of the average particle flux in a given volume. The average particle flux in a volume and the volume-integrated particle flux are examples for what is called cell tallies in this paper. Estimation of cell tallies by using the track length estimator is a well-established technique. Next event estimation is well known from the estimation of point fluxes. What is presented here is the generalization of the principle of next event estimation onto the estimation of cell tallies. For the practical realization, I give three different estimation schemes with increasing degree of sophistication are given. Application to a simple model problem reveals that for an important class of problems, next event estimation is much more efficient than the track length estimation.