Use of liquid scintillation counting for fast determination of 89Sr and 90Sr in milk

This paper describes a method of reproducibly recovering strontium (Sr) in 90.4% yield from 2-litre samples of raw milk in an analysis time of 5–8 h. All species which may interfere with the measurement of 89Sr and 90Sr are effectively removed; decontamination factors for Ca, Y, Ba and Cs were found to be adequate, and the role of other possible interferences is discussed. The Sr isolate was dissolved in scintillation cocktail prior to counting of 89Sr and 90Sr in a single measurement with a low-level liquid scintillation spectrometer. Scintillation spectra and counting efficiencies for 89Sr, 90Sr and 90Y have been established. A simple spectral stripping technique may thus be applied to calculate activities from the spectra of real samples. Results of analyses of five 2-1 milk samples containing known activities of 89Sr and 90Sr were respectively 87.7 ± 3.5% and 90.4 ± 3.0% (± 1 S.D.) of the activities added. A correction factor for the Sr yield was not applied. The detection limit of 0.014 Bq for 90Sr samples free of 89Sr implies that the method is also useful for routine monitoring of 90Sr.