Monte Carlo calculations have been performed for source energies from 1 to 10 Mev, and normally incident radiation, showing that 90% of the infinite-barrier energy flux albedo is reached with a 10 cm concrete wall. The spectrum of backscattered energy flux is presented for the above sources and wall thicknesses ranging from 5 to 50 cm. An analytical expression, based on a single-scattering approximation, is shown to produce good fits to the Monte Carlo results.