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Cs保持に関わる環境試料の前処理・分析手法の確立; ToF-SIMSを用いたCs同位体比測定の検討

Development of pretreatment and analysis for environmental samples containing radiocaesium; Preliminary ToF-SIMS analysis of Cs isotope ratio in the microparticle

田籠 久也*; 川村 秀久*; 草野 佳一*; 土肥 輝美

Tagomori, Hisaya*; Kawamura, Hidehisa*; Kusano, Keiichi*; Dohi, Terumi

森林生態系のCs循環に影響する可能性のあるリターに着目し、Cs量が比較的高いとされるCs含有粒子(CsMPs)の割合や特性を評価するため、それらの前処理・分析手法を検討した。粒径1$$sim$$10$$mu$$m程度のCsMPについては、有機物分解と電子顕微鏡を組み合わせて数千$$sim$$数万の土壌粒子を含むリター中から短時間(3日/1粒子)で特定可能とした。Cs同位体情報を得るための二次イオン質量分析法(ToF-SIMS)を適用する上では、数$$mu$$mレベルの試料探索が課題であった。そこで、集束イオンビームでCsMPの周囲にGaの目印を施すことで、ToF-SIMSによるCsMPの探索を容易にした。また、同試料のCs同位体(133Cs, 134(Cs+Ba), 135Cs, 137(Cs+Ba))スペクトルおよび二次元マッピングから各Cs同位体の分布情報を取得し、電子顕微鏡およびToF-SIMSを用いた微小試料の決定から同位体比測定までの一連の分析手法を確立することができた。

To investigate their spatial distribution and physicochemical properties of the radiocaesium-bearing micro particles (CsMPs), an efficient methodology for determine and analysis them is required. Here we focused on CsMPs from litters as they may affect the radiocaesium cycling in forest ecosystem. In this study we developed a method to determine CsMPs (mostly 1-10 $$mu$$m sizes) from litters by combine digestion treatment and automatic particle analysis with FE-EPMA. In total it took up to 3 days for detecting one CsMP from huge amounts of mineral-like and metallic particles. In the ToF-SIMS analysis for Cs isotope ratios of CsMPs to understand their emission source as the next step, pretreatment for easily detecting micron-sized samples is needed. To solve this problem, FIB technique was used for Gallium marking formation around target sample. Preliminary Cs isotope ratios(133Cs, 134(Cs + Ba), 135Cs, 137(Cs + Ba)) and their distributions of CsMPs were determined by applying these approaches. We developed pretreatment for microscopy and ToF-SIMS analysis of CsMPs.

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