Use of Gamma-ray Spectrometry for Uranium Isotopic Analysis in Environmental Samples

Uranium is a rare earth element found in the earth’s crust with an average of 3 ppm. Natural uranium is a mixture of three radioactive isotopes U (99.27% abundance), U (0.72% abundance) and U (0.0054% abundance). It has been employed over the last seven decades as a source of energy and weapon. Enrichment processes were widely practiced to produce the necessary fuel. On the other hand, depleted uranium (DU) was also produced as a by-product of this enrichment processes. It was successfully used in many fields e.g. for shielding gamma radiation, penetrating calibers and as ballasts in aircrafts. Accordingly, monitoring of the isotopic U/U ratio could be a good indicative of the origin and/or activities associated with any uranium containing samples. Gamma-ray spectrometry is a powerful non-destructive analytical tool to determine the gamma emitters both qualitatively and quantitatively. Hyper-pure germanium detectors (HpGe) are widely used for gamma spectrometry measurements. They are favored over other detectors due to their distinctive resolving power. However, some photo-peaks from different radionuclides could still overlap together because of the proximity in their energy values so that the difference between them is less than the resolving power. An explicit example of that is the interference between the 185.7 keV photopeak of the U and the 186.1 keV photopeak of the Ra with branching ratios (f-value) of 57.2 % and of 3.5% for U and Ra respectively [1]. This problem could be easily handled if the radionuclide of interest