Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Ryuji Okazaki Last modified date:2019.11.29

Associate Professor / Material Science of Solar Planets / Department of Earth and Planetary Sciences / Faculty of Sciences

1. Yuichiro Cho, Shingo Kameda, Mamoru Okuno, Misa Horiuchi, Kazuo Shibasaki, Ryo Wagatsuma, Yusuke Aida, Yayoi N. Miura, Kazuo Yoshioka, Ryuji Okazaki, Seiji Sugita, Experimental characterization of elastomeric O-rings as reusable seals for mass spectrometric measurements
Application to in situ K–Ar dating on Mars, Advances in Space Research, 10.1016/j.asr.2017.07.002, 60, 7, 1453-1462, 2017.10, Mass spectrometry has been widely used in lander missions to characterize the volatiles in rocks and soils on planetary surfaces. A good vacuum seal is very important for introducing such solid samples to a vacuum chamber and ejecting them. However, multiple measurements require many metal gaskets, leading to extra weight and complexity for the instruments. In this study, we investigate the capability of three kinds of elastomeric O-rings (Viton, Nexus-SLT, and Nexus-FV) as vacuum seals for mass spectrometric measurements, particularly for in situ K–Ar dating on Mars. First, thermal cycle tests revealed that low-temperature-resistant O-rings can maintain pressure <10−5 Pa at −60 °C under 1 bar ambient pressure, whereas Viton O-rings leaked at −25 °C. Then, the amount of 40Ar due to outgassing from the O-rings and permeation under the ambient pressure of 650 Pa or 3 Pa was measured and compared with the amounts of 40Ar that a flight-equivalent laser would liberate from potential target Martian rocks. The measured amounts were <1% of that a target rock with 5000 ppm K2O and an age of 4.2 Ga would yield. These results suggest that a Viton O-ring can maintain the Ar blank low under the Mars atmospheric pressure when temperatures are higher than −25 °C. A double O-ring seal using the low-temperature-resistant elastomers would be an alternative approach at lower temperatures. The elastomeric O-rings would be useful for constructing a small and light-weighted mass spectrometric instrument for in situ K–Ar dating on Mars..
2. Hikaru Yabuta, Takaaki Noguchi, Shoichi Itoh, Tomoki Nakamura, Akira Miyake, Shinichi Tsujimoto, Noriaki Ohashi, Naoya Sakamoto, Minako Hashiguchi, Ken ichi Abe, Aya Okubo, A. L.David Kilcoyne, Shogo Tachibana, Ryuji Okazaki, Kentaro Terada, Mitsuru Ebihara, Hiroko Nagahara, Formation of an ultracarbonaceous Antarctic micrometeorite through minimal aqueous alteration in a small porous icy body, Geochmica et Cosmochimica Acta, 10.1016/j.gca.2017.06.047, 214, 172-190, 2017.10, A comprehensive study of the organic chemistry and mineralogy of an ultracarbonaceous micrometeorite (UCAMM D05IB80) collected from near the Dome Fuji Station, Antarctica, was carried out to understand the genetic relationship among organic materials, silicates, and water. The micrometeorite is composed of a dense aggregate of ∼5 µm-sized hollow ellipsoidal organic material containing submicrometer-sized phases such as glass with embedded metal and sulfides (GEMS) and mineral grains. There is a wide area of organic material (∼15 × 15 μm) in its interior. Low-Ca pyroxene is much more abundant than olivine and shows various Mg/(Mg + Fe) ratios ranging from ∼1.0 to 0.78, which is common to previous works on UCAMMs. By contrast, GEMS grains in this UCAMM have unusual chemical compositions. They are depleted in both Mg and S, which suggests that these elements were leached out from the GEMS grains during very weak aqueous alteration, without the formation of phyllosilicates. The organic materials have two textures—smooth and globular with an irregular outline—and these are composed of imine, nitrile and/or aromatic nitrogen heterocycles, and amide. The ratio of nitrogen to carbon (N/C) in the smooth region of the organics is ∼0.15, which is five times higher than that of insoluble organic macromolecules in types 1 and 2 carbonaceous chondritic meteorites. In addition, the UCAMM organic materials are soluble in epoxy and are thus hydrophilic; this polar nature indicates that they are very primitive. The surface of the material is coated with an inorganic layer, a few nanometers thick, that consists of C, O, Si, S, and Fe. Sulfur is also contained in the interior, implying the presence of organosulfur moieties. There are no isotopic anomalies of D, 13C, or 15N in the organic material. Interstellar photochemistry alone would not be sufficient to explain the N/C ratio of the UCAMM organics; therefore, we suggest that a very small amount of fluid on a comet must have been necessary for the formation of the UCAMM. The GEMS grains depleted in Mg and S in the UCAMM prove a very weak degree of aqueous alteration; weaker than that of carbonaceous chondrites. Short-duration weak alteration probably caused by planetesimal shock locally melted cometary ice grains and released water that dissolved the organics; the fluid would likely have not mobilized because of the very low thermal conductivity of the porous icy body. This event allowed the formation of the large organic puddle of the UCAMM, as well as organic matter sulfurization, formation of thin membrane-like layers of minerals, and deformation of organic nanoglobules..
