Computer Science
Scientific paper
Jan 1999
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999phdt........49b&link_type=abstract
Thesis (PhD). OPEN UNIVERSITY (UNITED KINGDOM), Source DAI-C 61/01, p. 229, Spring 2000, pages.
Computer Science
Scientific paper
A variety of lunar soils (bulk soils, grain size fractions and mineral separates) and regolith breccias were studied for nitrogen abundance and isotopic composition and argon isotopic ratios (although the latter is semi-quantitative) using high resolution stepped combustion and pyrolysis extraction. The vast majority of the nitrogen is of solar wind origin with anticipated 36Ar/38Ar and C/N ratios. Studies of the finest (<10μm) grain size fraction of A12023 and the analysis of an agglutinate separate has shown that agglutinates and complex particles are not the location of a postulated, isotopically light ancient solar wind component. Complex particles liberate their nitrogen δ15N of ~+20‰, upon sample melting above 1050°C. Hence the previously accepted pure spallogenic nitrogen has been shown to be a mixture of the volume-correlated component admixed with minor amounts of spallogenic nitrogen. The low temperature, isotopically heavy nitrogen (NLT) component is believed to be fractionated solar wind, with δ15N ~+110‰. Current studies of immature soils have suggested a recent solar wind isotopic composition of ~+40‰. Hence, isotopic variation in the lunar regolith between ancient and recent solar wind may be as little as 2%, which is consistent with noble gas studies by previous workers. The use of conjoint combustion and pyrolysis extractions has shown that ~3% of the isotopically light nitrogen, NHT, is combustible and possibly not of a solar origin. Several possible sources have been investigated, although the most viable explanation is Fe0, resulting from the reduction of Fe 2+ by reactions with implanted solar wind hydrogen. Interestingly, the isotopic composition of this component (δ15N = -186‰) is similar to that observed in lunar breccias (δ15N ~ -210‰) and may indicate a similar origin for the nitrogen. Overall the data obtained in this study has added some new and interesting observations to the current field of lunar science. This work has detracted from the non solar nitrogen model to account for the isotopic variation in the lunar regolith, but has added some new constraints to the end-member compositions to invoke a solar origin for the observed variation.
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