Some aspects of the relation between the energy dependence of the scattering cross section and the spatial distribution of neutrons slowing down in a hydrogeneous moderator are discussed. The neutron population in an infinite medium is analyzed using the mean square slowing down distance, , as a measure of its spatial extent. It is shown that, contrary to what is perhaps expected, the neutron population in many cases is distributed closer to its source with decreasing energy. In the analysis of this behavior it is found that diffusion theory may in some cases be expected to give good results close to the spatial position of the source. A correction term is also found for the “first flight” transport kernel often used in practical calculations.