Determination of Uranium Concentration and Attenuation Correction in Dense Highly Enriched Uranium (HEU) Material by the Comparison of Gamma Rays from Tl-208

摘要

This report describes a method for determining the uranium concentration of dense Highly Enriched Uranium (HEU) material. The method uses gamma rays from Tl-208 to determine a mass-attenuation coefficient, each of which produces an activity for Tl-208. Typically gamma rays from U-235 would be used, but because of the high density of the material the low energy gamma rays are unreliable. The higher energy Tl-208 gamma rays are used instead. The Tl-208 is a daughter of U-232 which is an extremely small component of highly enriched weapons grade uranium. The U-232 is homogenously distributed with the other isotopes of uranium. Therefore the Tl-208 gamma rays travel through identical material as the gamma rays form these other isotopes of uranium. Although U-232 comprises less than a part per billion of the uranium mass, it produces extremely useful gamma rays. This method can be applied using the Interactive Analysis Plot screen in ISOTOPIC Operator.