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

Fukuda, Shoma; Kagami, Saya

Fisshion, Torakku Nyusureta, (35), p.11 - 14, 2022/12

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.

Research plan on geosphere stability for long-term isolation of radioactive waste (Scientific program for fiscal year 2022)

Sasao, Eiji; Ishimaru, Tsuneari; Niwa, Masakazu; Shimada, Akiomi; Shimada, Koji; Watanabe, Takahiro; Sueoka, Shigeru; Yokoyama, Tatsunori; Fujita, Natsuko; Ogita, Yasuhiro; et al.

JAEA-Review 2022-022, 29 Pages, 2022/09

JAEA-Review-2022-022.pdf:0.97MB

This report is a plan of research and development (R&D) on geosphere stability for long-term isolation of high-level radioactive waste (HLW) in Japan Atomic Energy Agency (JAEA), in fiscal year 2022. The objectives and contents in fiscal year 2022 are described in detail based on the JAEA 4th Medium- and Long-term Plan (fiscal years 2022-2028). In addition, the background of this research is described from the necessity and the significance for site investigation and safety assessment, and the past progress. The plan 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

Geochemical and heavy mineral signatures of marine incursions by a paleotsunami on the Miyazaki plain along the Nankai-Suruga trough, the Pacific coast of southwest Japan

Watanabe, Takahiro; Kagami, Saya; Niwa, Masakazu

Marine Geology, 444, p.106704_1 - 106704_13, 2022/02

https://doi.org/10.1016/j.margeo.2021.106704

Miyazaki plain on the Pacific coast of southwest Japan along the Nankai-Suruga trough was also affected by marine incursion by the past interplate earthquakes and tsunami. Notably, paleotsunami deposits were found on the area and important clues to reconstruct the past marine incursion by earthquakes and tsunami. However, geochemical and heavy mineral analyses on the area were not enough to characterize the deposits. Therefore, quantification analyses with high-time resolution by portable energy dispersive X-ray fluorescence spectrometry (portable XRF), scanning by X-ray analytical microscope (XGT), statistical analyses for chemical components, and heavy mineral analyses were performed for the paleotsunami deposits of the Kanbun Hyuganada earthquake with the age of 1662 CE from the south Miyazaki plain in this study. Based on our research, we summarized as follows: (1) increases in the titanium normalized values of S, Ca, Fe and Sr, and depletions of Si, K, and Rb were observed in the deposits, (2) Zr accumulations and heavy minerals such as zircon were found in the deposits caused by possible high energy tsunami, and (3) cluster analyses of the geochemical data from the core by portable XRF distinguished the paleotsunami deposits on the Miyazaki plain.

Estimation of denudation history of the Kitakami Mountains based on apatite fission-track thermochronology

Kajita, Yuya*; Sueoka, Shigeru; Fukuda, Shoma; Yokoyama, Tatsunori; Kagami, Saya; Nagata, Mitsuhiro; Tagami, Takahiro*

Fisshion, Torakku Nyusureta, (34), p.14 - 16, 2021/12

For reconstructing the uplift/denudation history of the fore-arc side of the NE Japan Arc on geologic timescales, U-Pb dating and apatite fission-track (AFT) thermochronometry were applied to granitoids in Kitakami mountains. In addition, U-Pb dating for the Jodogahama rhyolite at the easternmost Kitakami mountains was also carried out to estimate the timing of volcanism and its thermal effect. Consequently, U-Pb ages of 122.7 Ma and 117.3 Ma for 2 samples of the Cretaceous granites and AFT ages ranging from 156.8 Ma to 70.3 Ma of 15 samples were obtained. Concerning the Jodogahama rhyolite, U-Pb age of 44.3 Ma was obtained. Integrated AFT data of this study and previous ones in Kitakami mountains, the trend of ages shows younging toward west. Although such age trend can be explained by volcanism of the Jodogahama reflecting the migration of a paleo-volcanic front, all AFT ages exhibited significantly older than U-Pb data of the Jodogahama and the thermal inverse modeling based on track length distributions provided slow cooling patterns. These observations did not supported the reheating of volcanism as a cause of age trend. As future prospects, we are planning to improve the reliability of age data based on additional analyses and apply an ultra low-temperature thermochronometer, e.g., ESR method.

Simultaneous determination of insoluble fluoride-forming and high field-strength element abundances in rock samples by ICP-QMS through isotope dilution-internal standardisation

Kagami, Saya; Yokoyama, Tetsuya*

Geostandards and Geoanalytical Research, 45(4), p.679 - 699, 2021/12

https://doi.org/10.1111/ggr.12394

We developed a new method for the determination of the mass fractions of insoluble fluoride-forming elements (IFFEs) and high field strength elements (HFSEs) in rock samples by ICP-QMS. Unlike conventional methods in which the two elemental groups were measured separately using two solutions prepared from distinct sample aliquots, the new technique prepares a solution by acid digestion from a single sample aliquot, then divide the solution into two fractions that are dedicated to the measurement of IFFEs and HFSEs, respectively. The problem regarding the incorporation of IFFEs/HFSEs into insoluble fluorides during HF digestion was overcome by adjusting the Ca-Al-Mg composition of the sample before acid digestion. The acceptable compositional range was Ca/(Ca+Al) 0.43 and Mg/(Mg+Al) 0.40 when the sample was decomposed on a hot plate, while more restricted condition of Ca/(Ca+Al) 0.40, Mg/(Mg+Al) 0.40, and Al/(Mg+Ca) 1.7 was required for the digestion under high pressure and temperature using Teflon bomb. This method achieved the repeatabilities of 4% for most IFFEs and HFSEs, and yielded the mass fractions of most IFFEs and HFSEs that were consistent with the data obtained by conventional methods within 5%. The method is applicable not only to precious samples but also to heterogeneous samples containing accessory minerals enriched in IFFEs/HFSEs.

