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I/
I and 
C records in a modern coral from Rowley Shoals off northwestern Australia reflect the 20th-century human nuclear activities and ocean/atmosphere circulationsMitsuguchi, Takehiro; Okabe, Nobuaki*; Yokoyama, Yusuke*; Yoneda, Minoru*; Shibata, Yasuyuki*; Fujita, Natsuko; Watanabe, Takahiro; Kokubu, Yoko
Journal of Environmental Radioactivity, 235-236, p.106593_1 - 106593_10, 2021/09
Times Cited Count：5 Percentile：35.21(Environmental Sciences)For a contribution to developing the usage of iodine-129 (I) as a tracer of deep-seated fluid, I/I and C were measured for annual bands (AD 1931-1991) of a modern coral collected from Northwestern Australia; the measurements were performed using the JAEA-AMS-TONO-5MV for I/I and an AMS facility of the University of Tokyo for C. Results indicate that both I/I and C distinctly increase from 1950s. The C increase can be ascribed to atmospheric nuclear tests, while the I/I increase is due to nuclear-fuel reprocessing as well as atmospheric nuclear tests. These results are in good agreement with previous studies, indicating that the I/I measurement by JAEA-AMS-TONO-5MV has been further developed.
C measurement of CaCO
samples and coral-based estimation of marine reservoir correction in the Ogasawara Islands, Northwestern Subtropical PacificKokubu, Yoko; Mitsuguchi, Takehiro*; Watanabe, Takahiro; Yamada, Tsutomu*; Asami, Ryuji*; Iryu, Yasufumi*
Radiocarbon, 61(5), p.1593 - 1601, 2019/10
Times Cited Count：1 Percentile：5.84(Geochemistry & Geophysics)We performed C measurements of two fossil and one modern corals using a combined system of an elemental analyzer and an automated graphitization equipment AGE3 (EA-AGE3 system) and JAEA-AMS-TONO. The C concentrations (pMC values) of mid-Holocene Okinawa corals obtained by our EA-AGE3 system appear to be slightly higher than those obtained by the conventional graphitization method using phosphoric acid. The pMC increase in our EA-AGE3 system may result in significant underestimation of C age especially for older samples (e.g., 10,000 BP); however, the pMC increase is negligible in C measurements of modern or recent samples. We applied the EA-AGE3 method to the pre- and post-bomb annual-band samples from the modern Ogasawara coral for C measurements. On the basis of the pre-bomb coral C data, we estimated marine reservoir correction (R) around Ogasawara Islands and its stability between 
1900 and 1950 AD.
Yokoyama, Tatsunori; Kimura, Junichi*; Mitsuguchi, Takehiro; Danhara, Toru*; Hirata, Takafumi*; Sakata, Shuhei*; Iwano, Hideki*; Maruyama, Seiji*; Chang, Q.*; Miyazaki, Takashi*; et al.
Geochemical Journal, 52(6), p.531 - 540, 2018/12
Times Cited Count：17 Percentile：65.79(Geochemistry & Geophysics)Yokoyama, Tatsunori; Kokubu, Yoko; Murakami, Hiroaki; Watanabe, Takahiro; Mitsuguchi, Takehiro
no journal, ,
no abstracts in English
Yokoyama, Tatsunori; Kokubu, Yoko; Mitsuguchi, Takehiro; Murakami, Hiroaki; Hirata, Takafumi*; Sakata, Shuhei*; Danhara, Toru*; Iwano, Hideki*; Maruyama, Seiji*; Chang, Q.*; et al.
no journal, ,
no abstracts in English
Yokoyama, Tatsunori; Kokubu, Yoko; Mitsuguchi, Takehiro; Murakami, Hiroaki; Hirata, Takafumi*; Sakata, Shuhei*; Danhara, Toru*; Iwano, Hideki*; Maruyama, Seiji*; Miyazaki, Takashi*; et al.
no journal, ,
Chronological and geochemical studies of calcium carbonates can provide precious information for changes in geochemical condition in deep geological environments. Because the carbonate can be found as common filling minerals in rocks, age zoning and spatial distribution of chemical composition in the carbonate could be a wide-use indicator to reconstruct the past environmental changes. Calcite and other carbonate materials have been dated by Isotope Dilution-Thermal Ionization Mass Spectrometry. On the other hand, a few of U-Pb dating studies in a micro scale area (less than 10 micrometer) such as using laser ablation-multiple collector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) has been conducted on the carbonate. The U-Pb dating technique for the carbonates using LA-MC-ICPMS is still immature partly because of a lack of consensus international carbonate reference materials for the in-situ dating technique. In order to solve this problem, we performed a survey on the carbonate reference materials that may be suitable for high precision U-Pb dating using LA-MC-ICPMS. Additionally, we conducted experiments to make compositionally homogeneous carbonate (calcite) reference materials.
