Run of the number of visits of a pseudo particle in a cell (which is proportional to the mean intensity) with cell number (which is proportional to the optical depth starting at the left) in a slab that is illuminated from the left but does not have internal sources. The curves represent ratios of absorption to extinction ε = 0,10^-3,10^-2,10^-1 (from top to bottom). In all cases, N = 10⁵ pseudo particles are used.