Challenges to measuring ultra-trace anthropogenic U-233 in the environment

2021 Fiscal Year Final Research Report

• Project/Area Number: 18K19849
• Research Category: Grant-in-Aid for Challenging Research (Exploratory)
• Allocation Type: Multi-year Fund
• Review Section: Medium-sized Section 63:Environmental analyses and evaluation and related fields
• Research Institution: University of Tsukuba
• Principal Investigator: SAKAGUCHI Aya 筑波大学, 数理物質系, 准教授 (00526254)
• Co-Investigator(Kenkyū-buntansha): 山崎 信哉 筑波大学, 数理物質系, 助教 (70610301)
• Project Period (FY): 2018-04-01 – 2022-03-31
• Keywords: ウラン同位体 / 加速器質量分析 / 物質循環 / 人工放射性核種

Outline of Final Research Achievements

Although U-233 was expected to have been released into the environment as a result of human nuclear activities, its measurement has been difficult because the amount/concentrations of this nuclide in the environmental samples are tremendously small. In this study, efforts have been made to establish a method for analysing U-233 together with other uranium isotopes in the environment as simply as possible, by investigating chemical separation methods for environmental samples and improving the sensitivity of accelerator mass spectrometry. As a result, U-233 and other uranium isotopes were successfully measured in samples of a few grams in corals and oceanic sediments and a few litres in surface seawater. This has made it possible for the first time to determine when and how much U-233 was supplied to the Earth's surface environment. The results have been presented at conferences and in journal papers and are expected to be applied in many fields.

Free Research Field

環境放射化学

Academic Significance and Societal Importance of the Research Achievements

環境中の人工放射性ウランは、放射線防護や放射能による環境影響評価において重要なだけではなく、その物理化学的性質から環境動態を明らかにするツールとして有用である。そのため、本研究により環境中の極微量U-233の測定が実現したことは、物理や化学の基礎科学的な分野から動植物含めた環境評価や地球科学分野への応用、また今後ますます重要となる核鑑識や保証措置技術への貢献など様々な分野への波及効果は大きい。特に環境中には極微量のウラン同位体U-236も存在していることから、これらU同位体の濃度とともに、U-233/U-236比を利用することによる応用研究のポテンシャルは計り知れない。