3. Ryuji Okazaki, Hirotaka Sawada, Shinji Yamanouchi, Shogo Tachibana, Yayoi N. Miura, Kanako Sakamoto, Yoshinori Takano, Masanao Abe, Shoichi Itoh, Keita Yamada, Hikaru Yabuta, Chisato Okamoto, Hajime Yano, Takaaki Noguchi, Tomoki Nakamura, Keisuke Nagao,, Hayabusa2 Sample Catcher and Container
Metal-Seal System for Vacuum Encapsulation of Returned Samples with Volatiles and Organic Compounds Recovered from C-Type Asteroid Ryugu, Space Science Reviews, 10.1007/s11214-016-0289-5, 208, 1-4, 107-124, 2017.07, The spacecraft Hayabusa2 was launched on December 3, 2014, to collect and return samples from a C-type asteroid, 162173 Ryugu (provisional designation, 1999 JU3). It is expected that the samples collected contain organic matter and water-bearing minerals and have key information to elucidate the origin and history of the Solar System and the evolution of bio-related organics prior to delivery to the early Earth. In order to obtain samples with volatile species without terrestrial contamination, based on lessons learned from the Hayabusa mission, the sample catcher and container of Hayabusa2 were refined from those used in Hayabusa. The improvements include (1) a mirror finish of the inner wall surface of the sample catcher and the container, (2) adoption of an aluminum metal sealing system, and (3) addition of a gas-sampling interface for gas collection and evacuation. The former two improvements were made to limit contamination of the samples by terrestrial atmosphere below 1 Pa after the container is sealed. The gas-sampling interface will be used to promptly collect volatile species released from the samples in the sample container after sealing of the container. These improvements maintain the value of the returned samples..
4. Hirotaka Sawada, Ryuji Okazaki, Shogo Tachibana, Kanako Sakamoto, Yoshinori Takano, Chisato Okamoto, Hajime Yano, Yayoi Miura, Masanao Abe, Sunao Hasegawa, Takaaki Noguchi,, Hayabusa2 Sampler
Collection of Asteroidal Surface Material, Space Science Reviews, 10.1007/s11214-017-0338-8, 208, 1-4, 81-106, 2017.07, Japan Aerospace Exploration Agency (JAXA) launched the asteroid exploration probe “Hayabusa2” in December 3rd, 2014, following the 1st Hayabusa mission. With technological and scientific improvements from the Hayabusa probe, we plan to visit the C-type asteroid 162137 Ryugu (1999 JU3), and to sample surface materials of the C-type asteroid that is likely to be different from the S-type asteroid Itokawa and contain more pristine materials, including organic matter and/or hydrated minerals, than S-type asteroids. We developed the Hayabusa2 sampler to collect a minimum of 100 mg of surface samples including several mm-sized particles at three surface locations without any severe terrestrial contamination. The basic configuration of the sampler design is mainly as same as the 1st Hayabusa (Yano et al. in Science, 312(5778):1350–1353, 2006), with several minor but important modifications based on lessons learned from the Hayabusa to fulfill the scientific requirements and to raise the scientific value of the returned samples. In this paper, we will report the details of the sampling system of Hayabusa2 with results of performance tests during the development and the current status of the sampling system..
