Computing Absolute Thermal Neutron Flux from Measurements Made with Indium Foils

The method for computing absolute thermal neutron flux from measurements made with activated indium foils is described. By combining data from the counting rate of indium foils in 2π proportional counters with appropriate corrections for foil weights and neutron effects, the thermal flux is expressed in terms of σ_O, the thermal absorption cross section of In¹¹⁵. This procedure may be used by laboratories which do not have access to a standard graphite pile or to a standard neutron source. This method has an estimated error of less than 5% which is a function of the accuracy with which it is possible to determine the various correction factors for beta counting. A possible fixed error in the value of σ_O can easily be corrected for and incorporated into the methods used.