Evaluating sulfur-impurity removal and modern carbon contamination in different preparation methods for radiocarbon dating of soil samples by accelerator mass spectrometry

Koarashi, Jun; Takeuchi, Erina; Kokubu, Yoko; Atarashi-Andoh, Mariko

Radiocarbon, 67(2), p.307 - 317, 2025/04

https://doi.org/10.1017/RDC.2024.137

Radiocarbon (C) dating of soil samples by accelerator mass spectrometry has been proven useful for studying carbon (C) cycling in terrestrial ecosystems. There are, however, two main difficulties in sample preparation for this application: contamination of samples with modern C and inhibition of graphite formation due to sulfur (S)-containing impurities. Here we evaluated these effects from three different sample preparation methods, by conducting C measurements of C-dead sample and S-rich soil samples. The preparation methods were all successful in graphite formation and C measurement for soil samples with an organic S content 6.9%. The different methods showed different percent Modern Carbon (pMC) values ranging from 0.19% to 0.64% for C-dead sample. However, the three methods had little influence on the determination of C age for samples at least younger than 12,000 yr BP. The methods examined in the present study can be used for C dating with sufficient accuracy in the application to C cycle studies.

Results of environmental impact investigations as part of environmental monitoring investigation in backfilling of shafts and tunnels of Mizunami Underground Research Laboratory (FY2023)

Takeuchi, Ryuji; Kokubu, Yoko; Nishio, Kazuhisa*

JAEA-Data/Code 2024-015, 68 Pages, 2025/02

JAEA-Data-Code-2024-015.pdf:4.25MB

The Tono Geoscience Center of Japan Atomic Energy Agency (JAEA) has been conducting the environmental monitoring investigation to confirm the environmental impacts associated with the backfilling of shafts and tunnels at the Mizunami Underground Research Laboratory (MIU). This report summarizes the results of the environmental impact investigations conducted as part of the environmental monitoring investigation around the MIU Site in FY2023, which include groundwater level measurement in wells, river flow rate measurement, water analysis of Hazama river, noise and vibration surveys, and soil survey.

A Review and interpretation of iodine-129 in Earth's surface layers; Towards evaluating the long-term stability of geological environments

Mitsuguchi, Takehiro; Okabe, Nobuaki*; Kokubu, Yoko; Matsuzaki, Hiroyuki*

Genshiryoku Bakkuendo Kenkyu (CD-ROM), 31(2), p.96 - 110, 2024/12

https://doi.org/10.3327/jnuce.31.2_96

Geological disposal of high-level radioactive waste requires not only selecting sites appropriate for the waste repository, where its isolation ability would not be damaged by natural phenomena for several tens of thousands of years, but also rationally constructing the disposal system depending on site-specific geological environments and their anticipated long-term variability. Recently, elemental/isotopic compositions of underground fluids (deep groundwaters, hot/cold spring waters, brines associated with oil and natural gas reservoirs, and so on) in Japan have been studied for evaluating the long-term stability of the geological environments of this country. Iodine and its radioactive isotope I (half-life = 15.7 million years) are included in the subjects of the study. The current review paper provides overviews of (i) the iodine content and iodine-129/127 ratio (I/I ratio) of various materials in Earth's surface layers, (ii) relevant sample pretreatments and measurements, and (iii) I/I data of the underground fluids in Japan, then gives (iv) some interpretations of the fluid I/I data, along with their problems and uncertainties, and (v) some implications towards evaluating the long-term stability of geological environments.

Results of environmental impact investigations as part of environmental monitoring investigation in backfilling of shafts and tunnels of Mizunami Underground Research Laboratory (2022)

Takeuchi, Ryuji; Nishio, Kazuhisa*; Kokubu, Yoko

JAEA-Data/Code 2023-013, 74 Pages, 2024/01

JAEA-Data-Code-2023-013.pdf:4.2MB

The Tono Geoscience Center of Japan Atomic Energy Agency (JAEA) has been conducting the environmental monitoring investigation to confirm the environmental impacts associated with the backfilling of shafts and tunnels at the Mizunami Underground Research Laboratory (MIU). This report summarizes the results of the environmental impact investigations conducted as part of the environmental monitoring investigation around the MIU Site in FY2022, which include groundwater level measurement in wells, river flow rate measurement, water analysis of Hazama river, noise and vibration surveys, and soil survey.

Be analysis of the rock samples from the northeastern shore of Lake Pumoyum Co in south Tibetan Plateau

Nara, Fumiko*; Watanabe, Takahiro; Kokubu, Yoko; Zhu, L.*

Nuclear Instruments and Methods in Physics Research B, 539, p.28 - 32, 2023/06

https://doi.org/10.1016/j.nimb.2023.03.007

Lake Pumoyum Co is located on the south Tibetan Plateau. The lake terraces are developed on the eastern lake shore, and it supposed that the large lake level changes would have happened in Pumoyum Co. The in-situ terrestrial cosmogenic adionuclides can be used to estimate the earth surface processes, such as the erosion rate and exposure age dating of rocks. Here we report the results of Be values of the rock samples from the lake terraces around Pumoyum Co. The concentrations of Be were measured by the JAEA-AMS-TONO-5MV in the Tono Geoscience Center, Japan Atomic Energy Agency. The Be concentrations ranged from 3.78 to 10.810 (atoms/g), but the Be values showed the decreasing trend following to the distance from the lake shore. This result indicates that Be values of the rocks at the shore of Pumoyum Co could be influenced from the erosion rate or tectonic process rather than the exposure date resulting from the lake level changes.