5. Takaaki Noguchi, H. Yabuta, S. Itoh, N. Sakamoto, T. Mitsunari, A. Okubo, Ryuji Okazaki, T. Nakamura, S. Tachibana, K. Terada, M. Ebihara, N. Imae, M. Kimura, H. Nagahara, Variation of mineralogy and organic material during the early stages of aqueous activity recorded in Antarctic micrometeorites, Geochmica et Cosmochimica Acta, 10.1016/j.gca.2017.03.034, 208, 119-144, 2017.07, Micrometeorites (MMs) recovered from surface snow near the Dome Fuji Station, Antarctica are almost free from terrestrial weathering and contain very primitive materials, and are suitable for investigation of the evolution and interaction of inorganic and organic materials in the early solar system. We carried out a comprehensive study on seven porous and fluffy MMs [four Chondritic porous (CP) MMs and three fluffy fine-grained (Fluffy Fg) MMs] and one fine-grained type 1 (Fg C1) MM for comparison with scanning electron microscope, transmission electron microscope, X-ray absorption near-edge structure analysis, and secondary ion mass spectrometer. They show a variety of early aqueous activities. Four out of the seven CP MMs contain glass with embedded metal and sulfide (GEMS) and enstatite whiskers/platelets and do not have hydrated minerals. Despite the same mineralogy, organic chemistry of the CP MMs shows diversity. Two of them contain considerable amounts of organic materials with high carboxyl functionality, and one of them contains nitrile (CN) and/or nitrogen heterocyclic groups with D and 15N enrichments, suggesting formation in the molecular cloud or a very low temperature region of the outer solar system. Another two CP MMs are poorer in organic materials than the above-mentioned MMs. Organic material in one of them is richer in aromatic C than the CP MMs mentioned above, being indistinguishable from those of hydrated carbonaceous chondrites. In addition, bulk chemical compositions of GEMS in the latter organic poor CP MMs are more homogeneous and have higher Fe/(Si + Mg + Fe) ratios than those of GEMS in the former organic-rich CP MMs. Functional group of the organic materials and amorphous silicate in GEMS in the organic-poor CP MMs may have transformed in the earliest stage of aqueous alteration, which did not form hydrated minerals. Three Fluffy Fg MMs contain abundant phyllosilicates, showing a clear evidence of aqueous alteration. Phyllosilicates in thee MMs are richer in Fe than those in hydrated IDPs, typical fine-grained hydrated (Fg C1) MMs, and hydrated carbonaceous chondrites. One of the Fluffy Fg MMs contains amorphous silicate, which is richer in Fe than GEMS and contains little or no nanophase Fe metal but contains Fe sulfide. Because the chemical compositions of the amorphous silicate are within the compositional field of GEMS in CP IDPs, the amorphous silicate may be alteration products of GEMS. The entire compositional field of GEMS in the CP MMs and the amorphous silicate in the Fluffy Fg MM matches that of the previously reported total compositional range of GEMS in IDPs. One Fluffy Fg MM contains Mg-rich phyllosilicate along with Fe-rich phyllosilicate and Mg-Fe carbonate. Mg-rich phyllosilicate and Mg-Fe carbonate may have been formed through the reaction of Fe-rich phyllosilicate, Mg-rich olivine and pyroxene, and water with C-bearing chemical species. These data indicate that CP MMs and Fluffy Fg MMs recovered from Antarctic surface snow contain materials that throw a light on the earliest stages of aqueous alteration on very primitive solar system bodies. Because mineralogy and isotopic and structural features of organic materials in D10IB009 are comparable with isotopically primitive IDPs, its parent body could be comets or icy asteroids showing mass ejection (active asteroids). By contrast, organic-poor CP MMs may have experienced the earliest stage of aqueous alteration and Fluffy Fg MMs experienced weak aqueous alteration. The precursor materials of the parent bodies of Fluffy Fg MMs probably contained abundant GEMS or GEMS-like materials like CP IDPs, which is common to fine-grained matrices of very primitive carbonaceous chondrites such as CR3s. However, highly porous nature of organic-poor CP MMs and Fluffy Fg MMs suggests that parent bodies of these MMs must have been much more porous than the parent bodies of primitive carbonaceous chondrites. Given no phyllosilicate among the returned samples of 81P/Wild 2 comet, the MMs may have been derived from porous icy asteroids such as active asteroids as well as P- and D-type asteroids rather than comets..
