Measurements of Strontium-90 in portuguese milk samples using liquid scintillation counting technique

The objective of this study is the implementation of a method combining extraction chromatography and liquid scintillation counting (LSC) technique to the determination of 90Sr in milk samples. The strontium separation is performed using the commercially available Sr-resin (Eichrom) and the beta counting is carried out using a liquid scintillation detector system (Tri-Carb 3170 TR/SL, Packard). Firstly, the trials are performed with 300 mL of milk and 0.7 g of resin. Validation trials are carried out using spiked milk samples with different 90Sr activities and the accuracy of the methodology is also been tested with an IAEA 152 reference milk sample. The results obtained had shown good accuracy of expected value. The minimum detectable activity (MDA) obtained for a confidence level of 95% and 60 minutes of sample counting time was 0.20 Bq L-1. In order to improve the detection limits for 90Sr, 1 liter of milk and 3 g of resin were used and the MDA value in these conditions was improved to 0.012 Bq L-1. The method was applied to the determination of the 90Sr concentrations in milk samples from different regions of Portugal