Improvement of Multigroup Neutron L-order Truncated Negative Scattering Angular Distribution

The scattering angular distribution of the multigroup neutron transport equation, which is simulated by MonteCarlo method or discrete ordinate method, is usually expanded by Legendre series. Due to the Lorder truncated approximation, especial for L not enough large, the approximate angular distribution is negative over the range interval and nonunity by area. It leads to the nonphysics solution. In the paper, a generalized Gaussian quadrature discrete angle group is obtained by means of the equivalence of moment and Legendre coefficient. They are used as nodes of equally probable step function to approach real angular distribution, and then the nonphysics solution is avoided. The calculation results are the same as experiments and results of MCNP MonteCarlo code with continuous crosssection.