Abstract
A stepwise acid-etching technique similar to the closed system stepwise etching (CSSE) method developed at ETH Zurich was used to examine the solar wind reservoirs of lunar soil grains. Samples were treated with weak acids (H 2O, H 2SO 3) to facilitate the release of the most shallowly implanted gases. Noble gas abundances and isotopic compositions, including Kr and Xe in some cases, and a few nitrogen data were obtained for mineral or grain-size separates of three lunar soils (plagioclase from 60051, pyroxene from 75081, and <25 ym bulk 79035). The 60051 plagioclase grains, considered to be a possibly unique resource for determining the modern-day solar wind composition, show unusually low contents of solar wind He, Ne, and particularly Ar, but do not otherwise possess any characteristics clearly attributable to a modem-day solar wind exposure. Initial water and acid treatments of the grains, however, release an apparently pure SEP component. The 75081 pyroxene and the size separate of bulk 79035 both yield Kr and Xe compositions in initial etch steps that are characteristic of undiffused solar wind, significantly increasing the database for measurements of solar wind Kr and Xe where possible laboratory thermal diffusion and fractionation effects are not a concern. Pyroxene in particular appears to be a suitable alternative to ilmenite for the purpose of making measurements of this kind. Nitrogen release by acid etching is not at present quantitative, and while it appears possible to obtain reasonable isotopic ratios for solar wind N, we are unable to use the technique to determine solar nitrogen to noble gas ratios. Light noble gases in all three soil separates, other than the aforementioned behavior of 60051, appear to behave in accord with expectations based on acid-etching analyses performed by the Züirich group.
Published Version
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