Path-length dependent flux from random walk theory

Calculation of the flux Ψ(R, s) due to a point isotropic source in an infinite medium, as a function of the distance R and actual pathlength s is treated as a random walk problem. In the case of isotropic scattering, this method is shown to lead to a standard transport-theoretical result, for the integrated flux. However, for Ψ(R, s) far from the source, the random walk theory predicts a modified maxwellian form.