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Journal Articles

Geochronological study of the Atokura Formation and contact igneous rocks in Shimonita-machi, Gunma Prefecture, central Japan

Bando, Koki*; Nagata, Mitsuhiro; Asahara, Yoshihiro*; Ishizaki, Yasuo*; Oto, Shigeru*

Shimonitamachi Shizenshikan Kenkyu Hokoku, (8), p.33 - 53, 2023/03

We studied the geochronology and geochemistry of the Cretaceous Atokura Formation called Atokura nappe and intrusive rocks in Shimonita, Gunma Prefecture. The depositional age of the Atokura Formation has not been determined whether it was the Early Cretaceous (Barremian) or Late Cretaceous (Cenomanian-Campanian). The youngest cluster dates obtained from 4 sandstone samples of the Atokura Formation are 182.8 Ma, 129.8 Ma, 123.7 Ma, and 115.1 Ma. Zircons from igneous rocks in the Atokura Formation yielded U-Pb ages of 123.2 Ma, and their zircons show $$varepsilon$$Hf(t)=3.0 to 3.8. The depositional age of the Atokura Formation generally supported the Barremian, but younger zircon U-Pb date was obtained from one sample. The intrusive rocks are similar to the U-Pb dates and Hf isotopes of zircons obtained from Kitakami or Abukuma granitoids in NE Japan.

Journal Articles

Mesospheric ionization during substorm growth phase

Murase, Kiyoka*; Kataoka, Ryuho*; Nishiyama, Takanori*; Nishimura, Koji*; Hashimoto, Taishi*; Tanaka, Yoshimasa*; Kadokura, Akira*; Tomikawa, Yoshihiro*; Tsutsumi, Masaki*; Ogawa, Yasunobu*; et al.

Journal of Space Weather and Space Climate (Internet), 12, p.18_1 - 18_16, 2022/06

 Times Cited Count:0 Percentile:24.42(Astronomy & Astrophysics)

We identified two energetic electron precipitation (EEP) events during the growth phase of moderate substorms and estimated the mesospheric ionization rate for an EEP event for which the most comprehensive dataset from ground-based and space-born instruments was available. The mesospheric ionization signature reached below 70 km altitude and continued for ~15 min until the substorm onset, as observed by the PANSY radar and imaging riometer at Syowa Station in the Antarctic region. We also used energetic electron flux observed by the Arase and POES 15 satellites as the input for the air-shower simulation code PHITS to quantitatively estimate the mesospheric ionization rate. Combining the cutting-edge observations and simulations, we shed new light on the space weather impact of the EEP events during geomagnetically quiet times, which is important to understand the possible link between the space environment and climate.

Journal Articles

Characteristics in trace elements compositions of tephras (B-Tm and To-a) for identification tools

Nara, Fumiko*; Yokoyama, Tatsunori; Yamasaki, Shinichi*; Minami, Masayo*; Asahara, Yoshihiro*; Watanabe, Takahiro; Yamada, Kazuyoshi*; Tsuchiya, Noriyoshi*; Yasuda, Yoshinori*

Geochemical Journal, 55(3), p.117 - 133, 2021/00

 Times Cited Count:5 Percentile:58.66(Geochemistry & Geophysics)

The absolute date of the Millennium Eruption (ME) of Changbaishan Volcano is widely recognized as AD 946. The Baegdosan-Tomakomai (B-Tm) tephra dispersed during the ME is a robust-age key bed. In order to identify the tephra, refractive index and major-element compositions of volcanic glass shards are conventionally used. However, trace-element analysis has been rarely carried out, especially for rare-earth elements (REEs) and for tephra layer bulk sediments. Here we present the datasets of major- and trace-element compositions datasets for the glass shards and bulk sediments of the B-Tm and Towada caldera eruptions (To-a) tephra deposits from the Lake Ogawara sediment core, Tohoku region, northern Japan. The depth profiles of the major and trace elements show the significant peaks for the K$$_{2}$$O and some trace elements (Zn, Rb, Zr, Nb, Sn, Y, La, Ce, Nd, Th, and U) at the B-Tm tephra layer in the Lake Ogawara sediment core, but no peaks of these elements at the To-a tephra layer. High concentrations of the trace elements in the B-Tm tephra layer were observed in individual glass shards as well as in the bulk sediment. These concentrations are highlighted by the elemental abundance pattern normalized by the crustal abundance. The elemental pattern in individual glass shards from other Japanese tephras showed significant differences from those of the B-Tm tephra, especially in REEs compositions. The trace-element compositions of the glass shards and bulk sediment show strong advantages for distinguishing the B-Tm tephra from other Japanese tephras.

