A new method for determination of uranium isotopes in water, vegetation and soil by alpha spectrometry

A new and accurate method for determination of uranium isotopes ( 238 U, 234 U and 235 U) in environmental samples by alpha spectrometry has been developed. Uranium is preconcentrat ed from filtered water samples by coprecipitati on with iron (III) hydroxide at pH 9-10 using ammonia solution and the precipitate is dissolved with HN0 3 and mineralised with H 2 02 and HF; uranium in biological samples is ashed at 600 °C, leached out with Na 2 C0 3 solution and mineralised with HN0 3, HF and H 2 0 2; uranium in soil samples is melted with Na 2 C0 3 and Na 2 02 at 600 °C and leached out with HC1, HN0 3 and HF. The mineralised or leaching solution in 2 M HN0 3 is passed through a Microthene-TOPO (tri- octyl-phosphine oxide) column; after washing uranium is directly eluted into a cell with ammonium oxalate solution, electrodeposited on a stainless steel disk and measured by alpha spectrometry. The lower limits of detection of the method are 0.37 Bq kg"1 (soil) and 0.22 mBq l"1 (water) for 238 U and 234 U and 0.038 Bq kg"1 (soil) and 0.022 mBq l"1 (water) for 235 U if 0.5 g of soil and 1 litre of water are analysed. Five reference materials supplied by IAEA have been analysed and reliable results are obtained. The average uranium yields for waters, mosses, lichens and sediments are 74.5+9.0%, 80.5±8.3%, 77.8±4.9% and 89.4±9.7% respectively.