Development of Cs separation methods from large amounts of soil samples to determine the 135Cs/137Cs isotope ratio

Since the ¹³⁵Cs and ¹³⁷Cs concentration level of environmental soil in prefectures adjacent to Fukushima is low at about 5.5 × 10⁻¹⁵ − 6 × 10⁻¹³ g g⁻¹, a large amount of soil is required to obtain sufficient amount to measure them precisely. Two Cs separation methods which allow to treat large amounts of leached soil solution were developed: 1) A continuous butch extraction method using calix[4]arene-bis(t-octylbenzo-crown-6) and 2) A combination method of selective Cs adsorption using ammonium phosphotangstate and anion-cation exchange resins. These methods were applied to low Cs concentration samples, and good precision of 0.8–2.1% in the measurement of ¹³⁵Cs/¹³⁷Cs isotope ratio was obtained.