Background: Due to the potential public health effects of releases of uranium to the environment, isotopic determination and measurement of this radionuclide in environmental samples is very important. Achieving this goal, monitoring programs for this radionuclide seems necessary to be applied in many countries.

Materials and Methods: The uranium was separated from the water samples using anion
exchange resin (Dowex 1×8 Cl^- form) and then purified by electrodeposition or co-precipitation method with Lanthanide fluorides such as Lanthanum fluoride (LaF₃) and finally the prepared source it is counted by Alpha spectrometry.

Results: The activity of ²³⁴U, ²³⁸U and natural uranium (U-nat) in 4 water samples, sent by
Analytical Quality Control Services (AQCS) center of International Atomic Energy Agency (IAEA), were determined and the results were compared with the AQCS laboratories data. The ranges of measured activities for low and high activity samples were from 3.217×10^-3 to 597 Bq/kg respectively.

Conclusion: Since the results were relatively close to the AQCS data, the applied procedure seems to be proper for isotopic uranium determination. It was observed that in case of low
activity level samples, preparing source by co-precipitation method showed more accurate
results. Iran . J. Radiat. Res., 2004 2 (1): 35-40