2023 Fiscal Year Final Research Report
Attempt of ultra-high sensitivity detection for long half-life radioactive cesium-135 by accelerator mass spectrometry
| Project/Area Number |
21K18622
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| Research Category |
Grant-in-Aid for Challenging Research (Exploratory)
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| Allocation Type | Multi-year Fund |
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| Review Section |
Medium-sized Section 15:Particle-, nuclear-, astro-physics, and related fields
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| Research Institution | University of Tsukuba |
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Principal Investigator |
Sasa Kimikazu 筑波大学, 数理物質系, 准教授 (20312796)
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| Co-Investigator(Kenkyū-buntansha) |
坂口 綾 筑波大学, 数理物質系, 教授 (00526254)
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| Project Period (FY) |
2021-07-09 – 2024-03-31
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| Keywords | セシウム135 / 加速器質量分析 / スパッタ負イオン源 / ルビジウム / タンデム加速器 / 微量分析 / 長半減期放射性核種 |
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| Outline of Final Research Achievements |
In recent years, development of an ultrasensitive detection method for a long half-life radioactive cesium-135 (Cs-135: half-life: 2.3 million years) is required as one of the anthropogenic nuclides in the nuclear age. However, the Cs sputtering negative ion source limits the analysis of cesium isotopes in AMS techniques with a tandem accelerator. In this study, we have developed the modified sputtering negative ion source using rubidium (Rb), which is the same alkali metal element, instead of Cs for the 6 MV tandem accelerator at the University of Tsukuba. 133Cs19F2- beam of 0.2μA was obtained from the cathode sample of Cs2SO4 mixed with PbF2 sputtered with Rb. CsF2- was accelerated at the terminal voltage of 6 MV, and passed through an Ar gas stripper. Cs9+ (58.7 MeV) and isobars were analyzed by the rare particle detection line to detect particles with a mass number of 135 in a gas ionization chamber.
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| Free Research Field |
加速器質量分析
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| Academic Significance and Societal Importance of the Research Achievements |
近年、核時代の人為起源核種の一つとしてセシウム135 (Cs-135:半減期230万年)の高感度測定法の開発が求められている。環境中に拡散された人工放射性核種は，生物・環境影響の観点からそのモニタリングは必須である。セシウム137（Cs-137:半減期約30年）は核分裂収率も大きく，これまでに多くの研究がおこなわれてきた。しかし，核実験起源のCs-137は，自然環境中では極微量となりつつある。Cs-135は，この代替トレーサーとして機能すると考えられている。本研究でのCs-135の高感度測定法の開発結果は，環境影響評価だけではなく，地球環境問題を扱う上で非常に重要な研究成果になると期待される。
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