GM検出器を用いたY-90β線測定による水中のSr-90濃度の高感度・簡便測定法

Strontium - 90 / Y - 90 are major radionuclides observed in the water samples tested recently at the site of the Fukushima Daiichi Nuclear Power Station of Tokyo Electric Power Company. A simple method of evaluating Sr - 90 concentration in these water samples by measuring β rays from Y - 90 with a GM - detector setup was developed. By applying the precipitation method, Sr - 90 and Y - 90 were separated and quantitatively collected with a filter. β rays from Y - 90 in the filter were measured two times at appropriate intervals by inserting a polyethylene plate of 2 mm thickness as a β -ray absorber. The contribution of γ rays from Cs - 134 and Cs - 137 to the Y - 90 count rates was quantitatively evaluated using a 10-mm-thick acrylic resin plate. From the parent-daughter relationship between Sr - 90 and Y - 90, the Sr - 90 concentration was evaluated using the conversion coefficient of Y - 90 count rate （ cps ） to Sr - 90 concentration （ Bq / cm 3 ） . It was verified that Sr - 90 concentration of below 0.01 Bq / cm 3 in water samples can be correctly measured by this simple method.