Natural uranium isotopes determination in 24h-urine samples from exposed workers to enriched uranium

Individual monitoring of occupationally exposed workers to enriched uranium is mandatory, due to its radiotoxicity. The aim of this work is to determine if the use of Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and an estimation method for 234U activity, could supply the information obtained by Alpha Spectrometry (AS), which is the analytical technique commonly employed in this scenario. A total of 105 samples of 24 h-urine from exposed workers were analyzed by both techniques and the obtained results were compared. 235U activity results were only quantifiable in 7 samples by AS (0.07–0.30 mBq/d) while ICP-MS quantified it in most of the cases.238U activity was measurable in 88 samples by AS and ICP-MS with wide range of results (0.11–2.4 mBq/d). For these isotopes no significant dosimetry differences were found between both techniques. However, 234U activities results obtained by AS ranged from 0.15 to 7.6 mBq/d and the isotopic ratio of 234U/238U were highly variable. 234U estimation was done with the average of these isotopic ratios and 235U and 238U ICP-MS results. Significant differences between estimated results and the ones obtained by AS were observed. Therefore, ICP-MS cannot supply the information given by AS, although can complement it. New studies must be started in order to obtain better and faster results applying radiochemical separation and ICP-MS measurement and studying the real contribution of diet in final uranium dose assessment.