Anisotropic Angle Biasing of Photons

A synergistic method is described for the angle biasing of anisotropic scattering kernels in Monte Carlo calculations. The method generalizes Dwivedi's suggestion of using the exponential transform to cancel the undesirable fluctuations of angle biasing. Only photons are examined because the biasing of the Klein-Nishina scattering kernel can be treated analytically in contrast to more general neutron scattering kernels, which would require a numerical treatment. Three-dimensional continuous-energy results indicate that angle biasing in conjunction with the exponential transform is better than either by itself and greatly enhances Monte Carlo transport for the cases shown.