Cherenkov counting of 90Sr and 90Y in bark and leaf samples collected around Fukushima Daiichi Nuclear Power Plant

The radioactivity of Sr-90 and Cs-137 in environmental samples, bark and leaf, collected around the Fukushima Daiichi Nuclear Power Plant in May 2013 was determined with the aim of investigating the migration of both nuclides using their radioactivity ratio. The radioactivity of Sr-90 was determined by using Cherenkov counting of Y-90 after purification using Sr resin and that of Cs-137 was determined by gamma-spectrometry. Quench correction in Cherenkov counting was investigated by measurements of samples spiked with purified Y-90 revealed that the radioactivity could be evaluated without quench correction. The radioactivity ratio of Sr-90 to Cs-137 in bark samples of 4.2 x 10(-3) and 1.2 x 10(-2) was compared with the results from soil samples collected in July 2011 to show that the migration of Sr-90 was slower than Cs-137 in bark and tree.