  The alpha-radiometric determination of uranium after its pre-concentration
from natural water samples using the cation-exchange resin Chelex-100, 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 was determined to be
(97 +- 2) % for the cation-exchange, (95 +- 2) % for the liquid-liquid
extraction, and more than 99% for the electrodeposition. Employing
high-resolution alpha-spectroscopy, the measured activity of the U-238 and
U-234 radioisotopes was found to be of similar magnitude; i.e. ~7 mBq/L and ~35
mBq/L for ground- and seawater samples, respectively. The energy resolution
(FWHM) of the alpha-peaks was 22 keV, while the Minimum Detectable Activity
(MDA) was estimated to be 1 mBq/L (at the 95% confidence limit).
