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Planta, 118020 Buirelonu, S p i n l h e validation of the Cerenkov radiation measurement of to determine the activity concentration of "Sr in environmental samples is described. Liquid-liquid extraction with di-2-ethyhexylphosphoric acid in toluene was used to separate 90Y from 90Sr. Optimum conditions for Cerenkov counting (low-level counting option, counting windows, mass of solution to be measured) were established. The need for a counting efficiency correction by using a colour quench curve is stated to be essential, otherwise a significant error may occur. Two different colour quench curves (counting efficiency versus the channel ratio or spectral index parameter) were used and the results were compared. The method was applied to 12 environmental matrices: sea-water, algae, carobs, milk, almonds, hake, honey, shellfish, lamb meat, sardine, pork meat and shore sand. No significant differences were observed on using either of the two colour quench curves for any of these environmental matrices. In order to validate the proposed method, a certified soil reference material (CRM IAEA-375) was used, together with participation in an interlaboratory exercise to determine 90Sr in a natural water sample. Again, efficiency correction was performed by using either of the two colour quench curves and in both instances the calculated 90Sr activity concentration was in good agreement with the known values.

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