Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

https://doi.org/10.1038/s41550-020-01271-2

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

Summary of instructor training program in FY2014 aiming at Asian countries introducing nuclear technologies for peaceful use (Contract program)

Hidaka, Akihide; Nakano, Yoshihiro; Watanabe, Yoko; Arai, Nobuyoshi; Sawada, Makoto; Kanaizuka, Seiichi*; Katogi, Aki; Shimada, Mayuka*; Ishikawa, Tomomi*; Ebine, Masako*; et al.

JAEA-Review 2016-011, 208 Pages, 2016/07

JAEA-Review-2016-011-01.pdf:33.85MB
JAEA-Review-2016-011-02.pdf:27.68MB

JAEA has been conducting the Instructor Training Program (ITP) since 1996 under the auspices of MEXT to contribute to human resource development in currently 11 Asian countries in the field of radiation utilization for seeking peaceful use of nuclear energy. ITP consists of Instructor Training Course (ITC), Follow-up Training Course (FTC) and Nuclear Technology Seminars. In the ITP, trainings or seminars relating to technology for nuclear utilization are held in Japan by inviting nuclear related people from Asian countries to Japan and after that, the past trainees are supported during FTC by dispatching Japanese specialists to Asian countries. News Letter is also prepared to provide the broad range of information obtained through the trainings for local people near NPPs in Japan. The present report describes the activities of FY2014 ITP and future challenges for improving ITP more effectively.

Enhancement of the methodology of repository design and post-closure performance assessment for preliminary investigation stage, 3; Progress report on NUMO-JAEA collaborative research in FY2013 (Joint research)

Shibata, Masahiro; Sawada, Atsushi; Tachi, Yukio; Makino, Hitoshi; Wakasugi, Keiichiro; Mitsui, Seiichiro; Kitamura, Akira; Yoshikawa, Hideki; Oda, Chie; Ishidera, Takamitsu; et al.

JAEA-Research 2014-030, 457 Pages, 2015/03

JAEA-Research-2014-030.pdf:199.23MB

JAEA and NUMO have conducted a collaborative research work which is designed to enhance the methodology of repository design and post-closure performance assessment in preliminary investigation stage. With regard to (1) study on rock suitability in terms of hydrology, based on some examples of developing method of hydro-geological structure model, acquired knowledge are arranged using the tree diagram, and model uncertainty and its influence on the evaluation items were discussed. With regard to (2) study on scenario development, the developed approach for "defining conditions" has been reevaluated and improved from practical viewpoints. In addition, the uncertainty evaluation for the effect of use of cementitious material, as well as glass dissolution model, was conducted with analytical evaluation. With regard to (3) study on setting radionuclide migration parameters, based on survey of precedent procedures, multiple-approach for distribution coefficient of rocks was established, and the adequacy of the approach was confirmed though its application to sedimentary rock and granitic rock. Besides, an approach for solubility setting was developed including the procedure of selection of solubility limiting solid phase. The adequacy of the approach was confirmed though its application to key radionuclides.

Enhancement of the methodology of repository design and post-closure performance assessment for preliminary investigation stage, 2; Progress report on NUMO-JAEA collaborative research in FY2012 (Joint research)

Shibata, Masahiro; Sawada, Atsushi; Tachi, Yukio; Hayano, Akira; Makino, Hitoshi; Wakasugi, Keiichiro; Mitsui, Seiichiro; Oda, Chie; Kitamura, Akira; Osawa, Hideaki; et al.

JAEA-Research 2013-037, 455 Pages, 2013/12

JAEA-Research-2013-037.pdf:42.0MB

Following FY2011, JAEA and NUMO have conducted a collaborative research work which is designed to enhance the methodology of repository design and performance assessment in preliminary investigation stage. With regard to (1) study on rock suitability in terms of hydrology, the tree diagram of methodology of groundwater travel time has been extended for crystalline rock, in addition, tree diagram for sedimentary rock newly has been organized. With regard to (2) study on scenario development, the existing approach has been improved in terms of a practical task, and applied and tested for near field focusing on the buffer. In addition, the uncertainty of some important processes and its impact on safety functions are discussed though analysis. With regard to (3) study on setting radionuclide migration parameters, the approaches for parameter setting have been developed for sorption for rocks and solubility, and applied and tested through parameter setting exercises for key radionuclides.

Innate immune genes including a mucin-like gene, , induced by ionizing radiation in

Kimura, Takafumi*; Takanami, Takako*; Sakashita, Tetsuya; Wada, Seiichi*; Kobayashi, Yasuhiko; Higashitani, Atsushi*

Radiation Research, 178(4), p.313 - 320, 2012/10

https://doi.org/10.1667/RR2989.1

Here, we found that exposure to ionizing radiation (IR) induce certain innate immune response gene of in the intestine. Pre-treatment with IR before seeding on lawn plate, significantly increased survival rate in the nematode. IR induction of gene was highly dependent on the ELT-2 transcription factor and p38 MAPK. Moreover, the insulin/IGF-1 signal pathway works as an enhancer of induction of this gene. Silencing of the gene led to growth retardation after IR irradiation. Finally, we describe the cross-tolerance between the responses to radiation exposure and innate immune system.

Behavioral resistance of against high-LET radiation exposure

Sakashita, Tetsuya; Suzuki, Michiyo; Hamada, Nobuyuki*; Shimozawa, Yoko; Fukamoto, Kana*; Yokota, Yuichiro; Sora, Sakura*; Kakizaki, Takehiko*; Wada, Seiichi*; Funayama, Tomoo; et al.

