@misc{oai:repo.qst.go.jp:00072660,
 author = {S.K.Sahoo and N.Kavasi and T.Aono and サフー サラタ クマール and Ｋａｖａｓｉ Ｎｏｒｂｅｒｔ and 青野 辰雄},
 month = {Sep},
 note = {In the nuclear accident of the Fukushima Daiichi Nuclear Power Plant (FDNPP), a pure β particle emitter fission product 90Sr was emitted along with gamma emitter nuclides, such as 137Cs, 134Cs, 131I and 132Te. 137Cs and 90Sr have long-lasting radioecological impact due to longer half-life (>30 y). Furthermore, the 90Sr has a long biological half-life (˜18 y) in the human body. Due to its chemical similarity to calcium it accumulates in bones and irradiates the bone marrow, causing its high radio-toxicity. Therefore, assessment of 90Sr in the environment is necessary from the viewpoint of a nuclear disaster.
\nFor 90Sr measurement, a new separation laboratory was established at the National Institutes for Quantum and Radiological Science and Technology, Japan (QST) in 2012. Analyzing Fukushima soil samples collected in 2013, we have noticed a weak correlation between 90Sr and 137Cs activity concentrations, however, the 90Sr concentration was lower with three or four magnitudes than 137Cs (Sahoo et al., 2016, Kavasi et al., 2015). In this study, a soil sample collection survey in the Fukushima exclusion zone was accomplished in 2016 and some contaminated hot spots were revealed with air dose rate measurement (>20 µSv/h). 137Cs activity concentrations were over 1000 kBq kg 1 while the 90Sr were over 500 Bq kg 1.
\nWe are developing a method to measure 90Sr using thermal ionization mass spectrometry (TIMS) since it is the technique of choice due to 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. By the use of special lense like WARP filter for TIMS, an upper limit of 1.0 x 10-10 was achieved. 
\nThis work was supported partially by a research grant from Fukushima Prefecture related to Research and Development in Radiological Sciences., 4th International Conference on Radioecology and Environmental Radioactivity 2017},
 title = {Elevated 90Sr activity concentration in Fukushima soil samples},
 year = {2017}
}