Analytical method for chemical compositions of volcanic glasses in Tono Geoscience Center; Quantitative measurements of Major Elements by using EPMA and Minor Elements by LA-ICP-MS

Kagami, Saya; Yokoyama, Tatsunori; Umeda, Koji*

JAEA-Testing 2021-001, 49 Pages, 2021/08

JAEA-Testing-2021-001.pdf:3.86MB

To make a contribution to safety assessment for geological disposal of high level radioactive and/or TRU waste, we need to assess long-term stability of geological environment and predict long-term changes of geotectonic events that will occur in the future, especially for Quaternary period ( 2.6 million years ago-present). In the most case, we investigate chronological data of geological events by radiometric dating. When some geological samples have no objects to which radiometric dating method can be applied (e.g., zircon, biotite, wood fragments and plant residues), we can use tephrochronology, which is geological dating method using each layer of tephra (erupted volcanic ash), for dating of geological layers. This chronological method is essential in Japan, where volcanism is very active. Tephra is usually characterized by petrographic characteristics and/or chemical composition (mainly major elements) of volcanic glasses and/or minerals in tephra. In Tono Geoscience Center (Japan Atomic Energy Agency), we develop an analytical technique of chemical composition including trace elements of volcanic glasses for detailed tephra identification. In this paper, we report a sample preparation procedure and analytical methods of chemical compositions of individual volcanic glass shards by using an electron probe microanalyzer and a laser ablation-inductively coupled plasma-mass spectrometer.

Geochemical and chronological studies of basaltic eucrites; Implications for decoding the thermal history of a terrestrial planet, Vesta

Kagami, Saya

Chikyu Kagaku, 55(2), p.57 - 58, 2021/06

https://doi.org/10.14934/chikyukagaku.55.57

no abstracts in English

Annual report for research on geosphere stability for long-term isolation of radioactive waste in fiscal year 2019

Ishimaru, Tsuneari; Ogata, Nobuhisa; Kokubu, Yoko; Shimada, Koji; Hanamuro, Takahiro; Shimada, Akiomi; Niwa, Masakazu; Asamori, Koichi; Watanabe, Takahiro; Sueoka, Shigeru; et al.

JAEA-Research 2020-011, 67 Pages, 2020/10

JAEA-Research-2020-011.pdf:3.87MB

This annual report documents the progress of research and development (R&D) in the 5th 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.

Research plan on geosphere stability for long-term isolation of radioactive waste (Scientific program for fiscal year 2019)

Ishimaru, Tsuneari; Ogata, Nobuhisa; Hanamuro, Takahiro; Shimada, Akiomi; Kokubu, Yoko; Asamori, Koichi; Niwa, Masakazu; Shimada, Koji; Watanabe, Takahiro; Sueoka, Shigeru; et al.

JAEA-Review 2019-010, 46 Pages, 2019/09

JAEA-Review-2019-010.pdf:2.45MB

This report is a plan of research and development (R&D) on geosphere stability for long-term isolation of high-level radioactive waste (HLW) in Japan Atomic Energy Agency, in fiscal year 2019. The objectives and contents in fiscal year 2019 are described in detail based on the outline of 7 years plan (fiscal years 2015-2021). Background of this research is clarified with the necessity and the significance for site investigation and safety assessment, and the past progress in this report. In addition, the plan 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.

An Analytical technique of trace elements using LA-ICP-MS for tephra identification

Kagami, Saya; Yokoyama, Tatsunori; Umeda, Koji*

no journal, , 

Tephrochronology is one of the geochronological techniques for Quaternary and generally used as well as radiocarbon dating. A catalogue of wide-spread tephras provides fundamental criteria for the establishment of a regional chronostratigraphy. Tephras have been identified by petrographic characteristics, types of volcanic glass shards in tephra, and major elements compositions of them. Major element analyses of volcanic glass shards are usually carried out by EPMA. Recently, it has been reported that the some tephras which were quite similar to others in major element compositions were distinguishable by trace element compositions. Although trace element data of volcanic glass shards are important for tephra identification, the data are still lack in a catalogue of wide-spread tephras. To measure trace element abundances of the glass shards, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) is a powerful method because individual glass shards can be analyzed. In this study, we performed trace element analysis of tephras using LA-ICP-MS at Tono Geoscience Center, JAEA. We analyzed the concentration of 41 elements with the internal standard element of Si and two calibration standards of NIST SRM 612 and 614. Three tephra samples were prepared: Aso-4, Aira-Tn (AT), and Akogi (identified to Znp-Ohta) tephras. While a fused glass bead of Aso-4 was prepared, the others were mounted on epoxy resin. In Aso-4 and AT tephra samples, the concentrations of trace elements (Rb, Sr, Y, Zr, Ba, La, and Ce), by which tephras are especially identified, were consistent with those in the previous studies (RSD:10%). We obtained the pattern of trace element compositions of Akogi tephras, which was similar to that of Znp-Ohta tephras. This analytical method will contribute to establish the detailed catalogue of tephras.