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Zr-93の質量分析を目的としたZr-91濃縮安定同位体標準液の調製

Preparation of Zr-91 stable isotope standard solution for determination of Zr-93 by mass spectrometry

今田 未来; 浅井 志保; 半澤 有希子; 間柄 正明

Konda, Miki; Asai, Shiho; Hanzawa, Yukiko; Magara, Masaaki

ICP-MSを用いた同位体希釈質量分析法(IDMS)により、使用済燃料や高レベル放射性廃棄物中に存在する長寿命核種Zr-93を定量するためのスパイクとする標準液を、Zr-91濃縮安定同位体標準(以下、Zr-91標準)を金属の状態で入手し溶解して調製することとした。Zr-91標準を溶解する前に、模擬金属Zr試料を用いて溶解条件を検討した。最適な条件であった3v/v% HF-1 M HNO$$_3$$混合溶媒0.2mLによってZr-91標準2mgを溶解し、1M HNO$$_3$$を用いて希釈して濃度を約1000$$mu$$g/gとした。市販のZr元素標準液をスパイクとして、ICP-MSを用いたIDMSによりZr-91標準溶解液の濃度を(9.6$$pm$$1.0)$$times$$10$$^2$$$$mu$$g/gと決定した。定量結果が予測したZr濃度と一致したことから、Zr-91標準溶解液は化学的に安定な状態で存在していること、及びZr-91標準溶解液中の不純物測定結果から不純物の有意な混入がないことを確認した。これらの結果から、調製したZr-91標準溶解液は、Zr-93分析用の濃縮安定同位体標準液として十分な品質を有していることが示された。

Isotope dilution mass spectrometry (IDMS) with ICP-MS is reliable method for determination of Zr-93, which is one of the long-lived fission products found in spent nuclear fuel and high-level radioactive wastes. In order to use an isotope standard solution of zirconium as the spike for IDMS, dissolving a commercially available solid isotope standard is indispensable. Prior to the dissolution of the Zr-91 isotope standard, solubility of metal zirconium in a mixture of HNO$$_3$$ and HF was evaluated using zirconium metal chips. Then, 2 mg of the Zr-91 isotope standard was dissolved with 0.2 mL of 1 M HNO$$_3$$-3 v/v% HF mixed solution, followed by adjusting the concentration of Zr-91 to approximately 1,000 $$mu$$g/g. IDMS, in which a natural isotopic abundance standard solution of zirconium was used as the spike, was employed for the determination of the concentration of Zr-91 in the prepared Zr-91 isotope standard solution. The concentration of Zr-91 in the prepared Zr-91 isotope standard solution was (9.6$$pm$$1.0) $$times$$ 10$$^2$$ $$mu$$g/g, which is in good agreement with the predicted concentration. This indicates that the Zr-91 metal isotope standard was completely dissolved with sufficient chemical stability. Additionally, no impurities were detected in the prepared Zr-91 isotope standard solution. These positive results denote that the Zr-91 isotope standard solution with the preferable quality for IDMS of Zr-93 can be obtained by the proposed dissolution procedures.

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