DEPTH PROFILING ANALYSIS OF SOLAR WINDHELIUM IMPLANTED IN A NASA GENESIS SAMPLE
AND IMPLICATIONS TO JAXA HAYABUSA SAMPLES.
H. Yurimoto1 K. Bajo1, A. Jurewicz2, D. S. Burnett3, I.
Sakaguchi4, T. Suzuki4, S. Itose5, M. Ishihara6, K. Uchino7 and K.
Nagao8. 1Department of Natural History Sciences, Isotope
Imaging Laboratory, Hokkaido University, Sapporo, Hokkaido
001-0021, Japan. E-mail: yuri@ep.sci.hokudai.ac.jp. 2Center For
Meteorite Studies, Arizona State University, Tempe, AZ 852871404, USA, 3Division of Geological and Planetary Sciences,Caltech, Pasadena, California 91125, USA, 4National Institute forMaterials Science (NIMS), Tsukuba, Ibaraki 305–0044, Japan,
5JEOL Ltd., Akishima, Tokyo 196-8558, Japan, 6Department ofPhysics, Osaka University, Toyonaka, Osaka 560-0043, Japan,
7
Graduate School of Engineering Sciences, Kyushu University,Kasuga, Fukuoka 816-8580, Japan, 8Geochemical ResearchCenter, The University of Tokyo, Bunkyo, Tokyo 113-0033,
Japan.
Introduction: A unique feature of NASA Genesis and JAXA
Hayabusa samples are exposed intact surfaces to violent spaceenvironments. A noble gas mass spectrometry has measuredimplanted noble gasses of Solar wind from these return samples[1, 2]. A TEM study demonstrates that solar wind particles wereimplanted in the surface nm-layer of Itokawa particles [3].
However, in-situ distribution of solar noble gases has not been
determined ever from natural samples. In order to reveal nanoscale distribution of solar wind noble gases in astromaterials, anovel mass spectrometer of sputtered neutral mass spectrometry(SNMS) using tunneling ionization has been developed. The
development was started from 2004 at one year after launching ofHayabusa spacecraft [4]. Recently, we have newly developed
new generation SNMS capable to detect tens ppma He from ~50
nm area on solid surface [5]. This project will be figured out how
distribute He (and other noble gases and H) in the surface layer ofGenesis and Itokawa samples with tens nm resolution. If such
distribution is clarified, we can apply atomic mechanisms in solid
established in metallic elements, such as diffusion, partitioning,etc., to conventional noble gas cosmochemistry. As a result,behavior of noble gas in minerals can be used to monitor changesof space environments in such a way as to use trace element
behavior applying to terrestrial environmental research. Here we
report the first results of depth profiling of solar wind 4He
implanted on a diamond like carbon target (DOS) of Genesis
mission.
Experimental: A SNMS instrument called LIMAS was used.
A Ga beam of 1-µm diameter with 30 keV was rastered on DOS
with 5x5 µm2. Sputtered atoms from the surface are post ionized
by a strong field generated by a femto-second laser. The ionswere introduced into time-of-flight mass spectrometer, and ionsgenerated from the central area 2x2 µm2 of the crater were used
to determine depth profiling.
Results and Discussion: Depth profiles of solar wind 4He on
DOS were measured. The penetration range is about 20 nm andthe peak concentration is about 2 x1020 4He cm-3. The fluencecalculated by the profiles is about 8.5 x1014 4He cm-2 consistingwith the accumulated value during solar-wind irradiation-periods
monitored by an on-flight apparatus on the Genesis space craft.
References: [1] Grimberg A et al. 2008, GCA 72: 626-645.
[2] Nagao K et al. 2011, Science 333:1128–1131. [3] Noguchi Tet al. 2011, Science 333:1121–1125. [4] Ishihara M et al. 2010,Surf. Interface Anal. 42: 1598-1602. [5] Ebata S et al. 2012, Surf.
Interface Anal. 44: 635-640.