Biological Sciences in Space, 26, p.7 - 11, 2012/07

https://doi.org/10.2187/bss.26.7

Here, we investigated the resistance to high-LET radiation exposure for two behaviors of the nematode, , which is known as a model organism for the nervous system. Tested behaviors were locomotion and chemotaxis to NaCl. In addition, egg hatchability was examined as an indicator of high-LET radiation sensitivity. Relative biological effectiveness (RBE) of high-LET radiation (C, 18.3 MeV/u, LET = 113 keV/m) relative to low-LET radiation for hatchability was 4.5, whereas RBEs for locomotion and chemotaxis were 1.4 and 1.1, respectively. This study shows that the behavioral system for locomotion and chemotaxis of is highly resistant to high-LET radiation exposure.

Conceptual design of multipurpose compact research reactor; Annual report FY2010 (Joint research)

Imaizumi, Tomomi; Miyauchi, Masaru; Ito, Masayasu; Watahiki, Shunsuke; Nagata, Hiroshi; Hanakawa, Hiroki; Naka, Michihiro; Kawamata, Kazuo; Yamaura, Takayuki; Ide, Hiroshi; et al.

JAEA-Technology 2011-031, 123 Pages, 2012/01

JAEA-Technology-2011-031.pdf:16.08MB

The number of research reactors in the world is decreasing because of their aging. However, the planning to introduce the nuclear power plants is increasing in Asian countries. In these Asian countries, the key issue is the human resource development for operation and management of nuclear power plants after constructed them, and also the necessity of research reactor, which is used for lifetime extension of LWRs, progress of the science and technology, expansion of industry use, human resources training and so on, is increasing. From above backgrounds, the Neutron Irradiation and Testing Reactor Center began to discuss basic concept of a multipurpose low-power research reactor for education and training, etc. This design study is expected to contribute not only to design tool improvement and human resources development in the Neutron Irradiation and Testing Reactor Center but also to maintain and upgrade the technology on research reactors in nuclear power-related companies. This report treats the activities of the working group from July 2010 to June 2011 on the multipurpose low-power research reactor in the Neutron Irradiation and Testing Reactor Center and nuclear power-related companies.

Monte Carlo simulation of radial distribution of DNA strand breaks along the C and Ne ion paths

Watanabe, Ritsuko; Wada, Seiichi*; Funayama, Tomoo; Kobayashi, Yasuhiko; Saito, Kimiaki; Furusawa, Yoshiya*

Radiation Protection Dosimetry, 143(2-4), p.186 - 190, 2011/02

https://doi.org/10.1093/rpd/ncq539

Microscopic energy deposition pattern in an ion track is thought to affect on the spatial distribution of DNA damage as well as the damage spectrum. In this study, we focus on the intra-track spatial distribution of DNA damage in cellular condition based on the energy deposition pattern for each ion obtained by the detailed Monte Carlo track structure simulation. The estimation was performed for C and Ne ions with similar LET around 440 keV/m. As a result, radial DNA damage distribution shows different pattern for C and Ne ions. That is, DSBs or non-DSB type clustered damage are formed in the limited central area while the isolated damages as SSBs and base lesions are spread in larger area. Such tendency is more clearly shown for Ne ions than C ions. This result shows good agreement with the previously obtained experimental observation at TIARA, which indicates the different types of DNA damage shows different distribution pattern around C and Ne projectiles in cell nuclei.

Kinetic analysis of double-strand break rejoining reveals the DNA reparability of -irradiated tobacco cultured cells

Yokota, Yuichiro; Wada, Seiichi*; Hase, Yoshihiro; Funayama, Tomoo; Kobayashi, Yasuhiko; Narumi, Issei; Tanaka, Atsushi

Journal of Radiation Research, 50(2), p.171 - 175, 2009/04

https://doi.org/10.1269/jrr.08064

The rejoining efficiency of double-strand breaks (DSBs) was quantified in tobacco protoplasts and CHO-K1 cells following -ray irradiation in order to compare DNA reparability of higher plants with mammals. The DSB rejoining kinetics of tobacco protoplasts were well represented by a biphasic-exponential equation: half of initial-induced DSBs were rejoined for 1 h and the others were almost rejoined within 4 h. We found that the DSB rejoining kinetics of tobacco protoplasts at 27C are the same as those of CHO-K1 cells at 37C. These findings indicate that the DSB rejoining efficiency of tobacco protoplasts and CHO-K1 cells are comparable at their respective cell cultivation temperatures, suggesting that DSB rejoining efficiency is little responsible for the higher radiation-tolerance of tobacco protoplasts.

Establishment of a rearing system of the extremotolerant tardigrade ; A New model animal for astrobiology

Horikawa, Daiki*; Kunieda, Takekazu*; Abe, Wataru*; Watanabe, Masahiko*; Nakahara, Yuichi*; Yukuhiro, Fumiko*; Sakashita, Tetsuya; Hamada, Nobuyuki*; Wada, Seiichi*; Funayama, Tomoo; et al.

Astrobiology, 8(3), p.549 - 556, 2008/06

https://doi.org/10.1089/ast.2007.0139

We report the successful rearing of the herbivorous tardigrade, , by supplying the green alga as food. The life span was 35 d, deposited eggs required 5.7 d to hatch, and animals began to deposit eggs 9 d after hatching. The reared individuals of this species had an anhydrobiotic capacity throughout their life cycle in egg, juvenile, and adult stages. Furthermore, the reared adults in an anhydrobiotic state were tolerant of temperatures of 90C and -196C and exposure to 99.8% acetonitrile or irradiation with 4000 Gy He ions. Based on their life history traits and tolerance to extreme stresses, might be a suitable model for astrobiological studies of multicellular organisms.