HR: 10:50h
AN: SH32A-03    [Abstracts]
TI: Genesis Solar Wind Magnesium and Iron Fluences
AU: * Jurewicz, A J
EM: jurewicz@gps.caltech.edu
AF: Arizona St. Univ, Dept. of Geology, Tempe, AZ 85287 United States
AU: Burnett, D S
EM: burnett@gps.caltech.edu
AF: Cal Tech, Geological and Planetary Sciences, Pasadena, CA 91125 United States
AU: Guan, Y
EM: Yunbin.Guan@asu.edu
AF: Arizona St. Univ, Dept. of Geology, Tempe, AZ 85287 United States
AU: Woolum, D S
EM: dwoolum@fullerton.edu
AF: California State U., Dept. of Physics, Fullerton, CA 92634 United States
AB: Fe and Mg fluences are being measured in selected Genesis collector fragments. This study is in pursuit of one of the first goals for the analysis of Genesis samples: measuring the magnitudes of first ionization potential, FIP (or first ionization time) fractionation of solar wind elemental abundances relative to the solar photosphere. Fe and Mg have FIP 7.90 and 7.64 eV respectively. The relative abundances of elements with FIP below 9 eV are of particular interest as they appear unfractionated in spacecraft data, whose measurements are imprecise relative to that eventually expected from analyses of Genesis collectors. In contrast, elements above 9 eV FIP are clearly fractionated. These low FIP elements constitute significant fractions of the terrestrial planets. We are at a very preliminary state in the analyses and have been challenged by surface contamination related to (1) the hard-landing of the sample return capsule upon re-entry, and (2) a photopolymerized silicone film produced in flight. We have determined that the silicone film did not cause significant solar wind attenuation during collection; nevertheless, cleaning of particulates is required for most analyses. For the analysis of Mg and Fe in selected samples, we have found that secondary ion mass spectrometry (SIMS) has sufficient depth resolution to allow us to deconvolve the surface contamination from the underlying solar wind. Simple wet cleaning of particles produced 100-200 micron size areas for SIMS analysis free of visible particles. The shapes of the measured SIMS depth profiles are in reasonable agreement with theoretical profiles based on the solar wind He velocity distributions measured by the LANL solar wind monitors on the Genesis spacecraft. Analyses to date are of the bulk solar wind collected over 27 months during 2002 through April 2004. Silicon metal collectors - the most prevalent collector on Genesis - was selected for Mg analyses. However Fe was expected to diffuse rapidly in silicon at the 150 deg C temperatures expected in the silicon wafers during solar-wind collection, so Si wafers coated with a diamond-like-carbon (prepared at Sandia Labs by T. Friedman) were selected for Fe analyses. Laboratory implant standards are used to quantify solar wind fluences. The derived fluences in units of per sq. cm were 2.1e12 for Mg and 1.6e12 for Fe. Adopting conservative 20 per cent fluence errors gives a solar wind Fe/Mg = 0.76 with an error of 0.22. This agrees well with the AGS photospheric ratio of 0.83, with a 1 sigma error of 0.22 Eventually, be able to lower the Genesis errors in Fe/Mg to a few percent or better. We note that the FIPs for Fe and Mg differ by only 0.3 eV. A better test of FIP fractionation would be to measure a larger range of FIPs. Accordingly, measuring Na (FIP = 5.14) and Si (FIP = 8.151) fluences have a high priority at present.
DE: 6040 Origin and evolution
SC: SPA-Solar and Heliospheric Physics [SH]
MN: Fall Meeting 2005