[M-AG33] Basic study on the estimation of the "Black Rain" area caused by the atomic bomb

[MAG33-P03] Development of Isotope Ratio Analysis and Microarea Imaging Method for Radioactive Materials

*Masato Morita¹, Shouki Yoshimura¹, Tetsuo Sakamoto¹ (1.Kogakuin University)

Keywords:Isotope analysis, Microimaging, Laser resonance ionization, Radioactive materials

The need for isotope analysis is increasing in fields such as the Fukushima Daiichi Nuclear Power Plant, nuclear weapons testing, and planetary science fields such as meteorite dating. Analytical methods such as ICP-MS and TIMS can determine isotope ratios with high precision. However, they cannot obtain local information in solids, because they are bulk analyses. On the other hand, EPMA and TEM-EDX can observe local elemental distributions in solids with high surface resolution, but cannot analyze each isotope. Secondary ion mass spectrometry (SIMS) is a method for mass spectrometry of secondary ions generated by ion beam sputtering. Although it is possible to analyze isotopes locally in a solid, SIMS has the problem of isobaric interference because the ionization mechanism lacks element selectivity. Laser resonance ionization sputtering neutral mass spectrometry (R-SNMS) that we have developed uses two wavelength tunable lasers to pass through an excited level to neutral atoms generated by ion beam sputtering. As a result, only the target element is ionized, and each isotope can be analyzed by mass spectrometry.
The R-SNMS method consists of two main parts: a proprietary FIB-TOF-SIMS device and a grating-type Ti:Sa laser. FIB-TOF-SIMS instruments can simultaneously image all elements with extremely high surface resolution (up to 40 nm). In addition, FIB allows on-site cross-sectional processing and analysis of the interior of solids. The grating-type Ti:Sa laser has a high repetition rate of 10 kHz for synchronization with FIB-TOF-SIMS, and the grating angle can be adjusted automatically. This makes it possible to quickly and automatically switch to conditions in which only the desired isotope is ionized. In this presentation, we will introduce the features of the FIB-TOF-SIMS and R-SNMS instruments, along with examples of analysis of radioactive cesium etc. originating from Fukushima.