For the photon transport kernel in form of the Thomson scattering function and a restrictive photon diffusion directed only toward free surface, several exact expressions of back scattered fluxes are demonstrated. The solving approach was established on a lemma proved by Placzek combined with the Fourier analytic inversion technique or the order of scattering method. Albedo problem in case of the homogeneous plane shield of iron subjected to the photons normally incident on the free surface is treated. Comparison of the results obtained by the analytical and Monte Carlo methods for the reflection of 40 and 60 keV photons from iron target confirms the domination of the single scattered photon flux and the strong influence of the scattering function anisotropy in reflection process at low energies.