報告書番号

N09028

タイトル（和文）

地下水年代測定評価技術の開発（その11)－36Cl/Cl分析の高精度化を目的とした新しい前処理手法の確立－

タイトル（英文）

Research and development on groundwater dating (Part11)-The proposal of separation method of chloride and sulfate ion for accurate measurement of 36Cl/Cl-

概要 （図表や脚注は「報告書全文」に掲載しております）

塩素の放射性同位体である36Clは、30～180万年程度の地下水年代を評価するための重要な指標である。36Cl正確な評価のために、サンプルの塩化物イオンと硫酸イオンを分離する前処理が必要とされる。本研究では、既往手法における欠点を克服可能な、新しい塩化物イオンと硫酸イオン分離法として、カラムクロマトグラフィーを基にした「カラム法」に着目し、36Cl測定の前処理法としての可能性を検討した。種々の試験を通じて、カラム法において塩化物イオンと硫酸イオンを分離可能な条件を決定し、塩化物イオンと硫酸イオンの分離法として確立した。カラム法は硫酸バリウム法に比べて(1)分離精度が高い、(2)オペレータの技量への依存度が低い、(3)希薄溶液にも対応可能、（4）6時間程度で処理を終了することが可能、といった長所があることを示した。

概要 （英文）

36Cl is one of the most powerful tools to estimate the residence time of groundwater about 300-1800 thousand years. AMS(Accelerator Mass Spectroscopy) can provide accurate estimation of 36Cl. However, estimation of 36Cl by AMS is usually disturbed by isobar such as 36S. Thus, separation of Cl (usually Cl- form in groundwater) and S (usually SO4-2 form in groundwater) is required for accurate estimation of 36Cl. In previous studies, a methodology (BaSO4 Method) that uses the difference in solubility between BaSO4 and BaCl2, had been applied as pretreatment method for 36Cl estimation by AMS. However BaSO4 Method has following disadvantages; (1) Cl and SO4 can not be separated completely, (2) accuracy of separation depends on the skills of operator, (3) it takes a long time for treatment, (4) it can not be applied to dilute solutions. Therefore, new methodology that can overcome disadvantages of BaSO4 method is required for more accurate estimation of 36Cl.
In this study, Column Method based on column chromatography was investigated for pretreatment method for 36Cl estimation by AMS to separate Cl and SO4 ions. The conditions for Column Method were determined and adjusted so that Cl and SO4 ions were separated completely and sufficient amount of Cl for 36Cl estimation can be treated. The results of AMS measurement showed Column Method can remove SO4 from Cl more effectively comparing with BaSO4 method. Furthermore, Column Method was found to have following advantages over BaSO4 Method; (1) dependence of accuracy of separation on the skills of operator is quite low, (2) treatment can be done within 6 h, (3) it can be applied to dilute solutions.

報告者

キーワード