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レーザー共鳴イオン化法によるストロンチウム同位体分析法の開発,2

Development of resonance ionization mass spectrometry of Sr isotopes, 2

宮部 昌文; 大場 正規; 赤岡 克昭; 若井田 育夫; 長谷川 秀一*

Miyabe, Masabumi; Oba, Masaki; Akaoka, Katsuaki; Wakaida, Ikuo; Hasegawa, Shuichi*

福島第一原子力発電所事故に関わる放射能計測では、純$$beta$$崩壊核種で、$$^{90}$$Zrなどによる同重体干渉も生じる$$^{90}$$Srの計測(放射化学的分析法, ICP質量分析法)に、熟練と時間のかかる化学分離操作が求められることが大きな問題となっている。本研究では、元素や同位体の原子構造の違いを利用して、特定同位体のみを高効率でイオン化できる多段階共鳴イオン化法と、イオンを長時間捕捉・計測可能なレーザートラップ分光法を組み合わせることで、迅速かつ高感度な$$^{90}$$Sr分析法の開発を目指している。本報告では、探索した電離効率, 同位体選択性の高い3段階電離スキームを用いて、同位体毎のSr原子の電離特性や分析特性について検討した。

Because of environmental pollution of the radioactive materials released from TEPCO's Fukushima Daiichi Nuclear Power Station, considerable attention has been focused on food safety in Japan. Whereas the principal pollutants for foods are radioactive $$^{135}$$Cs and $$^{137}$$Cs, the radioactive $$^{90}$$Sr, one of the alkaline earth elements like Ca and its radiation can damage bone marrow, is also one of the most important nuclide considering the possible occurrence of biological concentration through food chain. This $$^{90}$$Sr is the pure $$beta$$-ray emitter of which energy is 0.546 MeV (28.78 years) and is known as the nuclide for which analysis is difficult. For radiometric analysis, to eliminate various $$beta$$ emitters which potentially interfere the $$^{90}$$Sr analysis, not only a repeated application of ion-exchange and coagulating sedimentation processes but also a period of longer than 2 weeks are needed to establish radioactive equilibrium between $$^{90}$$Sr and its daughter nuclide $$^{90}$$Y. To realize a prompt $$^{90}$$Sr analysis for marine foods, we are developing a new analytical technique by combining resonance ionization spectroscopy (RIS) and ion trap detection. In the present study, we have evaluated ionization efficiency and analytical performances using highly efficient and isotope-selective RIS scheme which we determined in our previous study.

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