2018 年 34 巻 11 号 p. 1277-1283
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%).