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In the last decade, non-destructive elemental analysis using negative muon beams advanced significantly. This method can be used to determine the elemental composition of bulk materials without causing damage. In this study, we performed a negative muon irradiation experiment for a Northwest Africa 482 lunar meteorite (NWA482), which was installed in a stainless steel analysis chamber. The analysis chamber was filled with helium gas to suppress the background signals caused by air-scattering muons. The muonic X-rays from Al, Fe, Ca, Mg, Si, and O in the samples were detected using six high-purity germanium semiconductor detectors arranged around the analysis chamber. To correct the X-ray self-absorption effect of the samples, a Monte-Carlo simulation using Geant4 toolkit was used. Based on the quantitative analysis for muonic X-ray measurement with the correction application from the simulation, we successfully investigated the analytical sensitivity of each element in meteorites based on the NWA482 data.

第8回極域科学シンポジウム/個別セッション：[OA] 南極隕石12月6日（水）国語研究所 2階講堂The Eighth Symposium on Polar Science/Ordinary sessions: [OA] Antarctic meteoritesWed. 6 Dec./2F Auditorium, National Institute for Japanese Language and Linguistics

著者人数: 26名, Accepted: 2017-02-15, 資料番号: SA1160290000

The prompt gamma‐ray analysis (PGA) system installed in the Japan Research Reactor‐3 (JRR-3) was automated between 2012 and 2013. This automation is a good example of a large‐scale old analytical device automated in a nuclear facility. This automatic system has several useful functions, such as automatic sample exchange and analysis, automatic helium gas flow control and flow channel switching function, automatic neutron recording system, and fail‐safe function using Machine Vision, and the Internet. The analysis system was automated using a vertical revolute joint robot, control programs, and data acquisition devices. The main control software named AutoPGA was developed using LabVIEW and the program can control all functions of the automatic system, capable of analyzing up to 14 samples automatically. In the automation, the core of the PGA system was not modified and the extremely low background level of gamma rays was maintained well; however, the efficiency of routine measurements dramatically increased. Because the instruments used in the automatic PGA system are not unique, the basic design of the system can be easily applied to other large‐scale analytical devices.

著者人数: 26名, Accepted: 2011-08-02, 資料番号: SA1003194000

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 can 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 ^3He, ^(21)Ne, and ^(38)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.

Noble gas abundances in Antarctic cosmic spherules collected from the Tottuki Point on the Soya Coast, Antarctica, are considerably lower than those reported in unmelted micrometeorites, indicating severe heating of the cosmic spherules during atmospheric entry. Although ^3He was below detection limits (2 X 10^ cm^3 STP) in most spherules, ^3He was detectable in three spherules and their ^3He/^4He ratios were close to those of unmelted micrometeorites. Ne and Ar abundances and isotopic compositions were determined for more than half of the spherules. Thirteen samples had high ^Ne/^Ne ratios, possibly reflecting the presence of cosmogenic ^Ne, although blank corrections could not be made for most samples due to the low Ne concentrations. Eight particles had ^Ar/^Ar ratios lower than the atmospheric value of 296, and five of them also had SEP (solar energetic particles)-like Ne, confirming their extraterrestrial origin. These spherules apparently preserve extraterrestrial noble gases in their interiors in spite of severe heating. Sample To440080 has ^Ar/^Ar ratio (566.3±14.8) higher than that of terrestrial atmosphere in spite of the presence of SEP-like Ne, indicating different source material from some spherules and micrometeorites. Extraterrestrial Ne and Ar were not identified in 22 of 31 analyzed spherules, although relative noble gas abundances of fifteen spherules were similar to those of unmelted micrometeorites and clearly distinguishable from terrestrial materials such as terrestrial basalt, air, and water, reflecting their extraterrestrial origin. Since noble gas abundances in Antarctic spherules can be explained as mixtures of solar and Q-components and the contribution of adsorption air is insignificant, a majority of these Antarctic spherules represent accreted extraterrestrial material and are not volcanic products.

Isotopic compositions and concentrations of noble gases were analyses for 1E and 2E samples. Two noble gas mass spectrometry systems were used for the analyses; MS-II for total melting and stepwise heating experiments on samples weighing 8-32 mg, and MS-III for laser heating using single or several grains weighing 3-40 micro g. Our data suggest that the sample 1E has noble gases similar to those for type 6 ordinary chondrites, while noble gases in 2E resemble those of carbonaceous chondrite Allende (CV3). Based on the present results we can conclude; 1) for ordinary chondritic materials several mg of sample is enough to measure all noble gas isotopes, 2) for surface materials of asteroids which would contain large amounts of implanted solar noble gases, the analytical technique using laser heating is applicable to samples weighing several micro g or less, 3) noble gas isotopic compositions obtained by the technique of single grain analysis can separate grains of different meteoroids impacted asteroidal surface, and 4) histories of exposure to cosmic-rays as well as impact degassing for each grain can provide detailed erosion process occurring on the asteroidal surface., 資料番号: SA0200005000

