Angular anisotropy of group averaged absorption coefficient and its effect on the behavior of diffusion approach in radiative transfer

Multi-group method, a generally accepted procedure for handling the radiative transfer equation, is accompanied by the group averaged absorption coefficient, and actually the coefficient is angularly anisotropic. In the paper, we present a brief discussion how the anisotropy of the coefficient makes the material absorb photons at different rate in each direction, also study its effect on the diffusion approach by comparing the results calculated using multi-group diffusion and multi-group discrete ordinate SN for the isotropic and anisotropic group averaged absorption coefficients respectively, and find that the anisotropy deteriorates the behavior of diffusion approach.