Neutron Fluxes in Concrete Ducts Arising from Incident Thermal Neutrons: Calculation and Experiment

Monte Carlo calculations, employing the albedo concept, have been carried out to determine the thermal-neutron flux distributions along the centerlines of a straight, a two-legged, and a three-legged square open concrete duct for a particularly demanding source geometry. The neutrons entering the duct were of thermal energy. The calculations used differential angular albedo data for concrete which have been reported previously. A comparison of the results of the calculations with those from a geometrically similar experiment shows good agreement and places on a firm foundation the concept of treating the thermal-neutron duct transmission problem as a reflection phenomenon at a point that is describable by the differential albedo properties of the walls.