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Journal Articles

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

 Times Cited Count:30 Percentile:96.52(Astronomy & Astrophysics)

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 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$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.

Journal Articles

The Surface composition of asteroid 162173 Ryugu from Hayabusa2 near-infrared spectroscopy

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Arai, Takehiko*; Nakauchi, Yusuke*; Nakamura, Tomoki*; Matsuoka, Moe*; et al.

Science, 364(6437), p.272 - 275, 2019/04

 Times Cited Count:233 Percentile:99.74(Multidisciplinary Sciences)

The near-Earth asteroid 162173 Ryugu, the target of Hayabusa2 sample return mission, is believed to be a primitive carbonaceous object. The Near Infrared Spectrometer (NIRS3) on Hayabusa2 acquired reflectance spectra of Ryugu's surface to provide direct measurements of the surface composition and geological context for the returned samples. A weak, narrow absorption feature centered at 2.72 micron was detected across the entire observed surface, indicating that hydroxyl (OH)-bearing minerals are ubiquitous there. The intensity of the OH feature and low albedo are similar to thermally- and/or shock-metamorphosed carbonaceous chondrite meteorites. There are few variations in the OH-band position, consistent with Ryugu being a compositionally homogeneous rubble-pile object generated from impact fragments of an undifferentiated aqueously altered parent body.

Journal Articles

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

 Times Cited Count:15 Percentile:86.05(Chemistry, Physical)

Journal Articles

ESR dosimetric study on $$gamma$$-ray irradiation induced radicals in binder materials of alanine dosimeter components

Seito, Hajime; Saiki, Seiichi; Kobinata, Kishio*; Kojimja, Takuji*

JAEA-Review 2015-022, JAEA Takasaki Annual Report 2014, P. 147, 2016/02

Journal Articles

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

 Times Cited Count:11 Percentile:73.73(Chemistry, Physical)

Journal Articles

Development of grafted adsorbents for Cs removal from natural water source

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

Hoshasen To Sangyo, (138), p.9 - 12, 2015/06

no abstracts in English

Journal Articles

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

Journal Articles

The Volume reduction method of radioactively-contaminated plant waste through extraction and removal of radioactive cesium

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

Nihon Ion Kokan Gakkai-Shi, 25(4), p.170 - 175, 2014/11

Journal Articles

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

Journal Articles

Synthesis of highly-selective fibrous adsorbent by introducing 2-ethylhexyl hydrogen-2-ethylhexylphosphonate for scandium adsorption

Hoshina, Hiroyuki; Ueki, Yuji; Saiki, Seiichi; Seko, Noriaki

International Journal of Organic Chemistry, 4(3), p.195 - 200, 2014/09

Journal Articles

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

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, 80$$^{circ}$$C, 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.

Journal Articles

Effect of initial radical concentration on radiation-induced graft polymerization on polyethylene nonwoven fabric

Saiki, Seiichi; Okaya, Keiko*; Seko, Noriaki

JAEA-Review 2013-059, JAEA Takasaki Annual Report 2012, P. 54, 2014/03

no abstracts in English

JAEA Reports

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


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.

Journal Articles

A Novel avenue to gold nanostructured microtubes using functionalized fiber as the ligand, the reductant, and the template

Ma, H.*; Chi, H.*; Wu, J.*; Wang, M.*; Li, J.*; Hoshina, Hiroyuki; Saiki, Seiichi; Seko, Noriaki

ACS Applied Materials & Interfaces, 5(17), p.8761 - 8765, 2013/09

 Times Cited Count:14 Percentile:44.16(Nanoscience & Nanotechnology)

Journal Articles

Positron lifetimes and mechanical properties of $$gamma$$-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

 Times Cited Count:3 Percentile:81.87

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 $$gamma$$-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 $$gamma$$-irradiation on positronium formation is discussed.

Journal Articles

Hybrid grafted ion exchanger for decontamination of radioactive cesium in Fukushima Prefecture and other contaminated areas

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

Journal of Radioanalytical and Nuclear Chemistry, 293(2), p.703 - 709, 2012/08

 Times Cited Count:33 Percentile:91.52(Chemistry, Analytical)

We have developed a material that can be used to remove cesium (Cs) in Fukushima Prefecture and other contaminated areas. The developed material was prepared by radiation-induced graft polymerization of ammonium 12-molybdophosphate (AMP) and acrylonitrile (AN) onto nonwoven polyethylene fabric. In the batch study, the adsorbent was able to remove 90%, 87% and 64% of Cs from pure water, acidic water and seawater, respectively. In the column study, adsorbent packed in a column with a diameter of 7 mm and a height of 5 cm was able to remove nearly the entire amount of dissolved Cs. The solution (1 ppm Cs at pH 7) was pumped into the column at a space velocity of 300 h$$^{-1}$$, in which the Cs adsorption capacity at the breakthrough point reached 54 g-Cs/kg-adsorbent. Adsorbent packed into a cartridge with a diameter of 4 cm and a height of 3.8 cm was used in a field test on removing dissolved radioactive Cs in Iitate-mura, and this test was conducted successfully.

Journal Articles

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

no abstracts in English

Journal Articles

Spin-trapping reactions of a novel gauchetype radical trapper G-CYPMPO

Oka, Toshitaka; Yamashita, Shinichi; Midorikawa, Masamichi*; Saiki, Seiichi; Muroya, Yusa*; Kamibayashi, Masato*; Yamashita, Masayuki*; Anzai, Kazunori*; Katsumura, Yosuke*

Analytical Chemistry, 83(24), p.9600 - 9604, 2011/10

 Times Cited Count:38 Percentile:77.45(Chemistry, Analytical)

Chemical reactions of a novel gauche-type spin trap, G-CYPMPO ($textit{sc}$-5-(5,5-dimethyl-2-oxo-1,3,2-dioxaphosphinan-2-yl)-5-methy-1-pyrroline 1-oxide, torsion angle: O1-P1-C6-N1 of 52.8$$^{circ}$$), with reactive oxygen species were examined by pulse radiolysis technique with 35 MeV electron beam and electron spin resonance spectroscopy after $$^{60}$$Co $$gamma$$-ray irradiation. The spin trapping reaction rate constants of G-CYPMPO toward hydroxyl radical and hydrated electron were estimated to be (4.2$$pm$$0.1)$$times$$10$$^{9}$$ and (11.8$$pm$$0.2)$$times$$10$$^{9}$$ M$$^{-1}$$s$$^{-1}$$, respectively. Half-lives of spin adducts, hydroxyl radical and perhydroxyl radical adducted G-CYPMPO were estimated to be $$sim$$35 and $$sim$$90 min, respectively. A comparison of the results with earlier reports using different radical sources suggests that the purity of the solution and/or the radical generation technique may influence the stability of spin adducts.

Journal Articles

NMR analysis of fractionated irradiated $$kappa$$-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

 Times Cited Count:14 Percentile:72.96(Chemistry, Physical)

The optimum molecular weight of irradiated $$kappa$$-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 $$kappa$$-carrageenan was analyzed by NMR. The chemical shifts of $$^{13}$$C and $$^{1}$$H spectra at the range of 3-10 kDa indicated that the basic functional structure of $$kappa$$-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 $$kappa$$-carrageenan depends on the molecular weight, its intact structure, and not on the radiolytic products.

Journal Articles

Radiation-induced grafting of acrylonitrile monomer onto cellulose nonwoven fabric

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

Proceedings of 12th International Conference on Radiation Curing in Asia (RadTech Asia 2011) (Internet), p.124 - 125, 2011/06

87 (Records 1-20 displayed on this page)