Analytical Sciences

Simple Radiometric Determination of Strontium-90 in Seawater Using Measurement of Yttrium-90 Decay Time Following Iron-Barium Co-precipitation

Mitsuyuki KONNO*,** and Yoshitaka TAKAGAI*,***

*Faculty of Symbiotic Systems Science, Cluster of Science and Technology, Fukushima University, 1 Kanayagawa, Fukushima 960-1296, Japan
**Environmental Radiation Monitoring Centre, Fukushima Prefecture, 45-169 Sukakeba, Kaibama, Haramachi, Minamisoma, Fukushima 975-0036, Japan
***Institute of Environmental Radioactivity, Fukushima University, 1 Kanayagawa, Fukushima 960-1296, Japan

A radiometric quantitative methodology of ⁹⁰Sr in seawater was developed using a measurement of the ⁹⁰Y decay time following iron-barium co-precipitation. With calculations of its decay time, the radioactivity of ⁹⁰Sr can be indirectly determined under conditional environmental samples. In addition, to avoid the interference of other radionuclide, the prepared samples were measured using a germanium semi-conductivity detector; then, the deposited radioactivity was subtracted from the actual measurement values of beta-ray counting. In this paper, the seawater samples were collected within 2 km around Fukushima Daiichi Nuclear Power Plants during the term from October 2011 to March 2012. This method showed good linearity between the ⁹⁰Sr concentration and the total beta counting following the proposed method, with a correlation coefficient of 0.99 in seawater sample analysis. No interference that was caused by other radionuclides, such as radioactive cesium, was not observed in the quantification of ⁹⁰Sr. The whole process requires 12 h to quantify ⁹⁰Sr; this time is 1/40 shorter than traditional milking-low background gas-flow counting method. The lower limit of detection (average value n = 60) of the ⁹⁰Sr radioactivity was shown to be 0.03 Bq/L (uncertainty 4.2%).

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