An Accurate Determination of the Cadmium Ratio of Neutron Capture Rates in ²³⁸U in Slightly Enriched Uranium

An experimental method of determining the ratio of the epicadmium ²³⁸U neutron-capture rate to the subcadmium ²³⁸U capture rate in a fuel rod, (ρ²⁸), is presented. The precision is ∼0.3% on the cadmium ratio. The relative ²³⁹Np and fission-product activities induced in a representative cross section of the fuel material (a thin bare foil of natural uranium) are compared with those induced in a cadmium-covered identical foil in a “flux symmetric” position in the rod. The ²³⁹Np gamma activity is counted by a coincidence method with and without the application of chemical separation. The results from the coincidence method are compared with two single-channel and one hundred-channel analyzer results obtained by chemical separation.