Journal Articles

Transient ionization of the mesosphere during auroral breakup; Arase satellite and ground-based conjugate observations at Syowa Station

Kataoka, Ryuho*; Nishiyama, Takanori*; Tanaka, Yoshimasa*; Kadokura, Akira*; Uchida, Herbert Akihito*; Ebihara, Yusuke*; Ejiri, Mitsumu*; Tomikawa, Yoshihiro*; Tsutsumi, Masaki*; Sato, Kaoru*; et al.

Earth, Planets and Space (Internet), 71(1), p.9_1 - 9_10, 2019/12

 Times Cited Count:7 Percentile:40.92(Geosciences, Multidisciplinary)

Transient ionization of the mesosphere was detected at around 65 km altitude during the isolated auroral expansion occurred at 2221-2226 UT on June 30, 2017. A general-purpose Monte Carlo particle transport code PHITS suggested that significant ionization is possible in the middle atmosphere due to auroral X-rays from the auroral electrons of $$<$$10 keV.

Journal Articles

Micro-PIXE for the study of atmospheric environment

Kasahara, Mikio*; Ma, C.-J.*; Okumura, Motonori*; Kojima, Takuji; Hakoda, Teruyuki; Taguchi, Mitsumasa; Sakai, Takuro; Ohara, Yoshihiro

JAEA-Review 2005-001, TIARA Annual Report 2004, p.293 - 295, 2006/01

Artificial cloud generation experiment was performed using a huge vertical pit located in Kamaishi iron-copper mine to investigate the characteristics of cloud. The physical and chemical properties of individual cloud droplets were examined by microscopic analysis at Kyoto university and micro-PIXE analysis at TIARA. The process of growth of cloud was clarified based on the result on droplet size, its distribution, droplet number concentration, and the change in distribution of chlorine in droplet as the function of size.

Journal Articles

Micro-PIXE technique for the study of asian dust sources

Kasahara, Mikio*; Ma, C.-J.*; Okumura, Motonori*; Kojima, Takuji; Hakoda, Teruyuki; Taguchi, Mitsumasa; Sakai, Takuro; Ohara, Yoshihiro

JAERI-Review 2004-025, TIARA Annual Report 2003, p.256 - 258, 2004/11

As the source of Asian dust particles, the sands at four different desert areas in China were to be the target of bulk and single analyses by means of PIXE and micro-PIXE analyses, respectively. The physical properties of desert sands like morphology, color, and size were basically determined. Also the chemical characteristics of bulk sands of each desert were specified as the relative elemental mass. The elemental maps and spectra for individual sands allow us to understand the nature of individual sands. Consequently, the physicochemical properties of desert sands obtained from this study can be helpful to understand what kinds of man-made pollutants and sea-salts are incorporated into natural Asian dust particles.

Journal Articles

Conceptual design of a 2 MeV neutral beam injection system for the Steady State Tokamak Reactor

Mizuno, Makoto; Hanada, Masaya; Inoue, Takashi; Ohara, Yoshihiro; Okumura, Yoshikazu; Tanaka, Shigeru; Watanabe, Kazuhiro; Asahara, Masaharu*; *; *; et al.

Fusion Engineering and Design, 23, p.49 - 55, 1993/00

 Times Cited Count:3 Percentile:38.1(Nuclear Science & Technology)

no abstracts in English

Oral presentation

Evaluation of the tube-voltage dependence of organ doses in X-ray CT scans using Monte-Carlo calculation

Koba, Yusuke*; Matsumoto, Shinnosuke*; Nakada, Yoshihiro*; Kasahara, Tetsuji*; Akahane, Keiichi*; Okuda, Yasuo*; Sato, Kaoru; Takahashi, Fumiaki; Yoshitake, Takayasu*; Hasegawa, Takayuki*; et al.

no journal, , 

Many of the CT devices are in Japan. It is guessed that exposure doses of Japanese derived from CT scans are higher than others. Thus, it is needed to properly manage scan conditions and exposure doses of individual patients. JAEA developed WAZA-ARI under the collaboration research project with the National Institute of Radiological Sciences (NIRS) and the Oita University of Nursing and Health Sciences. Practical use of new version WAZA-ARI named WAZA-ARIv2 began on January 30, 2015 at the web server in NIRS. In WAZA-ARIv2, users can calculate patients doses by using only standard condition (120 kV) of X-tube voltage. In recent years, CT scans at low tube voltage against pediatric patients with high radiosensitivity are increasing. In this study, spectrum of X-ray derived from CT scan at low tube voltage was examined, and was defined in "usrsors.f" file of PHITS. We reported the characteristics of X-ray and organ doses derived from CT scan at low tube voltage (80 kV).

