Modification of the LSC method for determination of uranium in water

Abstract

Uranium is a lithophile, reflecting its tendency to remain close to the earth's surface and be strongly bound to oxygen.A standard method ISO 13169:2018(E) “Water quality — Uranium — Test method using alpha liquid scintillation counting” is usually used for the determination of activity concentration of uranium in water samples by liquid scintillation counting. This paper presents the results of the modified application of the mentioned standard method and calibration results of LS counter Quantulus 1220, PerkinElmer. The applicability of the method was tested by using three different “two-phase” (water immiscible) scintillation cocktails produced by PerkinElmer: Ultima Gold F, Mineral Oil and Opti Fluor – O. For calibration purposes we used a natural uranium liquid calibration source, certified by Czech Metrology Institute, Prague. The innovation in the presented approach is that this calibration source was used as both alpha and beta emitter. As a first step in the calibration of the detector the discriminator factor, PSA was adjusted for each of the used scintillation cocktails. This step ensures the appropriate separation of alpha counts from beta counts in the obtained spectra.The obtained efficiencies for each of the scintillation cocktails are: for Ultima Gold F 75.6 (10)%, for Opti Fluor O 68 (9)% and for Mineral Oil 86 (6)%. The minimal detectable activities for the measuring time of 600 min are: for Ultima Gold F around 1 Bq/l, for Opti Fluor O 1.5 Bq/l and for Mineral Oil 1.3 Bq/l. In order to test the developed methodology samples of known activities were prepared with standard reference material and measured with all three scintillation cocktails. In addition to that, two samples of natural water from a former uranium mine were tested and gamma spectrometry results of the surrounding soil samples are also presented.