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.

Development of a water purifier for radioactive cesium removal from contaminated natural water by radiation-induced graft polymerization

Seko, Noriaki*; Hoshina, Hiroyuki*; Kasai, Noboru*; Shibata, Takuya; Saiki, Seiichi*; Ueki, Yuji*

Radiation Physics and Chemistry, 143, p.33 - 37, 2018/02

https://doi.org/10.1016/j.radphyschem.2017.09.007

Evaluation of a cesium adsorbent grafted with ammonium 12-molybdophosphate

Shibata, Takuya; Seko, Noriaki; Amada, Haruyo; Kasai, Noboru; Saiki, Seiichi; Hoshina, Hiroyuki; Ueki, Yuji

Radiation Physics and Chemistry, 119, p.247 - 252, 2016/02

https://doi.org/10.1016/j.radphyschem.2015.10.026

Development of an adsorbent for Cs removal synthesized by radiation-induced graft polymerization

Shibata, Takuya; Seko, Noriaki; Amada, Haruyo; Kasai, Noboru; Saiki, Seiichi; Hoshina, Hiroyuki; Ueki, Yuji

Nihon Ion Kokan Gakkai-Shi, 26(1), p.9 - 14, 2015/01

https://doi.org/10.5182/jaie.26.9

Adsorption properties of styrenesulfonate-grafted fibrous metal adsorbent

Ueki, Yuji; Saiki, Seiichi; Seko, Noriaki

Nihon Ion Kokan Gakkai-Shi, 25(4), p.99 - 104, 2014/11

https://doi.org/10.5182/jaie.25.99

Optimization of grafted fibrous polymer as a solid basic catalyst for biodiesel fuel production

Ueki, Yuji; Saiki, Seiichi; Shibata, Takuya; Hoshina, Hiroyuki; Kasai, Noboru; Seko, Noriaki

International Journal of Organic Chemistry, 4(2), p.91 - 105, 2014/06

https://doi.org/10.4236/ijoc.2014.42011

Grafted fibrous polymer with quaternary amine groups could function as a highly-efficient catalyst for biodiesel fuel (BDF) production. In this study, the optimization of grafted fibrous polymer (catalyst) and transesterification conditions for the effective BDF production was attempted through a batch-wise transesterification of triglyceride (TG) with ethanol (EtOH) in the presence of a cosolvent. Trimethylamine was the optimal quaternary amine group for the grafted fibrous catalyst. The optimal degree of grafting of the grafted fibrous catalyst was 170%. The optimal transesterification conditions were as follows: The molar quantity of quaternary amine groups, transesterification temperature, molar ratio of TG and EtOH, and primary alkyl alcohol were 0.8 mmol, 80C, 1:200, and 1-pentanol, respectively. The grafted fibrous catalyst could be applied to BDF production using natural oils. Furthermore, the grafted fibrous catalyst could be used repeatedly after regeneration involving three sequential processes, i.e., organic acid, alkali, and alcohol treatments, without any significant loss of catalytic activity.

Pilot-scale synthesis for radioactive cesium adsorbents by radiation graft polymerization and their field tests

Kasai, Noboru; Iwanade, Akio; Ueki, Yuji; Saiki, Seiichi; Hoshina, Hiroyuki; Seko, Noriaki

JAEA-Technology 2013-046, 25 Pages, 2014/02

JAEA-Technology-2013-046.pdf:9.63MB

To remove their radioactive species which have long radioactive half-life from the circumstances as rapidly as possible, we developed novel radioactive cesium adsorbents containing ammonium 12-molybdophosphate, which had adsorption selectivity for cesium ion, by radiation grafting method. The bench-scale equipment 150 times as large volume as laboratory scale was established for graft polymerization. The radioactive cesium adsorbents 1,000 times as large as laboratory scale were successfully synthesized with the bench-scale equipment. Moreover, the adsorption performance with radioactive cesium in environmental water was evaluated at field tests in Fukushima Prefecture. As a result, the adsorbents could successfully remove radioactive cesium dissolved in environmental water below the detection limit of radioactivity concentration.

Positron lifetimes and mechanical properties of -irradiated ultra high molecular weight polyethylene

Kobayashi, Yoshinori*; Yamawaki, Masato*; Oka, Toshitaka; Saiki, Seiichi; Mohamed, H.*; Hattori, Kanehisa*; Watanabe, Yoshihiro*

Materials Science Forum, 733, p.147 - 150, 2013/00

https://doi.org/10.4028/www.scientific.net/MSF.733.147

Positron annihilation lifetime spectroscopy (PALS) has widely been used for probing open volume defects in various materials. PALS is in principle non-destructive, yet conventional PALS is not strictly non-destructive because cutting out of two specimens from the material is required. Recently we developed a novel method of PALS, which is potentially applicable to non-destructive, onsite material inspection. In order to explore the possibility of onsite monitoring of polymer degradation by this novel method of PALS, we studied variations of positron lifetime and mechanical properties of ultra high molecular weight polyethylene (UHMWPE) subjected to -irradiation. Correlations were found between the mechanical properties and o-Ps lifetimes, suggesting the feasibility of non-destructive, onsite monitoring of polymer degradation by PALS. The effect of -irradiation on positronium formation is discussed.

Radiation-induced grafting of acrylonitrile monomer onto cellulose nonwoven fabric

Saiki, Seiichi; Puspitasari, T.*; Seko, Noriaki

JAEA-Review 2011-043, JAEA Takasaki Annual Report 2010, P. 44, 2012/01

https://jopss.jaea.go.jp/pdfdata/JAEA-Review-2011-043.pdf

no abstracts in English

NMR analysis of fractionated irradiated -carrageenan oligomers as plant growth promoter

Abad, L.*; Saiki, Seiichi; Nagasawa, Naotsugu; Kudo, Hisaaki*; Katsumura, Yosuke*; Dela Rosa, A. M.*

Radiation Physics and Chemistry, 80(9), p.977 - 982, 2011/09

https://doi.org/10.1016/j.radphyschem.2011.04.006

The optimum molecular weight of irradiated -carrageenan for the plant growth promoting effect is known to be around 10 kDa, which is obtained by irradiation at doses of 100 kGy in solid and of 2 kGy in 1% aqueous solution. In this study, isolated fraction by membrane filter of irradiated -carrageenan was analyzed by NMR. The chemical shifts of C and H spectra at the range of 3-10 kDa indicated that the basic functional structure of -carrageenan (alternating D-galactose-4-sulfate and 3,6-anhydro-D-galactose dimer) remains intact. No radiolytic product having carbonyl groups was detected at the range of 3-10 kDa, and moved to less than 3 kDa probably. From these results, it is assumed that the plant growth promoting effect of irradiated -carrageenan depends on the molecular weight, its intact structure, and not on the radiolytic products.