6. Ryuji Okazaki, Keisuke Nagao, Primordial and cosmogenic noble gases in the Sutter's Mill CM chondrite, Meteoritics and Planetary Science, 10.1111/maps.12819, 52, 4, 669-689, 2017.04, The Sutter's Mill (SM) CM chondrite fell in California in 2012. The CM chondrite group is one of the most primitive, consisting of unequilibrated minerals, but some of them have experienced complex processes occurring on their parent body, such as aqueous alteration, thermal metamorphism, brecciation, and solar wind implantation. We have determined noble gas concentrations and isotopic compositions for SM samples using a stepped heating gas extraction method, in addition to mineralogical observation of the specimens. The primordial noble gas abundances, especially the P3 component trapped in presolar diamonds, confirm the classification of SM as a CM chondrite. The mineralogical features of SM indicate that it experienced mild thermal alteration after aqueous alteration. The heating temperature is estimated to be <350 °C based on the release profile of primordial 36Ar. The presence of a Ni-rich Fe-Ni metal suggests that a minor part of SM has experienced heating at >500 °C. The variation in the heating temperature of thermal alteration is consistent with the texture as a breccia. The heterogeneous distribution of solar wind noble gases is also consistent with it. The cosmic-ray exposure (CRE) age for SM is calculated to be 0.059 ± 0.023 Myr based on cosmogenic 21Ne by considering trapped noble gases as solar wind, the terrestrial atmosphere, P1 (or Q), P3, A2, and G components. The CRE age lies at the shorter end of the CRE age distribution of the CM chondrite group..
7. Yuichiro Cho, Shingo Kameda, Yayoi N. Miura, Yoshifumi Saito, Shoichiro Yokota, Satoshi Kasahara, Okazaki Ryuji, 他, Conceptual Design of an In Situ K-Ar Isochron Dating Instrument for Future Mars Rover Missions, Transaction of JSASS, Aerospace Technology Japan, in-press, 2016.12.
8. Yuichiro Cho, Seiji Sugita, Yayoi N. Miura, Ryuji Okazaki, Naoyoshi Iwata, Tomokatsu Morota, Shingo Kameda, An in-situ K-Ar isochron dating method for planetary landers using a spot-by-spot laser-ablation technique, Planetary and Space Science, 10.1016/j.pss.2016.05.004, 128, 14-29, 2016.09, Age is essential information for interpreting the geologic record on planetary surfaces. Although crater counting has been widely used to estimate the planetary surface ages, crater chronology in the inner solar system is largely built on radiometric age data from limited sites on the Moon. This has resulted in major uncertainty in planetary chronology. Because opportunities for sample-return missions are limited, in-situ geochronology measurements from one-way lander/rover missions are extremely valuable. Here we developed an in-situ isochron-based dating method using the K-Ar system, with K and Ar in a single rock sample extracted locally by laser ablation and measured using laser-induced breakdown spectroscopy (LIBS) and a quadrupole mass spectrometer (QMS), respectively. We built an experimental system combining flight-equivalent instruments and measured K-Ar ages for mineral samples with known ages (~1.8 Ga) and K contents (1-8 wt%); we achieved precision of 20% except for a mineral with low mechanical strength. Furthermore, validation measurements with two natural rocks (gneiss slabs) obtained K-Ar isochron ages and initial 40Ar consistent with known values for both cases. This result supports that our LIBS-MS approach can derive both isochron ages and contributions of non-in situ radiogenic 40Ar from natural rocks. Error assessments suggest that the absolute ages of key geologic events including the Noachian/Hesperian- and the Hesperian/Amazonian-transition can be dated with 10-20% errors for a rock containing ~1 wt% K2O, greatly reducing the uncertainty of current crater chronology models on Mars..
