The distribution of backscattered gamma ray photons in the scattering medium

Monte Carlo calculations were performed to simulate the behaviour of photons scattered back from a semi-infinite medium. The source considered was point isotropic on the surface of the medium, and the media simulated soils of various densities. The values of the number albedo obtained agreed well with those quoted in the literature. The radial distribution was found to fall off exponentially, with a dependence on distance from the source practically independent of source energy and material, provided the photo electric absorption cross section at the source energy is negligible. This conclusion is supported by calculation from results quoted in the literature. The distributions of the initial direction cosine relative to the radius joining source and point of exit, and of the number of scatters, were calculated and tabulated.