A Low-Order Approximation for Highly Anisotropic Multigroup Transport Cross Sections

It is shown that for transport problems involving fine-energy-group structure or light element scattering, the elastic scattering transfer cross sections can be approximated by trapezoid-shaped distributions. In particular, for group structures of equal lethargy widths, the trapezoidal distribution reduces to a triangular shape. These approximate transfer cross sections are readily incorporated into a discrete ordinates code and often produce results superior to those obtained with conventional Legendre expansion techniques.