9. Ryuji Okazaki, Takaaki Noguchi, Shin Ichi Tsujimoto, Yu Tobimatsu, Tomoki Nakamura, Mitsuru Ebihara, Shoichi Itoh, Hiroko Nagahara, Shogo Tachibana, Kentaro Terada, Hikaru Yabuta, Mineralogy and noble gas isotopes of micrometeorites collected from Antarctic snow Planetary Science, Earth, Planets and Space, 10.1186/s40623-015-0261-8, 67, 1, 2015.12, We have investigated seven micrometeorites (MMs) from Antarctic snow collected in 2003 and 2010 by means of electron microscopy, X-ray diffraction, micro-Raman spectroscopy, transmission electron microscopy (TEM) observation, and noble-gas isotope analysis. Isotopic ratios of He and Ne indicate that the noble gases in these MMs are mostly of solar wind (SW). Based on the release patterns of SW 4He, which should reflect the degree of heating during atmospheric entry, the seven MMs were classified into three types including two least heated, three moderately heated, and two severely heated MMs. The heating degrees are well correlated to their mineralogical features determined by TEM observation. One of the least heated MMs is composed of phyllosilicates, whereas the other consists of anhydrous minerals within which solar flare tracks were observed. The two severely heated MMs show clear evidence of atmospheric heating such as partial melt of the uppermost surface layer in one and abundant patches of dendritic magnetite and Si-rich glass within an olivine grain in the other. It is noteworthy that a moderately heated MM composed of a single crystal of olivine has a 3He/4He ratio of 8.44∈×∈10-4, which is higher than the SW value of 4.64∈×∈10-4, but does not show a cosmogenic 21Ne signature such as 20Ne/21Ne/22Ne∈=∈12.83/0.0284/1. The isotopic compositions of He and Ne in this sample cannot be explained by mixing of a galactic cosmic ray (GCR)-produced component and SW gases. The high 3He/4He ratio without cosmogenic 21Ne signature likely indicates the presence of a 3He-enriched component derived from solar energetic particles..
10. T. Noguchi, M. Kimura, T. Hashimoto, M. Konno, T. Nakamura, M. E. Zolensky,, A. Tsuchiyama, T. Matsumoto, J. Matsuno, Okazaki Ryuji, M. Uesugi, Y. Karouji, T. Yada, Y. Ishibashi, K. Shirai, M. Abe, T. Okada, Sylvite and halite on particles recovered from 25143 Itokawa: A preliminary report., Meteoritics & Planetary Science, 49, 1305-1314, 2014.07.
11. M. Uesugi, 他, Okazaki Ryuji, 他, Investigation of cutting methods for small samples of Hayabusa and future sample return missions., Meteoritics & Planetary Science, 49, 7, 1186-1201, 2014.07.
12. T. Yada, A. Fujimura, M. Abe, T. Nakamura, T. Noguchi, Okazaki Ryuji, K. Nagao,, Y. Ishibashi,, K. Shirai, M. E. Zolensky, S. Sandford,, T. Okada, M. Uesugi, Y. Karouji, M. Ogawa, S. Yakame, M. Ueno, T. Mukai, M. Yoshikawa, Hayabusa-returned sample curation in the Planetary Material Sample Curation Facility of JAXA., Meteoritics & Planetary Science, 10.1111/maps.12027, 49, 2, 135-153, 2014.02.
13. T. Nakamura, 他, Okazaki Ryuji, 他, Mineral chemistry of MUSES-C Regio inferred from analysis of dust particles collected from the first- and second-touchdown sites on asteroid Itokawa., Meteoritics & Planetary Science, 49, 2, 215-227, 2014.02.
14. Takaaki Noguchi, 他, Okazaki Ryuji, 他, Space weathered rims found on the surfaces of the Itokawa dust particles., Meteoritics & Planetary Science, 49, 2, 188-214, 2014.02.
15. T. Yada, 他, Okazaki Ryuji, 他, Hayabusa-returned sample curation in the Planetary Material Sample Curation Facility of JAXA., Meteoritics & Planetary Science, 49, 2, 135-153, 2014.02.
