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Osawa, Takahito; Kobayashi, Mikihiko*; Konno, Takeshi*; Egashira, Mitsuru*; Okazaki, Ryuji*; Miura, Yayoi*; Nagao, Keisuke*
Measurement, 50, p.229 - 235, 2014/04
Times Cited Count：1 Percentile：16.41(Engineering, Multidisciplinary)A temperature control system for a laser heating has been developed to extract noble gases from minute material samples recovered from the asteroid Itokawa by the Hayabusa spacecraft. An ultra-fine thermocouple was produced from 3% Re-W and 26% Re-W wires 25 
m in diameter, and its electromotive force was calibrated. A temperature control program was originally produced using LabVIEW 2011 in which proportional-integral-derivative (PID) control was not adopted as an algorithm of the program. The program controlled the temperature of the tiny samples appropriately. The average temperature during heating was slightly lower than the setting temperature and the standard deviation and the maximum overshoot were lower than 2.5% and 6.0% of the setting temperature, respectively. The performance of the temperature control system is high enough to conduct the stepwise heating experiment for minute extraterrestrial material samples.
He/
He ratios in natural fluidsBajo, Kenichi*; Sumino, Hirochika*; Toyoda, Michisato*; Okazaki, Ryuji*; Osawa, Takahito; Ishihara, Morio*; Katakuse, Itsuo*; Notsu, Kenji*; Igarashi, Joji*; Nagao, Keisuke*
Mass Spectrometry (Internet), 1(2), p.A0009_1 - A0009_10, 2012/11
The construction of a small-size, magnetic sector, single focusing mass spectrometer (He-MS) for the continuous, on-site monitoring of the He isotope ratio (He/He) is described. The instrument is capable of measuring He/
Ne ratios dissolved in several different types of natural fluids of geochemical interest, such as groundwater and gas from hot springs, volcanoes and gas well fields. Ion optics of the He-MS was designed by using the ion trajectory simulation program TRIO so as to measure He and He simultaneously with a double collector system under mass resolution power of 
500. Presently attained specifications of the He-MS are; (1) mass resolving power of ca. 490, enough to separate He
from interfering ions, HD and H
, (2) ultra-high vacuum condition, and (3) high sensitivity enough to detect He amount 3000000 atoms).
Nagao, Keisuke*; Okazaki, Ryuji*; Nakamura, Tomoki*; Miura, Yayoi*; Osawa, Takahito; Bajo, Kenichi*; Matsuda, Shintaro*; Ebihara, Mitsuru*; Ireland, T.*; Kitajima, Fumio*; et al.
Science, 333(6046), p.1128 - 1131, 2011/08
Times Cited Count：131 Percentile：95.12(Multidisciplinary Sciences)A steroid surface materials record regolith processes and a history of cosmic-ray irradiation. Noble gas isotopes in three rocky grains from Itokawa have been determined. High concentrations of solar He, Ne, and Ar, as high as those in lunar soils, are released at variable temperatures from each sample. The isotopic compositions are essentially identical to those of solar wind but distinguishable in He relative abundance. These noble gas characteristics can be explained by repeated implantation and preferential loss of solar He by removal of weathered He-rich rim on the grain surface through friction among regolith grains on Itokawa. Residence time of regolith materials on Itokawa is alculated to be shorter than 10 Myr, suggesting that regolith materials of small asteroids would escape easily to space.
Osawa, Takahito; Yamamoto, Yukio*; Noguchi, Takaaki*; Iose, Akari*; Nagao, Keisuke*
Meteoritics & Planetary Science, 45(8), p.1320 - 1339, 2010/08
Times Cited Count：12 Percentile：35.32(Geochemistry & Geophysics)The interior texture and chemical and noble gas composition of 99 cosmic spherules collected from the meteorite ice field around the Yamato Mountains in Antarctica were investigated. Their textures were used to classify the spherules into six different types reflecting the degree of heating. An enigmatic spherule, labeled M240410, had an extremely high concentration of cosmogenic nuclides. Assuming 4
exposure to galactic and solar cosmic rays as a micrometeoroid and no exposure on the parent body, the cosmic-ray exposure (CRE) age of 393 Myr could be computed using cosmogenic 
Ne. Under these model assumptions, the inferred age suggests that the particle might have been an Edgeworth-Kuiper Belt object. Alternatively, if exposure near the surface of its parent body was dominant, the CRE age of 382 Myr can be estimated from the cosmogenic 
Ar using the production rate of the 2 exposure geometry, and implies that the particle may have originated in the mature regolith of an asteroid.
