Dependence of neutron distribution calculation error on the order of PL approximation for the diffusion indicatrix

Regularities in calculation error formation when solving the problems of radiation transport with the presentation of augular dependences of multigroup scattering matrices in the form of a finite series by the Legendre polynomials are investigated. Conditions for superposition of errors conditioned by an approximated description of angular dependences for transitions matrix and distribution function are considered. The OPUS-PM program realizing IBL method is used for the caculations. The investigations are performed for three most wide-spread protective materials including water, iron and lead. Group density of neutron fluxes, space distribution of their basic functionals (dose equivalent, densiti of neutron fluxes with E>1.4 MeV and E>0.1 MeV) as well as angular distributions of these characteristics are investigated. A conclusion is drawn that the error of calculations performed without regard for group transitions, nicreases with the neutron energy decrease. In this case approximately equal values for simular neutron penetration depth are preserved. The presence of transitions from the upper groups reduces the errors