Modification of the Light Noble Gases From Genesis Aluminum Collectors

Details Modification of the Light Noble Gases From Genesis Aluminum Collectors Modification of the Light Noble Gases From Genesis Aluminum Collectors

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh21a1568m&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SH21A-1568

Other

1027 Composition Of The Planets, 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 1099 General Or Miscellaneous, 7599 General Or Miscellaneous

Scientific paper

The Genesis mission returned samples of solar wind (SW) collected over 2 years at the L1 point for earth- based laboratory measurements. The main goal of the mission is to obtain accurate, high precision isotopic measurements of trace elements in the SW. Since there are several processes and effects that can alter the laboratory measured value from the true SW value, it is worth trying to quantify these effects. We have been doing that by looking at the light noble gases: helium, neon, and argon, but these results will have implications for other elements as well. First, isotopic fractionation can occur if the processes which accelerate the SW away from the sun are mass- dependent. It has been uncertain how large this effect might be. In an effort to quantify this effect, Genesis collected samples of SW from different flow regimes (slow, fast, CME). Our measurements of these different regimes have tightly constrained the possible isotopic fractionation of neon and argon. Second, there are implantation effects. It is known that implantation at constant velocity results in mass fractionation with depth. Heavier isotopes have higher energy, and thus a larger range. The effect of this is that if all of the gas is not recovered during the measurement, the measured isotopic ratios will be altered from their source values. Surface erosion (such as surface damage of Genesis collectors and sputtering of lunar regolithic material) will make the measured ratios heavier than the source, while incomplete degassing of the sample will make the measured ratios lighter. And third, thermally activated diffusion can alter the initial depth profiles and cause losses of shallowly implanted species, both of which cause preferential loss of the light isotopes. We are currently working on a diffusion experiment to determine the diffusion parameters of the Genesis collector materials and to quantify the changes in the measured ratios from diffusive losses. We maintained individual pieces of two different Genesis collectors, polished aluminum and aluminum on sapphire (AloS), at six different temperatures between 160 C and 360 C for 322 days. And now we are performing step-wise heating on the samples. Helium and neon are measured together in one mass spectrometer, and Ar is cryogenically separated from them and measured in a second mass spectrometer. Preliminary results show higher variation in 3He/4He than 20Ne/22Ne and little variation in 36Ar/38Ar, as expected.

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