[M-IS14] 水惑星学

[MIS14-06] はやぶさ2帰還試料のマルチ同位体分析技術の開発

*横山 哲也¹、Gautam Ikshu¹、大熊 悠介¹、飯塚 毅²、はやぶさ2初期分析チーム 「同位体・元素分析班」 (1.東京工業大学理学院地球惑星科学系、2.東京大学理学系研究科地球惑星科学専攻)

キーワード：はやぶさ2、リュウグウ、初期分析、マルチ同位体測定

The sample-return mission Hayabusa2 conducted two sampling sequences that collected the surface and sub-surface materials from a C-type asteroid, Ryugu in 2019. The Sample Return Capsule (SRC) containing the collected materials was brought back to the Earth on Dec 6th of 2020. The curation team opened the SRC in a clean chamber at the curation facility of JAXA at Sagamihara, and found black chunks of rocks and dust from Ryugu, of which the total weight reached >5 g. Although the retrieved sample mass was far more than that was expected at the planning stage (0.1–1 g), each of the initial analysis team can use only limited amount of the samples (< 0.1 g) to obtain scientific data that characterize the asteroidal materials. We have developed a technique for a multi-isotopic analysis that uses ~ 30 mg of the Ryugu sample. Two terrestrial basalts (BCR-2, BHVO-2) and two CM chondrites (Murchison, Jbilet Winselwan) were chosen as the analog samples to evaluate the performance of the developed technique. The powdered sample was decomposed by a mixture of HF + HNO₃ in a Teflon vessel. The sample was conditioned with HBr for the separation of Pb by anion exchange chromatography (Column-1; AG1-X8). The major element fraction of the Column-1 was dried and conditioned with 0.4 M HCl-0.5 M HF for the separation of Ti+Zr+Hf, W, and Mo (Column-2; AG1-X8). The major element fraction of the Column-2 was dried and conditioned with 6 M HCl for the separation of Fe and U (Column-3; AG1-X8), followed by the separation of Sr and Ba (Column-4; Sr-Resin), REEs (Column-5; RE-Resin), Ca (Column-6; DGA-n Resin), and Cr (Column-7; 1:1 mixture of AG50W-X8 and AG50W-X12). Finally, Mg and Ni were separated using Ni Resin (Column-8). The recovery yields of individual target elements are generally >90% during each step of the chromatography. However, these loss are not unique to our method and is always associated during any chemical separation procedures. Although extreme care was taken for handling samples but a certain loss are unavoidable such as during sample drying, pipetting and sample sticking to the Teflon beaker. The isotopic compositions of these analog samples, especially for Cr and Ti, will be reported in the presentation.