Abstract
The forward form of the Boltzmann equation is employed to obtain a new closed form expression for the path length distribution function of particles emitted from a plane source in an infinite medium. The power law cross section is used and the equations are solved by the use of Mellin transforms. We can obtain the spatial moments of the distribution function and, for certain restrictive conditions, study the influence of electronic stopping upon them. An asymptotic analysis is developed which enables the large-depth behaviour deduced earlier by Winterbon to be recovered and extended.