(U-Th)/He法のための高温加圧酸分解によるジルコンの完全溶解の試み

An Experiment of complete dissolution of zircon crystals by high-temperature and pressure acid digestion for the (U-Th)/He method

福田 将眞   ; 鏡味 沙耶   

Fukuda, Shoma; Kagami, Saya

本研究では、ジルコンのU-Th濃度の定量法として、東濃地科学センターにおいて初めて高温加圧酸分解による湿式分析を試みた。初めにジルコンを900Cで48時間アニーリングさせて、放射線損傷を回復させ、29Mのフッ酸に浸漬させて220Cで70時間加熱して溶液化させた。完全に分解されたことを確認するため、ICP-MS(Agilent 7700x)で検量線法を用いてZr濃度を測定した。結果として、理論値に近いZr濃度が得られたことから今回の条件下で完全に分解されたと考えられる。今後はブランクレベルの低減のため、クリーンブースでの作業や分析器具・条件の選定などについて再検討し、ジルコン(U-Th)/He法におけるU-Th濃度定量の技術整備を目指す。

In this study, we firstly attempted the wet-chemical analyses at Tono Geoscience Center based on a high-temperature and pressure acid digestion for determination of U-Th contents in zircon crystals. In the beginning, zircon crystals were annealed at 900 degrees Celsius for 48 hours to recover radiation damages, and annealed zircons were transferred and sunk into 29 M HF, and finally zircons were digested at 220 degrees Celsius for 70 hours. To verify that zircons were digested completely, Zr contents in zircons were measured as major elements by using ICP-MS (Agilent 7700x) based on the calibration curve method. As a result, theoretical values for Zr contents were obtained, these experimental conditions are thus valid for zircon digestion. Now, we are considering to perform these analyses in the clean booth and to select more appropriate analyses instruments and conditions for decreasing a blank level, which contributes to improve the determination of U-Th contents for zircon (U-Th)/He dating.