Abstract
Uranium isotopes U-238, U-234, and U-235 are alpha-particle emitters and can be directly measured by alpha spectrometry. To evaluate the accuracy of the determination of low concentration of U isotopes in water samples, six spiked water samples were analysed by extraction chromatography using uranium selective resin. The separated uranium isotopes were electrodeplated on a disc of stainless steel and were measured by an alpha spectrometer for the determination of radiochemical yield using U-232 isotopic tracer. Three certified IAEA reference water samples (IAEA-Cu-2010-03, IAEA-420 and IAEA-421) have been analysed for method validation. The measurement uncertainty sources were identified, and the combined standard uncertainty of the measurement has been determined. Although the activity of uranium isotopes in the certified reference samples was very low, the obtained results were reliable and were within the certified range with 95% confidence level. The characteristic limits (the decision threshold and detection limit) were calculated. The combined uncertainty of the results was mostly attributed to the count rates in the region of interest of the analyte and the tracer in the blank as well as in the sample spectra. Based on the results of the acceptance criteria including Z-score, u-test, trueness and precision, the used radiochemical procedure was found accurate and precise as well.