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PI : Wataru Fujiya

Title : Extended study on the irradiation history of the Itokawa asteroid by light element and noble gas analyses

Abstract

We plan to carry out a combined analysis of lithium- and boron-isotopes, and noble gases including krypton and xenon in order to investigate the irradiation history of the Itokawa asteroid. Because the HAYABUSA samples are derived from the asteroid surface, signatures of implanted solar wind and cosmogenic components are expected to be detected. These light elements and noble gases are ideal tools for investigation of irradiation processes by solar wind and cosmic rays because solar wind and cosmogenic components exhibit highly distinct isotopic compositions with respect to different origins. Also, solar wind compositions of the light elements could shed light on spallation reactions caused by solar energetic particles in the Sun’s photosphere. In our previous work on the HAYABUSA samples allocated for the 1st international A/O for HAYABUSA sample investigation, we detected cosmogenic B (resulting in lower 11B/10B than solar) for one of the HAYABUSA grains. Therefore, we will continue and extend our previous study with more attention to the search for cosmogenic components. For Li- and B-isotope measurement we will utilize the NanoSIMS 50, a high sensitivity and high spatial resolution Secondary Ion Mass Spectrometer (SIMS), while we will perform noble gas analysis with a high sensitivity Noblesse noble gas mass spectrometer with multi-ion counting collection. We will conduct these analyses at Max Planck Institute for Chemistry (Li and B) and at University of Heidelberg (noble gases).

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