Year
1993
Abstract
High-enriched uranium(HEU) emits sufficient thermal power and gamma rays that a combination of calorimetric assay and gamma-ray spectroscopy can be used for the determination of 235U content. The thermal power is primarily generated by the 234U fraction that is enriched along with the 235U diinrig isotopic separation processes. HEU with an enrichment of 93% 235U contains about 1% 234U and the resultant specific power is 2 milliwatts/kilogram. This is sufficient power for assay by high sensitivity calorimeters of quantities of HEU metal, high-grade scrap, feed and process materials. The calorimetric measurements are used in conjunction with measurements by high-resolution germanium detectors of the relative gamma-ray intensities of 234U and 235U. The 234U/235U ratio is determined using the 121 keV 234U and 144 keV 235y gamma rays. The measured intensities of 235U gamma rays(144 - 200 keV) are used to estimate the relative efficiency of detection for the two gamma peaks. The isotopic ratio is calculated using the measurement data and the known 234U and 235U branching ratios and half-lifes. The 235U content of a container can be determined from the 234U/235U isotopic ratio and the quantity of 234U as determined by calorimetry. The calorimetric/gamma-ray technique requires no physical standards and could be used for verification measurements or for the characterization of physical standards. The results of measurements performed on HEU samples will be reported. This work is supported by the US Department of Energy, Office of Safeguards and Security under Contract #DE-AC04- 88DP43495