A Novel Method for the Measurement of 90Sr Using Thermal Ionization Mass Spectrometer

There is a great demand for rapid measurement of Sr-90 in environmental samples after the Fukushima Dai-ichi nuclear power station (FDNPS) accident. 90Sr (t1/2 = 28.8 y) is one of the most common and hazardous fission products released by a nuclear reactor accident. Measurement of 90Sr using radiometric methods is a time consuming process since it involves a complex sample preparation and analytical separation required to produce reliable data. Thermal ionization mass spectrometry (TIMS) is the technique of choice because of its inherent high precision and accurate measurement of isotopic ratio. Typical abundance sensitivity for strontium isotope ratio measurement with conventional TIMS is about 10-7. The perfect chemical separation of radiocesium from Sr-90 is a cardinal point to gain accurate Sr-90 result as the radiocesium also undergoes beta decay emitting gamma-rays. A new 90Sr analysis method was developed using the Isotopx Ltd., Phoenix X62 TIMS. The abundance sensitivity for the 90Sr/88Sr ratio was 2.1×10 10 and this could ensure detection limit of 100 Bq·kg 1 (19 fg·g 1) 90Sr in Fukushima soil samples. The method has been validated using two certified reference materials e. g. wild berry (IRMM-426) and freshwater lake sediment (NIST-4354). This mass spectrometry method is faster than conventional radiometric techniques.福島大学環境放射能研究所第8回成果報告