Recent progress of Cs concentration and Cs/Cs isotopic ratio measurement

Shimada, Asako 

Cesium-135 is one of the important nuclides to assess the safe disposal of High Level Waste (HLW). Therefore, the calculation code and library to evaluate the Cs concentration in HLW have been improved through comparisons with experimental results. On the other hand, even basic data of Cs, such as its half-life, have large uncertainty. Because the Cs/Cs isotopic ratio suggests its origin and introduction date, the ratios in environmental samples are measured to study global fallout from nuclear weapons testing and nuclear accidents. Such measurement methods was attracted attention, in particular, after the accident at the Fukushima Daiichi Nuclear Power Station. Measurement of the Cs/Cs isotopic ratio in environmental samples was challenging because the radiocesium has a very low concentration and it co-exists with huge amounts of Ba isotopes, which are isobaric interfering nuclides, are co-exist. Chemical separation methods were developed to eliminate interfering nuclides and improve the performance of the mass spectrometer to enable the measurement of the ratios. In this review, the features of the Cs/Cs isotopic ratio for each origin and recent developments in measurement techniques are summarized.