A new method for the determination of low-level actinium-227 in geological samples
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We developed a new method for the determination of 227Ac in geological samples. The method uses extraction chromatographic techniques and alpha-spectrometry and is applicable for a range of natural matrices. Here we report on the procedure and results of the analysis of water (fresh and seawater) and rock samples. Water samples were acidified and rock samples underwent total dissolution via acid leaching. A DGA (N,N,N′,N′-tetra-n-octyldiglycolamide) extraction chromatographic column was used for the separation of actinium. The actinium fraction was prepared for alpha spectrometric measurement via cerium fluoride micro-precipitation. Recoveries of actinium in water samples were 80 ± 8 % (number of analyses n = 14) and in rock samples 70 ± 12 % (n = 30). The minimum detectable activities (MDA) were 0.017–0.5 Bq kg−1 for both matrices. Rock sample 227Ac activities ranged from 0.17 to 8.3 Bq kg−1 and water sample activities ranged from below MDA values to 14 Bq kg−1of 227Ac. From the analysis of several standard rock and water samples with the method we found very good agreement between our results and certified values.
KeywordsActinium-227 Extraction chromatography Water Rock Alpha-spectrometry
We would like to acknowledge Phil Horwitz and William Burnett for their advice on the extraction chromatographic techniques. Ken Sims’ lab at the Woods Hole Oceanographic Institution performed the rock dissolution procedures and Ken Buesseler (WHOI) provided the counting equipment for the alpha-spec analysis. Jan Scholten from the IAEA provided the actinium standard and spiked seawater samples.
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