TERRAPUB Geochemical Journal

Geochemical Journal, Vol. 49 (No. 5), pp. 559-566, 2015

Depth profiling analysis of solar wind helium collected in diamond-like carbon film from Genesis

Ken-ichi Bajo,1 Chad T. Olinger,2 Amy J. G. Jurewicz,3 Donald S. Burnett,4 Isao Sakaguchi,5 Taku Suzuki,5 Satoru Itose,6 Morio Ishihara,7 Kiichiro Uchino,8 Rainer Wieler9 and Hisayoshi Yurimoto1*

1Department of Natural History Sciences, Hokkaido University, IIL, Sapporo 001-0021, Japan
2Applied Modern Physics Group, Los Alamos National Laboratory, Los Alamos, NM 87545, U.S.A.
3CMS/SESE, Arizona State University, Tempe, AZ 85287-1404, U.S.A.
4Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, U.S.A.
5National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
6JEOL Ltd., Musashino, Akishima, Tokyo 196-8558, Japan
7Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
8Graduate School of Engineering Sciences, Kyushu University, Kasuga, Fukuoka 816-8580, Japan
9Institute for Isotope Geology and Mineral Resources, ETH Zurich, Clausiusstrasse 25, 8092 Zurich, Switzerland

(Received January 23, 2015; Accepted June 30, 2015)

Abstract: The distribution of solar-wind ions in Genesis mission collectors, as determined by depth profiling analysis, constrains the physics of ion-solid interactions involving the solar wind. Thus, they provide an experimental basis for revealing ancient solar activities represented by solar-wind implants in natural samples. We measured the first depth profile of 4He in a Genesis collector; the shallow implantation (peaking at <20 nm) required us to use sputtered neutral mass spectrometry with post-photoionization by a strong field. The solar wind He fluence calculated using depth profiling is ~8.5 × 1014 cm-2. The shape of the solar wind 4He depth profile is consistent with TRIM simulations using the observed 4He velocity distribution during the Genesis mission. It is therefore likely that all solar-wind elements heavier than H are completely intact in this Genesis collector and, consequently, the solar particle energy distributions for each element can be calculated from their depth profiles. Ancient solar activities and space weathering of solar system objects could be quantitatively reproduced by solar particle implantation profiles.
Key words: solar wind, depth profile, helium, NASA Genesis mission, post-ionization

*Corresponding author E-mail: yuri@ep.sci.hokudai.ac.jp

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