A COBINED MINERALOGICAL AND NOBLE GAS	 STUDY OF FOUR ITOKAWAS PARTICLES: A
PROGRESS REPORT.
T. Noguchi1, R. Okazaki1, T. Mitsunari2, Y. Tobimatsu1, M.
Uesugi3, T. Yada3, Y. Karouji3, M. Kimura2, and H. Hidaka4.
1
Kyushu University. E-mail: tnoguchi@artsci.kyushu-u.ac.jp.
2
Ibaraki University. 3JAXA/ISAS, 4Hiroshima University
Introduction: Various types of surface modification textures
were found on the surface (<100 nm) of Itokawa particles [1-6].
Their textures suggest that irradiation by solar wind play an important role to form the surface modification [1,2]. On the otherhand, noble gas isotopic compositions suggest that each particle
had its individual irradiation history [7]. Therefore, we intended
to investigate the relationships between surface modification textures related to space weathering and noble gas implantation signatures. We developed a method to perform a combined study ofmineralogy and noble gas mass spectrometry for individual Itokawa particles.
Samples and Methods: We fixed four Itokawa particles on
molybdenum plates by acetone soluble glue. Three particles werefixed in a N2 filled glove box at the PMSCF/JAXA. However, weonce lost sight of one particle in a small hole on a silica glass
slide. It was attached on a Mo plate later in a clean room and carbon coated at Ibaraki University. All the samples attached on four
small Mo plates were attached on a sample holder for FIB sample
preparation. They were coated again by platinum. We observed
the surface of the particles and prepared by FIB sections fromthem by JEOL JIB-4501 FIB-SEM at Ibaraki University. The FIB
sections were further processed by low accelerating voltage Ar
milling machine Fischone NanoMill. The sections were promptly
stored in a vacuum desiccator.
After preparation of FIB sections, all the Mo plates withsamples were stored in small envelopes made by thin aluminum
foils and were rinsed by acetone in a N2 filled glove box at Ibaraki University. They were transferred to Kyushu University andnoble gas mass spectrometry were performed for all noble gas
elements using a modified VG-5400. Noble gas extraction fromeach sample was conducted stepwise at 50, 100, and 200 °C using an infrared lamp and at 300, 600 and 1400 °C using a “PotPie” mini-furnace equipped with the mass spectrometer. FIB sections were also transferred to Kyushu University in accordancewith the move of T. Noguchi from Ibaraki University to Kyushu
University.
Present state: TEM observation of the FIB sections revealed
that all the sections had been completely covered by Cu sulfide(or sulfate) small crystals after about 6 months storage in a vacuum desiccator. We are now trying to rescue the FIB sections fromthe overlying Cu sulfide crystals by using FIB-SEM carefully.
We will give a status report at the meeting.
References: [1] Noguchi et al. (2011) Science 333, 11211125. [2] Noguchi et al. (2014) Meteorit. Planet. Sci. xx, xxxxxx. [3] Matsumoto et al. (2013) 44th Lunar Planet. Sci. Conf.
abstr. #1441. [4] Thompson et al. (2014) Earth Planet. Space 66,89-99. [5] Keller and Berger (2014) , Earth Planet. Space 66, 7178. [6] Noguchi et al. (2014) Earth Planet. Space 66, 124-134. [7]Nagao et al. (2011) Science 333, 1128-1131.