An Absolute Thermal-Neutron-Flux Standard

A useful and inexpensive assembly for thermal-neutron-flux standardization is described. This assembly consists of a water filled tank containing three Pu-Be neutron sources, each located at an apex of an equilateral triangle with sides of 5.6 inches and appropriately centered in the tank. The thermal flux is spatially invariant and isotropic over a rather large region in the test section and thus reduces the effects of positioning errors of foils and detectors being calibrated. Methods for standardizing such an assembly are discussed.