Radiometric determination of uranium in natural waters after enrichment and separation by cation-exchange and liquid-liquid extraction

Preconcentration of uranium from natural water samples using Chelex-100 cation-exchange resin, its selective extraction by tributylphosphate and electrodeposition on stainless steel discs is reported. The validity of the separation procedure and the chemical recoveries were checked by addition of uranium standard solution as well as by tracing with U-232. The average uranium yield for the cation-exchange was (97 +/- 2)%, for the liquid-liquid extraction was (95 +/- 2)% and for the electrodeposition was more than 99%. Employing high-resolution alpha-spectroscopy, the measured activity of U-238 and U-234 radioisotopes was found to be similar to7 mBq.1(-1) and similar to35 mBq.1(-1) for ground- and seawater samples, respectively. The energy resolution (FWHM) of the alpha-peaks was 22 keV, the minimum detectable activity (MDA) was estimated to be 1 mBq.1(-1) (at 95% confidence limit).