Noble gas concentrations and isotopic compositions were determined on Antarctic Micrometeorites (AMMs) collected in Kuwagata Nunatak in the Yamato Meteorite Ice Field around the Yamato Mountains in 1998. Noble gas concentrations in Kuwagata AMMs are lower than those of previously measured Dome Fuji AMMs. The heavy noble gas composition is chondritic and shows no atmospheric contamination. In order to clarify the differences of noble gas concentrations between Kuwagata and Dome Fuji AMMs, statistic calculations were done. The differences in ^4He, ^Ar, ^Kr, and ^Xe concentrations between the two types of AMMs are significant in both F-test and T-test. On the other hand, ^Ar is not significant in the F-test, and ^Ne is not significant in both tests. These results revealed a systematic decrease of noble gas concentrations in Kuwagata AMMs compared to those of the Dome Fuji AMMs. Since jarosite-a by-product mineral from aqueous alteration of sulfide minerals-was detected in Kuwagata samples, He loss may be due to aqueous alteration in Antarctic glacial ice. A contamination by atmospheric noble gases might be avoided by sample preparation using acetone to detach AMMs from stainless steal filters.

Mid-infrared absorption spectra were obtained for 6 carbonaceous chondrites and 6 Antarctic micrometeorites (AMMs) with transmission light using an IR microscope. Obvious absorption bands caused by O-H stretching vibration at 3400cm^ and H-O-H bending vibration at 1640cm^ were detected for CI, CM2,CR2,and CO3 chondrites. All the chondrite samples had Si-O stretching band at around 1000cm^. Allende (CV3) exhibited only Si-O stretching band at near 900cm^ and no O-H bands. Infrared absorption spectra for AMMs showed no O-H stretching vibration reflecting their dry condition, except for F97AC019 and F97AC017 with weak O-H stretching band. Heating experiments on the grains of Murchison and Orgueil with sizes as small as AMMs (∿100μm) were carried out in order to clarify the dehydration effect of micrometeorite during the atmospheric entry. Heating times were 30 and 60s at temperatures every 100℃ from 500℃ to 1000℃. At relatively lower temperature condition (≤700℃), water in carbonaceous chondrites was not depleted. O-H stretching vibration at 3400cm^ was, however, vanished at higher temperature (≥800℃). This might show that AMMs were heated to 800℃ or more during atmospheric entry if our hearting duration is reasonable. Noble gas measurement using laser heating was performed for individual AMMs after the infrared microscopic analyses. Solar-He was detected for 4 samples. F97AC019 with very high concentration of helium (8.1×10^cm^3 STP/g) preserve solar-Ne and primordial trapped argon component. We have discovered an extraordinary AMM, F97AC021,with highly concentrated organic matters. Intense C-H stretching vibration at 2900cm^ and complex absorption pattern appeared in the range from 1400cm^ to 1800cm^ were detected. The AMM might have a potential to have plenty of extraterrestrial organic compounds.

All noble gases in 12 individual Antarctic micrometeorites, series F96C and F96D, taken from a water tank at the Dome Fuji Station, were measured by using Nd-YAG CW laser-extraction system. According to the results of light noble gases, the micrometeorites can be separated into two groups, "gas-rich" and "gas-poor". Samples in the gas-rich group have SEP-like ^3He/^4He ratios and Ne isotopic ratios between SEP- and Solar wind-Ne, which are consistent with previous reports on micrometeorites or IDPs. On the other hand, samples in the gas-poor group have very low ^3He/^4He ratios and ^Ne/^Ne ratios lower than the atmospheric values. The ^Ar/^Ar ratios are also separated into two groups, i. e., samples with lower ^Ar/^Ar belong to the gas-rich group. Cosmogenic noble gases were undetected in all the samples and cosmic-ray exposure ages may be shorter than 4.5Ma considering error limits of Ne data. Heavy noble gas elemental compositions are chondritic. There was no correlation between the concentration of volatile elements, sulfur, and that of He and Ne.

Solar Wind Noble Gases in Micrometeorites

第32回太陽系科学シンポジウム (2010年12月20-21日. 宇宙航空研究開発機構宇宙科学研究所), 相模原市, 神奈川県, 32nd Solar System Exploration Symposium (December 20-21, 2010. Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency(JAXA)(ISAS)), Sagamihara, Kanagawa Japan, 形態: カラー図版あり, 形態: CD-ROM1枚, 著者人数: 34人, Physical characteristics: Original contains color illustrations, Note: One CD-ROM, Number of authors: 34, 資料番号: AA0065421011