16. Akira Shimojuku, Tomoaki Kubo, Takumi Kato, Takashi Yoshino, Masayuki Nishi, Tomoki Nakamura, Ryuji Okazaki, Yuki Kakazu, Effects of pressure and temperature on the silicon diffusivity 1 of pyrope-rich garnet, Physics of the Earth and Planetary Interiors, 226, 28-38, 2014.01.
17. T. Noguchi, M. Kimura, T. Hashimoto, M. Konno, T. Nakamura, M. E. Zolensky,, M. Tanaka, Okazaki Ryuji, A. Tsuchiyama, A. Nakato, T. Ogami, H. Ishida, R. Sagae, S. Tsujimoto, T. Matsumoto, J. Matsuno, A. Fujimura, M. Abe, T. Yada, Space weathered rims found on the surfaces of the Itokawa dust particles., Meteoritics & Planetary Science, 49, 2, 188-214, 2013.05.
18. Jenniskens P., 他, Okazaki Ryuji, 他, Radar-Enabled Recovery of the Sutter's Mill Meteorite, a Carbonaceous Chondrite Regolith Breccia, Science, 10.1126/science.1227163, 338, 6114, 1583-1587, 2012.12.
19. K. Bajo, H. Sumino, M. Toyoda, Okazaki Ryuji, T. Osawa, M. Ishihara, I. Katakuse, K. Notsu, G. Igarashi, K. Nagao, Construction of a newly designed small-size mass spectrometer for helium isotope analysis: Toward the continuous monitoring of 3He/4He ratios in natural fluids., Mass Spectrometry, 10.5702, DOI:10.5702, 2012.11.
20. H. Naraoka, H. Mita, K. Hamase, M. Mita, H. Yabuta, K. Saito, K. Fukushima , F. Kitajima, S. A. Sandford, T. Nakamura, T. Noguchi, R. Okazaki, K. Nagao, M. Ebihara, H. Yurimoto, A. Tsuchiyama, M. Abe, K. Shirai, M. Ueno, T. Yada, Y. Ishibashi, T. Okada, A. Fujimura, T. Mukai, M. Yoshikawa, J. Kawaguchi., Preliminary organic compound analysis of microparticles returned from Asteroid 25143 Itokawa by the Hayabusa mission., Geochemical Journal, 46, 61-72, 2012.04.
21. M. Ebihara, S. Sekimoto, N. Shirai, Y. Hamajima, M. Yamamoto, K. Kumagai, Y. Oura, T. R. Ireland, F. Kitajima, K. Nagao, T. Nakamura, H. Naraoka, T. Noguchi, R. Okazaki, A. Tsuchiyama, M. Uesugi, H. Yurimoto, M. E. Zolensky, M. Abe, A. Fujimura, T. Mukai, Y. Yada., Neutron activation analysis of a particle returned from asteroid Itokawa., Science, 333, 1119-1121, 2011.08.
22. K. Nagao, R. Okazaki, T. Nakamura, Y. N. Miura, T. Osawa, K. Bajo, S. Matsuda, M. Ebihara, T. R. Ireland, F. Kitajima, H. Naraoka, T. Noguchi, A. Tsuchiyama, H. Yurimoto, M. E. Zolensky, M. Uesugi, K. Shirai, M. Abe, T. Yada, Y. Ishibashi, A. Fujimura, T. Mukai, M. Ueno, T. Okada, M. Yoshikawa, J. Kawaguchi., Irradiation history of Itokawa regolith material deduced from noble gases in the Hayabusa samples., Science, 333, 1128-1131, 2011.08.
23. T. Nakamura, T. Noguchi, M. Tanaka, M. E. Zolensky, M. Kimura, A. Tsuchiyama, A. Nakato, T. Ogami, H. Ishida, M. Uesugi, T. Yada, K. Shirai, A. Fujimura, R. Okazaki, S. A. Sandford, Y. Ishibashi, M. Abe, T. Okada, M. Ueno, T. Mukai, M. Yoshikawa, J. Kawaguchi., Itokawa dust particles: A direct link between S-type asteroids and ordinary chondrites., Science, 333, 1113-1116, 2011.08.
