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Niihara, Takafumi*; Yokoyama, Tatsunori; Arai, Tomoko*; Misawa, Keiji*
Meteoritics & Planetary Science, 56(8), p.1619 - 1625, 2021/08
Times Cited Count：1 Percentile：10.87(Geochemistry & Geophysics)We have conducted petrological and mineralogical studies on an igneous clast in the Northwest Africa (NWA) 1685 (LL4) chondrite. In an earlier description, the meteorite contained similar clasts in the LL chondritic breccias Yamato (Y)-74442 (LL4), Bhola (LL3-6), and Kraehenberg (LL5). We carefully compared their textures as well as mineral and matrix compositions with those of alkali-rich clasts in the LL chondritic breccias. Olivine grains are embedded in glassy matrix and have no chemical. Shock melt veins and fractures were observed only in olivine grains and did not continue to matrix. Major and minor element compositions of olivine grains in the clast are homogeneous. Potassium abundance of matrix glasses of the NWA 1685 clast is lower than those of alkali-rich igneous clasts in Y-74442, Bhola, and Kraehenberg, indicating that the igneous clasts in NWA 1685 are different from the alkali-rich clasts previously reported in the LL chondritic breccias and that they could have formed during an impact melting event, quenched on the LL-chondrite parent body, and finally incorporated into breccia.
Yokoyama, Tatsunori; Misawa, Keiji*; Okano, Osamu*; Minowa, Haruka*; Fukuoka, Takaaki*
Journal of Radioanalytical and Nuclear Chemistry, 310(1), p.81 - 89, 2016/10
Times Cited Count：1 Percentile：10.71(Chemistry, Analytical)The identification of alkali-rich components in extraterrestrial materials along with their separation from other constituents is indispensable for subsequent cosmochemical and isotopic studies. This paper presents a simple pre-screening method for such materials by autoradiography using imaging plates (IPs), which is applicable to identification of mm-sized samples containing ca. 30 
g of potassium in the Yamayo-74442 chondrite. The detection limit of IPs was 
1 mBq of 
K under 49 days exposure. The method provides an opportunity to screen meteorite materials non-destructively and to inexpensively check potassium-rich areas and suitable for the K-Ca and K-Ar (
Ar-Ar) age determinations.
Suzuya, Kentaro; Kameda, Yasuo*; Otomo, Toshiya*; Yoshida, Koji*; Ito, Keiji*; Fukunaga, Toshiharu*; Misawa, Masakatsu*
Journal of Neutron Research, 13(1-3), p.123 - 128, 2005/03
The design, performance, philosophy, lessons learned and advantages of the neutron total scattering spectrometer for hydrogenous materials, FAST, under consideration for the J-PARC-JSNS, are described. In particular, novel instrumentation concept such as the small fractional scattered neutron flight path, 
= L
/(L
+L), where L is the incident flight path, moderator to sample, L is the scattered neutron flight path from sample to detector, is presented and their expected performance at the JSNS is considered.
Shiroya, Seiji*; Misawa, Tsuyoshi*; Unesaki, Hironobu*; Ichihara, Chihiro*; Kobayashi, Keiji*; Nakamura, Hiroshi*; Shin, Kazuo*; Imanishi, Nobutsugu*; Kanazawa, Satoshi*; Mori, Takamasa
JAERI-Tech 2004-025, 93 Pages, 2004/03
JAERI-Tech-2004-025.pdf:6.69MB
In view of the future plan of Research Reactor Institute, Kyoto University, the present study consisted of (1) the transmission experiments of high energy neutrons through materials, (2) experimental simulation of ADSR using the Kyoto University Critical Assembly(KUCA), and (3) conceptual neutronics design study on KUR type ADSR using the MCNP-X code. Through the present study, valuable knowledge on the basic nuclear characteristics of ADSR, which is indispensable to promote the study on ADSR, was obtained both theoretically and experimentally. For the realization of ADSR, it is considered to be necessary to accumulate results of research steadily. For this purpose, it is inevitable (1) to compile the more precise nuclear data for the wide energy range, (2) to establish experimental techniques for reactor physics study on ADSR including subcriticality measurement and absolute neutron flux measurement, and (3) to develop neutronics calculation tools which take into account the neutron generation process by the spallation reaction and the delayed neutron behavior.
Yokoyama, Tatsunori; Misawa, Keiji*; Yoneda, Shigekazu*
no journal, ,
no abstracts in English
Niihara, Takafumi*; Tsuzuki, Yuki*; Misawa, Keiji*; Yokoyama, Tatsunori; Yoneda, Shigekazu*
no journal, ,
Some brecciated chondrites contain alkaline-rich igneous clasts. Their formational process is explained as early nebular condensates followed by shock melting. The Beardsley chondrite (H5) possesses large amounts of Rb compared to other H chondrites. However, detailed petrological and mineralogical signatures of Beardsley are still lacking and there is no petrological and mineralogical evidence for alteration such as presence of halite/sylvite or other alkaline-rich phases contained in other H chondrites. Here we conduct petrological and mineralogical study for the meteorite, especially to clarify secondary effect(s) and distribution of alkaline elements on the chondrites and discuss the petrogenesis of Beardsley. Petrological and mineralogical features of Beardsley are similar to those observed in impact melted H-chondrites, implying that the grey lithology is a product of impact melting event(s). On the other hand, the higher KO content in the grey lithology cannot be explained only by an impact melting process but is still unclear at this stage.
