DETERMINATION OF DEPLETED URANIUM IN ENVIRONMENTAL SAMPLES BY GAMMA-SPECTROSCOPIC TECHNIQUES

The use of depleted uranium (DU) in military operations causes the contamination of the target area due to DU dispersion in the environment. Since the isotopic abundance of uranium in DU is different than that in nature, the only evidence of DU contamination is the disruption of the natural isotopic abundance of 238U and 235U. For the investigation of the existence of such a disruption, the accurate determination of 235U and 238U is necessary. The Nuclear Engineering Section of the National Technical University of Athens (NES-NTUA) uses high-resolution LEGe detectors and especially developed gamma spectroscopic analysis techniques for the determination of 238U, 235U and subsequently for the isotopic abundance of the uranium isotopes in the sample. Uranium 235 is determined from the analysis of the multiplet photopeak at 186 keV. DU may be detected with this technique provided that the 238U activity of the DU is higher than ~20% of that of 238U in the natural uranium of the sample. The analyses by NES-NTUA of surface soil samples collected well before the dispersion of depleted uranium in Kosovo, made evident that Kosovo is an area of high natural background, with a pronounced surface soil variation in natural uranium content, and 238U activity reaching values as high as 330 Bq kg-1. It was also observed that disturbance of radioactive equilibrium among the nuclides of the uranium series is quite often observed due to leaching and weathering, with the ratio of the activities of 238U and 226Ra ranging from 0.17 to 5.5. After the military operations in Kosovo, surface soil and vegetation samples as well as DU penetrators were analysed in NES-NTUA. Among the soil samples analysed it was found that some of those collected around a DU penetrator crater were contaminated by DU, with 238U activity exceeding 2 kBqkg-1, and ratio of 238U/226Ra exceeding the value of 10. In these soil samples, the natural isotopic abundance of the uranium isotopes was significantly disrupted; this allowed for an estimation of the isotopic abundance of 235U in the dispersed DU of about 0.2%, which agrees very well with relevant values found in the literature for DU penetrators. DU in the vegetation samples analysed was below detection limit. The analysis of DU penetrators led to the detection 238U, 235U and their daughters, and to an estimation of the dose-rate due to the gamma-rays emitted from the penetrator, which reached 6.5 μSvh-1 on the surface, sloping to background at the distance of about 40 cm.