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SIMS studies of Allende projectiles fired into
Stardust-type aluminum foils at 6 km/sec
Hoppe P., Stadermann F. J., Stephan T., Floss C.,
Leitner J., Marhas K. K., and Hörz F. (2006)
Meteorit. Planet. Sci. 41, 197-209.
ABSTRACT
We have explored the feasibility of C, N, and O isotopic
measurements by NanoSIMS and of elemental abundance
determinations by time-of-flight secondary ion mass
spectrometry (TOF-SIMS) on residues of Allende projectiles
that impacted Stardust-type aluminum foils in the laboratory
at 6 km/sec. These investigations are part of a consortium
study aimed at providing the foundation for the
characterization of matter associated with microcraters that
were produced during the encounter of the Stardust space
probe with comet 81P/Wild-2. Eleven experimental impact
craters were studied by NanoSIMS and eighteen by TOF-SIMS.
Crater sizes were between 3 and 190 µm. The NanoSIMS
measurements have shown that the crater morphology has only
a minor effect on spatial resolution and on instrumental
mass fractionation. The achievable spatial resolution is
always better than 200 nm, and C and O isotopic ratios can
be measured with a precision of several percent at a scale
of several 100 nm, which is the typical size of presolar
grains. This clearly demonstrates that presolar matter,
provided it survives the impact into the aluminum foil
partly intact, is recognizable even if embedded in material
of solar system origin. TOF-SIMS studies are restricted to
materials from the crater rim. The element ratios of the
major rock-forming elements in the Allende projectiles are
wellcharacterized by the TOF-SIMS measurements, indicating
that fractionation of those elements during impact can be
expected to be negligible. This permits chemical information
on the type of impactor material to be obtained. For any
more detailed assignments to specific chondrite groups,
however, information on the abundances of the light
elements, especially C, is crucial. This information could
not be obtained in the present study due to unavoidable
contamination during impact experiments.
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