Oral presentation

Analysis of effects of body sizes on organ doses due to CT examinations by using voxel phantoms

Sato, Kaoru; Takahashi, Fumiaki; Koba, Yusuke*; Ono, Koji*; Yoshitake, Takayasu*; Hasegawa, Takayuki*; Katsunuma, Yasushi*; Kasahara, Tetsuji*; Okuda, Yasuo*; Nakada, Yoshihiro*; et al.

no journal, , 

JAEA is now developing CT dose calculator named WAZA-ARIv2 in cooperation with the National Institute of Radiological Sciences. WAZA-ARIv2 has been opened to the public as full-dress uses on January 2015. WAZA-ARIv2 can perform dose assessment against 4 different body physiques by using the organ dose database, which were constructed on the basis of adult Japanese phantoms with 4 body sizes (-2$$sigma$$, average, +2$$sigma$$, +5$$sigma$$). In this study, it was found that salivary gland doses are independent on BMI, whereas lung doses are dependent on BMI. The differences in the effects of BMI on absorbed doses between salivary glands and lungs might be caused by the difference in thickness of subcutaneous soft tissues between head and thorax.

Oral presentation

Analysis of organ doses by CT diagnosis for patients of optional physique by using voxel phantoms

Sato, Kaoru; Takahashi, Fumiaki; Koba, Yusuke*; Ono, Koji*; Yoshitake, Takayasu*; Hasegawa, Takayuki*; Katsunuma, Yasushi*; Kasahara, Tetsuji*; Okuda, Yasuo*; Nakada, Yoshihiro*; et al.

no journal, , 

WAZA-ARIv2 is developed as the web-based open system for CT dose calculator under joint research of JAEA, NIRS (now, QST) and Oita University of Nursing and Health Sciences. WAZA-ARIv2 can provide organ doses under consideration of the body physiques (BMI = 18, 22, 28, 37) of patients with average height of adult Japanese by using voxel phantoms developed by JAEA. In this study, we analyzed the relationship between variations of organ doses and body indices. It was found that effects of weight variations on organ doses were larger than those of height variations. Generally, thickness of the subcutaneous soft tissues is easily changed by variations of weight rather than those of height. This fact may cause the differences in variations of organ doses between weight and height.

Oral presentation

Spherical concretion formation; Understandings and applications

Yoshida, Hidekazu*; Yamamoto, Koshi*; Maruyama, Ippei*; Asahara, Yoshihiro*; Minami, Masayo*; Shirono, Shinichi*; Hasegawa, Hitoshi*; Katsuta, Nagayoshi*; Nishimoto, Shoji*; Muramiya, Yusuke*; et al.

no journal, , 

no abstracts in English

Oral presentation

In-situ feasibility experiment for self-sealing process of EDZ and flow-paths factures learnt from spherical carbonate concretion formation

Yoshida, Hidekazu*; Yamamoto, Koshi*; Asahara, Yoshihiro*; Karukaya, Koichi*; Saito, Akane*; Matsui, Hiroya

no journal, , 

no abstracts in English

Oral presentation

Rapid sealing of bed rock flow paths by a synthetic concentration forming solvent

Yoshida, Hidekazu*; Yamamoto, Koshi*; Asahara, Yoshihiro*; Karukaya, Koichi*; Matsui, Hiroya; Metcalfe, R.*

no journal, , 

The ability of synthetic concretion-forming solvents to seal groundwater flow-paths by rapid precipitation of CaCO$$_{3}$$ in bed rock flow-paths has been tested by an in-situ experiment in the underground research laboratory (URL) located in Horonobe, northern Hokkaido, Japan. The experiment showed a decrease in permeability to as low as 1/100 to 1/1,000 of the initial permeability over a period of one year. This sealing process can be applied to various activities that require long-term containment of materials underground, for example abandonment of boreholes connected with hydrocarbon extraction, or CO$$_{2}$$ injection, or sealing of facilities for geological disposal of nuclear wastes.

Oral presentation

In situ experiment for the technology for sealing to underground cavities by a synthetic concretion-forming solvent; Rapid re-sealing of bed rock flow-paths after a earthquake

Yoshida, Hidekazu*; Yamamoto, Koshi*; Asahara, Yoshihiro*; Karukaya, Koichi*; Saito, Akane*; Matsui, Hiroya; Mochizuki, Akihito

no journal, , 

The report are the results of the in situ experiment for sealing to underground cavities by a synthetic concretion-forming solvent and observed phenomenon of the sealing function after a earthquake.

Oral presentation

In-situ feasibility experiment for self-sealing process of EDZ and flow-paths factures learnt from spherical carbonate concretion formation, 2

Yoshida, Hidekazu*; Yamamoto, Koshi*; Asahara, Yoshihiro*; Karukaya, Koichi*; Saito, Akane*; Matsui, Hiroya; Mochizuki, Akihito

no journal, , 

This report summarized the latest results of in-situ feasibility experiment for self-sealing process of EDZ and flow-paths factures in Horonobe URL of JAEA and calsite crystallization induced by concretion-forming solvent injection was observed on the fracture surface in EDZ.

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