Milk+Powder+and+Strontium

Back to Main Strontium is determined from milk powder. Milk powder is a good starting material because to it has been concentrated from large amount of milk. Organic matter is incinerated and ash dissolved into small amount nitric acid. Strontium is separated from alkali metal with phosphate precipitation. Removal of potassium is of special interest since it interferes with strontium separation with extraction chromatography by using SrResin (Eichrom/Triskem). From the eluate of SrResin strontium is precipitated as strontium carbonate for yield determination, dissolved in acid and measured with liquid scintillation counting.

90 Sr (t½ 28.8 a, Emax 0.54 MeV) decays with β-emission to the daughter nuclide 90 Y (t½ 64.0 h, Emax 2.28 MeV) which starts to grow in to a sample immediately after the separation of strontium. The β-spectra of 90 Sr and 90 Y are overlapping and therefore the ingrown 90 Y interferes with the measurement of 90 Sr activity. The 90 Sr-source has to be measured either immediately after the separation of strontium or when yttrium and strontium are in equilibrium in the sample in about two weeks. In equilibrium the activities of 90 Sr and 90 Y are the same. Complete achievement of equilibrium is not necessary since the ingrowth percentage can be calculated from the time difference between the separation and the measurement. In this exercise strontium is measured after the ingrown of 90 Y with a low background liquid scintillation counter (Quantulus, Wallac, Perkin Elmer). The counter is calibrated with a 90 Sr standard solution in which 90 Y is in equilibrium with 90 Sr.