Yokoyama, Tatsunori; Kokubu, Yoko; Mitsuguchi, Takehiro*; Murakami, Hiroaki; Hirata, Takafumi*; Sakata, Shuhei*; Danhara, Toru*; Iwano, Hideki*; Maruyama, Seiji*; Chang, Q.*; et al.
no journal, ,
no abstracts in English
Yokoyama, Tatsunori; Mitsuguchi, Takehiro; Sueoka, Shigeru
no journal, ,
In recent years, it has become possible to carry out high-precision microscale age dating of geological samples using developed micro-analytical techniques such as SIMS, LA-ICP-MS, etc. Application of LA-ICP-MS-based microscale U-Pb dating is extending from U-rich heavy minerals such as zircon, apatite and monazite to U-depleted minerals such as calcite. This kind of method enables age determination of several types of mineral grains occurring within rock bodies, and thereby reveals chronological changes in chemical composition of source materials from which the minerals were crystallized, with some cases in which thermal history of the crystal formation system can be reconstructed. For research and development of geological disposal techniques for high-level radioactive wastes, we develop and facilitate geochronological dating techniques for evaluation of long-term stability in geological environments, at Tono Geoscience Center, Japan Atomic Energy Agency. In our presentation, we introduce the current status of our development for research on long-term stability of geological environments, U-Pb dating of calcite, U-Pb dating of young zircon and trace element analysis by using LA-ICP-MS.
I measurement of CaCO samples in JAEA-AMS-TONOMitsuguchi, Takehiro; Okabe, Nobuaki*; Miyake, Masayasu*; Matsubara, Akihiro; Fujita, Natsuko; Watanabe, Takahiro; Kokubu, Yoko
no journal, ,
A preliminary test for AMS I measurement of CaCO 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 HPO
solution; (3) an aliquot from the sample solution was used for 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(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 I measurement by JAEA-AMS-TONO. A blank test of this procedure was also made to evaluate the background I effect in the sample preparation. Results we obtained were as follows: (1) the background I/I ratio was [4.3 
0.1] 
10
and (2) the background-corrected coral I/I ratio was [1.53 0.76] 10
. The coral I/I ratio is generally in agreement with previously-reported values of Chang et al. (2016), suggesting that AMS I measurement of CaCO samples has been generally established in JAEA-AMS-TONO.
Yokoyama, Tatsunori; Yuguchi, Takashi*; Sakata, Shuhei*; Ishibashi, Kozue*; Ogita, Yasuhiro*; Ito, Daichi*; Ono, Takeshi*; Kagami, Saya; Mitsuguchi, Takehiro; Sueoka, Shigeru
no journal, ,
Dating and trace elements analysis of zircons provide us the evidences of past thermal history about their growth events, such as timing and temperature of magmatism and crystallization. In granitic rocks, because the proposed closure temperature of zircon U-Pb (
900 
C) is often higher than crystallization temperature of the zircon, the zircon U-Pb age means the timing of crystallization. To clarify the growth history of granitic pluton, Yuguchi et al. (2016) performed the observation of internal structure of zircon (collected from the Toki granite, central Japan) using cathodoluminescence, deriving crystallization temperature and age using Ti-in-zircon thermometry and U-Pb dating. It is important to discuss the emplacement by such an approach to understand the history of upheaval and exhumation of igneous complex. In this study, for simultaneously estimating crystallization age and temperature of zircon, we performed U-Pb isotopic analysis and quantitative analysis of Titanium, in the same position of zircon, using LA-ICP-MS after the cathodoluminescence observation. As preliminary experiments, we analyzed zircons collected from Japan (e.g., Okue, Tono, Toki and Kurobegawa granites) to estimate their thermal history. We could estimate the crystallization ages and temperatures of zircons of Okue (556-946C in 11.1-16.1 Ma), Tono (613-901C in 110.2-127.4 Ma), Toki (575-734C in 69.4-79.9 Ma) and Kurobegawa (636-779C in 0.46-1.85 Ma), respectively.
