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Preliminary test for $$^{129}$$I measurement of CaCO$$_{3}$$ samples in JAEA-AMS-TONO

JAEA-AMS-TONOにおける炭酸カルシウム試料のヨウ素129分析の予備試験

三ツ口 丈裕 ; 岡部 宣章*; 三宅 正恭*; 松原 章浩; 藤田 奈津子   ; 渡邊 隆広   ; 國分 陽子   

Mitsuguchi, Takehiro; Okabe, Nobuaki*; Miyake, Masayasu*; Matsubara, Akihiro; Fujita, Natsuko; Watanabe, Takahiro; Kokubu, Yoko

東濃地科学センター・加速器質量分析施設(JAEA-AMS-TONO)において、炭酸カルシウム試料のヨウ素129($$^{129}$$I)分析のための予備試験を実施した。用いた試料はベトナム・コンダオ島産のサンゴ年輪(西暦1946-1947年)である。試料の前処理・分析概要は以下の通りである:(1)1%塩酸による洗浄、(2)17%リン酸による溶解、(3)ICP-MSによるヨウ素濃度分析、(4)ヨウ素標準試料の添加、(5)ヨウ素の溶媒抽出、(6)ヨウ化銀沈澱物の生成、(7)沈澱物とニオブ粉末を混合してプレス後、JAEA-AMS-TONOにて$$^{129}$$Iを分析。なお、前処理過程における$$^{129}$$Iバックグラウンドを評価するために操作ブランク試験も行った。その結果、$$^{129}$$Iバックグラウンドは$$^{129}$$I/$$^{127}$$I比で[4.3$$pm$$0.1]$$times$$10$$^{-14}$$であり、バックグラウンド補正後のサンゴ試料の$$^{129}$$I/$$^{127}$$I比は[1.53$$pm$$0.76]$$times$$10$$^{-12}$$であった。この結果は先行研究の結果と整合的であることから、JAEA-AMS-TONOにおいて炭酸カルシウム試料の$$^{129}$$I分析が確立されたと言える。なお、本件は経済産業省・資源エネルギー庁から委託した「地質環境長期安定性評価技術高度化開発」で得られた成果の一部である。

A preliminary test for AMS $$^{129}$$I measurement of CaCO$$_{3}$$ samples was performed using a tandem Pelletron AMS system at Tono Geoscience Center, Japan Atomic Energy Agency (JAEA-AMS-TONO). An annually-banded coral collected from Vietnam was used for this test. The procedure of the test was as follows: (1) an annual-band sample of AD 1946-47 from the coral was treated with 1% HCl for removal of its surface portion; (2) the treated sample was dissolved in H$$_{3}$$PO$$_{4}$$ solution; (3) an aliquot from the sample solution was used for $$^{127}$$I measurement by ICP-MS; (4) the Woodward iodine standard was added as a carrier to the sample solution; (5) iodine was extracted from the solution by solvent extraction and back-extraction, resulting in an aqueous phase with extracted iodine; (6) AgNO$$_{3}$$(aq) was added to the aqueous phase to obtain AgI precipitate; (7) the AgI precipitate was mixed with Nb and pressed into a copper cathode for $$^{129}$$I measurement by JAEA-AMS-TONO. A blank test of this procedure was also made to evaluate the background $$^{129}$$I effect in the sample preparation. Results we obtained were as follows: (1) the background $$^{129}$$I/$$^{127}$$I ratio was [4.3 $$pm$$ 0.1] $$times$$ 10$$^{-14}$$ and (2) the background-corrected coral $$^{129}$$I/$$^{127}$$I ratio was [1.53 $$pm$$ 0.76] $$times$$ 10$$^{-12}$$. The coral $$^{129}$$I/$$^{127}$$I ratio is generally in agreement with previously-reported values of Chang et al. (2016), suggesting that AMS $$^{129}$$I measurement of CaCO$$_{3}$$ samples has been generally established in JAEA-AMS-TONO.

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