24. T. Noguchi, T. Nakamura, M. Kimura, M. E. Zolensky, M. Tanaka, T. Hashimoto, M. Konno, A. Nakato, T. Ogami, A. Fujimura, M. Abe, T. Yada, T. Mukai, M. Ueno, T. Okada, K. Shirai, Y. Ishibashi, R. Okazaki., Incipient space weathering observed on the surface of Itokawa dust particles., Science, 333, 1121-1125, 2011.08.
25. A. Tsuchiyama, M. Uesugi, T. Matsushima, T. Michikami, T. Kadono, T. Nakamura, K. Uesugi, T. Nakano, S. A. Sandford, R. Noguchi, T. Matsumoto, J. Matsuno, T. Nagano, Y. Imai, A. Takeuchi, Y. Suzuki, T. Ogami, J. Katagiri, M. Ebihara, T. R. Ireland, F. Kitajima, K. Nagao, H. Naraoka, T. Noguchi, R. Okazaki, H. Yurimoto, M. E. Zolensky, T. Mukai, M. Abe, T. Yada, A. Fujimura, M. Yoshikawa, J. Kawaguchi., Three-dimensional structure of Hayabusa samples: Origin and evolution of Itokawa regolith., Science, 333, 1125-1128, 2011.08.
26. Shimojuku A., Kubo T., Ohtani E., Nakamura T., Okazaki R. , Effects of hydrogen and iron on the silicon diffusivity of wadsleyite., Physics of the Earth and Planetary Interiors , 183, 175-182, 2010.11.
27. Ryuji Okazaki, Nobuo Takaoka, Keisuke Nagao, Tomoki Nakamura, Noble gases in enstatite chondrites released by stepped crushing and heating, Meteoritics & Planetary Science, 10.1111/j.1945-5100.2010.01025.x, 45, 3, 339-360, 2010.03.
28. D. Nakashima, T. Nakamura, R. Okazaki, Cosmic-ray exposure age and heliocentric distance of the parent bodies of enstatite chondrites ALH 85119 and MAC 88136., Meteoritics & Planetary Science, vol. 41, 851-862, 2006.06.
29. Y. Yamamoto, R. Okazaki, T. Nakamura, Effects of experimental aqueous alteration on the abundances of argon-rich noble gases in the Ningqiang carbonaceous chondrite., Meteoritics & Planetary Science, vol. 41, 541-551, 2006.04.
30. M. Kimura, M. K. Weisberg, Y. Lin, A. Suzuki, E. Ohtani, Okazaki Ryuji, Thermal history of the enestatite chondrites from silica polymorphs., Meteoritics & Planetary Science, 40, 6, 855-868, 2005.06.
31. Ebisawa N., Sumino H., Okazaki R., Takigami Y., Hirano N., Nagao K., and Kaneoka I., Construction of I-Xe and 40Ar-39Ar dating system using a modified VG3600 mass spectrometer and the first I-Xe data obtained in Japan., J. Mass Spectrom. Soc. Jpn., vol. 52, 219-232., 2004.08.
32. Okazaki Ryuji, K. Nagao, N. Imae, H. Kojima, Noble gas signatures of Antarctic nakhlites, Yamato (Y) 000593, Y000749, and Y000802, Antarctic Meteorite Research, 16, 58-79, 2003.03.
33. Okazaki Ryuji, Tomoki Nakamura, N. Takaoka, K. Nagao, Noble gases in ureilites released by crushing, Meteoritics and Planetary Sciences, 38, 5, 767-781, 2003.05.
34. Okazaki R. and Nagao K., Noble gases of Yamato 980459 shergottite., Anatarctic Meteorite Research, vol. 17, 68-83., 2004.03.
35. Okazaki Ryuji, N. Takaoka, K. Nagao, Minoru Sekiya, Tomoki Nakamura, Noble-gas-rich chondrules in an enstatite meteorite, Nature, 10.1038/35090520, 412, 6849, 795-798, 2001.08.
36. Okazaki Ryuji, N. Takaoka, T. Nakamura, K. Nagao, Cosmic-ray exposure ages of enstatite chondrites, Antarctic Meteorite Research, 13, 153-169, 1999.03.