The Fine Adjustment of the Neutron Penetration in the NRN Method

Recommended values have been experimentally obtained for the angle (defined by its cosine µ₀ in center-of-mass system) that determines the boundary between ‘removal’ and ‘nonremoval’ collisions and regulates the deep penetration of neutrons in the NRN method. Measured attenuations in three different, most common, shield materials: water and magnetite and ordinary concrete, give µ₀ = 0.6 (± 0.1) for elements with A > 1. For hydrogen, µ₀ = 0.45 is recommended. The results indicate, besides, that the neutron flux predictions are not overly sensitive to the changes in the removal source, caused by varying µ₀. The usual smoothing effect of the diffusion is material dependent, and the strength of the coupling between removal and diffusion parts is seen to decrease when going from water to magnetite and ordinary concrete.