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Solar wind noble gases and nitrogen in metal from lunar soil 68501Noble gases and N were analyzed in handpicked metal separates from lunar soil 68501 by a combination of step-wise combustions and pyrolyses. Helium and Ne were found to be unfractionated with respect to one another when normalized to solar abundances, for both the bulk sample and for all but the highest temperature steps. However, they are depleted relative to Ar, Kr and Xe by at least a factor of 5. The heavier gases exhibit mass-dependent fractionation relative to solar system abundance ratios but appear unfractionated, both in the bulk metal and in early temperature steps, when compared to relative abundances derived from lunar ilmenite 71501 by chemical etching, recently put forward as representing the abundance ratios in solar wind. Estimates of the contribution of solar energetic particles (SEP) to the originally implanted solar gases, derived from a basic interpretation of He and Ne isotopes, yield values of about 10%. Analysis of the Ar isotopes requires a minimum of 20% SEP, and Kr isotopes, using our preferred composition for solar wind Kr, yield a result that overlaps both these values. It is possible to reconcile the data from these gases if significant loss of solar wind Ar, Kr and presumably Xe has occurred relative to the SEP component, most likely by erosive processes that are mass independent, although mass-dependent losses (Ar greater than Kr greater than Xe) cannot be excluded. If such losses did occur, the SEP contribution to the solar implanted gases must have been no more than a few percent. Nitrogen is a mixture of indigenous meteoritic N, whose isotopic composition is inferred to be relatively light, and implanted solar N, which has probably undergone diffusive redistribution and fractionation. If the heavy noble gases have not undergone diffusive loss, then N/Ar in the solar wind can be inferred to be at least several times the accepted solar ratio. The solar wind N appears, even after correction for fractionation effects, to have a minimum delta N-15 value equal to or greater than +150% and a more probable value equal to or greater than +200%.
Document ID
19950035333
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Becker, Richard H.
(Univ. of Minnesota, Minneapolis, MN United States)
Pepin, Robert O.
(Univ. of Minnesota, Minneapolis, MN United States)
Date Acquired
August 16, 2013
Publication Date
September 1, 1994
Publication Information
Publication: Meteoritics
Volume: 29
Issue: 5
ISSN: 0026-1114
Subject Category
Lunar And Planetary Exploration
Accession Number
95A66932
Funding Number(s)
CONTRACT_GRANT: NAGW-3336
CONTRACT_GRANT: NAG9-60
Distribution Limits
Public
Copyright
Other

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