Recent Progress of 135Cs Concentration and 135Cs/137Cs Isotopic Ratio Measurement

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-135 concentration in HLW have been improved through comparisons with experimental results. On the other hand, even basic data of Cs-135, such as its half-life, have large uncertainty. Because the Cs-135/Cs-137 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 attracted attention, in particular, after the accident at the Fukushima Daichi Nuclear Power Station. Measurement of the Cs-135/Cs-137 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. 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-135/Cs-137 isotopic ratio for each origin and recent developments in measurement techniques are summarized.

Automated summary

This article summarizes the characteristics of the Cs-135/Cs-137 isotopic ratio and the latest developments in measurement techniques. Cs-135 is one of the important nuclides to assess the safe disposal of High Level Waste (HLW), but its basic data, such as half-life, have large uncertainties. The measurement of the ratio in environmental samples can be used to study global fallout from nuclear weapons testing and nuclear accidents.