Osawa, Takahito; Hatsukawa, Yuichi; Nagao, Keisuke*; Koizumi, Mitsuo; Oshima, Masumi; Toh, Yosuke; Kimura, Atsushi; Furutaka, Kazuyoshi
Geochemical Journal, 43(6), p.415 - 422, 2009/00
Times Cited Count：4 Percentile：16.37(Geochemistry & Geophysics)The Cretaceous-Tertiary (K-T) boundary about 65 million years ago records a mass extinction event caused by a bolide impact. K-T boundary clay collected from Stevns Klint, Denmark was investigated in this work. Iridium concentrations of eight clays across the K-T boundary were determined using a multiple 
-ray analysis system after neutron activation. Anomalously high Ir concentrations were detected in five marl samples, with the highest concentration being 29.9 ppb. Four samples were analyzed for all noble gases. No extraterrestrial Ar, Kr, and Xe were discovered in any of the samples, although most of the He which was detected was extraterrestrial. Solar-like Ne was observed only in the sample SK4, which had an Ir concentration of 14.3 ppb, indicating the presence of micrometeorites.
Osawa, Takahito; Nagao, Keisuke*
Antarctic Meteorite Research, (19), p.58 - 78, 2006/10
Polymict breccias are useful for research of solar activity because some preserve plenty of solar noble gases implanted during asteroidal formation processes. In this study, noble gas compositions of Antarctic and non-Antarctic polymict breccias were determined using laser gas-extraction and stepwise pyrolysis techniques. Of the polymict breccias measured in this work, 5 of 18 were identified as gas-rich meteorites (regolith breccias) and 4 of those 5 are H chondrites. The high population of gas-rich H chondrites compared with L and LL chondrites was presumably related to the depth of regolith formed on each parent body. It is notable that the major part of polymict breccias did not have solar noble gases. Noble gas analyses with stepwise heating method were done for 11 polymict breccias. Gas-rich meteorites have high concentrations of solar-derived He and Ne, which were released at relatively low temperature steps. Cosmogenic nuclides were comparatively dominant at high temperature steps. Five sources determined the observed Ar isotopic compositions. The components were: atmospheric, radiogenic, solar wind (SW), solar energetic particles (SEP), and cosmogenic. In contrast, Ne isotopic compositions of most regolith breccias con be explained simply by three-component mixing, such as SW, SEP, and cosmogenic. Indications of primordial trapped components were observed only in Willard (b), in which carbonaceous chondrite clasts were discovered previously. Cosmic-ray exposure ages were calculated from excess He, Ne, and Ar. Regolith breccias did not have systematically longer ages than gas-poor samples, indicating that the parent body exposure ages of the meteorites on the order of tens of millions of years at most.
Nagao, Keisuke*
JNC TY7400 2004-001, 74 Pages, 2004/05
JNC-TY7400-2004-001.pdf:3.07MB
Isotopic compositions of noble gases and Sr in groundwaters and rocks from Tono and Horonobe districts were analyzed to investigate the movement and origin of the groundwaters. At Tono, 3He/4He ratios decrease with increasing of 4He/20Ne ratios. This means that noble gases at Tono are a mixture of air and radiogenic He. In contrast, a Na-Cl type hot-spring (Takasago) and groundwater from well DH-15 at Tono and all wells from Horonobe show the different tendency. These groundwaters must be contributed by noble gas with deep origin. Sr isotope compositions of groundwater at Tono are far from those of rocks and close to those of carbonates in fractures, where the isotopic difference between groundwaters and rocks (*87Sr) decrease with increasing depth. These results indicate that Sr isotopic compositions of groundwater are controlled by carbonate dissolution/precipitation. Experimental results of Sr isotopic compositions on water-rock interaction support the view. In conclusion, noble gas and Sr isotopes are very useful tools to study water movements and to discuss their origins by combining other geochemical approaches.
Osawa, Takahito; Nagao, Keisuke*; Ono, Masao
no journal, ,
Primordial trapped noble gas component in primitive chondrites is concentrated in phase Q. We tried to separate phase Q from a carbonaceous chondrite using ultra-centrifugation. Noble gases are concentrated in a heavy fraction, showing that phase Q may be heavy carbonaceous materials or heavy particles attached to carbonaceous materials.