Results of environmental impact investigations as part of environmental monitoring investigation in backfilling of shafts and tunnels of Mizunami Underground Research Laboratory (2020-2021)

Takeuchi, Ryuji; Nishio, Kazuhisa*; Hanamuro, Takahiro; Kokubu, Yoko

JAEA-Data/Code 2022-010, 110 Pages, 2023/03

JAEA-Data-Code-2022-010.pdf:6.2MB

The Tono Geoscience Center of Japan Atomic Energy Agency (JAEA) has been conducting the environmental monitoring investigation to confirm the environmental impacts associated with the backfilling of shafts and tunnels at the Mizunami Underground Research Laboratory (MIU). This report summarizes the results of environmental impact investigations conducted as part of the environmental monitoring investigation around the MIU Site from FY2020 to FY2021, which include groundwater level measurement in wells, river flow rate measurement, water analysis of Hazama river, noise and vibration surveys, and soil survey.

Separation of quartz for measurement of beryllium-10 and aluminium-26; Application of cell handler

Kokubu, Yoko; Utsumi, Yoshinori*; Ito, Saburo*; Shimada, Koji

Dai-23-Kai AMS Shimpojiumu Hokokushu, p.60 - 63, 2022/12

In the case of estimating erosion rates of ground surfaces from measurement of beryllium-10 and aluminum-26, quartz contained in rocks and sediments is used as a measurement sample. In this paper, we present an example of separating quartz using a cell handler, which is a cell separation system, without chemical treatment using hydrofluoric acid. By optimizing the way to apply light to the mineral sample with the cell handler and the exposure time of the camera of the cell handler, quartz and other minerals, such as feldspar, were able to be distinguished from other minerals, such as feldspar in image recognition. An experimental measurement using rock samples was then performed under these conditions. As a result, only quartz was successfully separated through a fully automatized process by that distinguishes and picks quartz using the image recognition software and picking system built into the cell handler.

Project for development of a downsized AMS system based on the surface stripper technique

Fujita, Natsuko; Matsubara, Akihiro; Kimura, Kenji; Jinno, Satoshi; Kokubu, Yoko

Nuclear Instruments and Methods in Physics Research B, 532, p.13 - 18, 2022/12

https://doi.org/10.1016/j.nimb.2022.09.011

Over the last decade, significant technological advances were made to downsize the AMS systems. Japan Atomic Energy Agency has started a project for developing a prototype downsized AMS system (with the footprint of the system is 1.9 m 1.9 m) based on the surface stripper technique. Although the system configuration using an ion source, magnets, and detectors is similar to that in conventional systems, there is no tandem accelerator as well as a gas stripper. The ion acceleration is provided in the ion source (maximum ion energy 40 keV). For proof-of-principle experiments, we have planned two steps: (1) Observation of the specular reflection and the dissociation by using a compact electrostatic analyzer located just behind the stripper, and (2) Demonstration of C measurement, along with the experimental confirmation of the isobar suppression capability of the surface stripper.

Present status of the JAEA-AMS-TONO (2019-2020)

Fujita, Natsuko; Matsubara, Akihiro; Miyake, Masayasu*; Watanabe, Takahiro; Kokubu, Yoko; Nishio, Tomohiro*; Ogawa, Yumi*; Kato, Motohisa*; Shimada, Akiomi; Ogata, Nobuhisa

Dai-33-Kai Tandemu Kasokuki Oyobi Sono Shuhen Gijutsu No Kenkyukai Hokokushu, P. 48, 2022/04

no abstracts in English

Annual report for research on geosphere stability for long-term isolation of radioactive waste in fiscal year 2020

Ishimaru, Tsuneari; Ogata, Nobuhisa; Kokubu, Yoko; Shimada, Koji; Niwa, Masakazu; Shimada, Akiomi; Watanabe, Takahiro; Sueoka, Shigeru; Yokoyama, Tatsunori; Fujita, Natsuko; et al.

JAEA-Research 2021-007, 65 Pages, 2021/10

JAEA-Research-2021-007.pdf:4.21MB

This annual report documents the progress of research and development (R&D) in the 6th fiscal year during the JAEA 3rd Mid- and Long-term Plan (fiscal years 2015-2021) to provide the scientific base for assessing geosphere stability for long-term isolation of the high-level radioactive waste. The planned framework is structured into the following categories: (1) Development and systematization of investigation techniques, (2) Development of models for long-term estimation and effective assessment, (3) Development of dating techniques. The current status of R&D activities with previous scientific and technological progress is summarized.