Modeling of Cosmogenic Cr Isotopes Produced in Lunar Rocks Compared With Existing Calculations and Measurements.

Autor: Liu, Bailiang1 (AUTHOR), Guo, Jingnan1,2,3 (AUTHOR) jnguo@ustc.edu.cn, Dobynde, Mikhail I.1 (AUTHOR), Liu, Jia4 (AUTHOR), Zhang, Yingnan1,2 (AUTHOR), Qin, Liping1,2 (AUTHOR)
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Zdroj: Journal of Geophysical Research. Planets. Feb2024, Vol. 129 Issue 2, p1-17. 17p.
Abstrakt: The nucleosynthetic Cr isotope anomalies provides useful information to trace the source and origin of extraterrestrial samples, but it is usually influenced by high‐energy cosmic rays, and evaluating such effect of cosmic rays in lunar samples is especially important. Those cosmic radiation particles (primary particles) can react with lunar materials, creating many secondary particles. Both primary and secondary particles can produce cosmogenic nuclides on the Moon. Radiation Environment and Dose at the Moon (REDMoon) is a novel GEANT4 Monte‐Carlo model built to simulate the interactions of space particles with the lunar surface and subsurface content. Using this model, we simulate the production of cosmogenic Cr isotopes (50Cr, 52Cr, 53Cr, 54Cr) at different depths of lunar surface, and compare the contribution of different reactions generating these nuclides. The results suggest that spallation reactions are the most important process producing cosmogenic Cr isotopes. We also analyze the relationship between 53Cr/52Cr and 54Cr/52Cr predicted by our model and compare it with different Apollo samples. As previously studied, we also find an approximate linear relationship between ɛ53Cr and ɛ54Cr, where ɛ53Cr (or ɛ54Cr) is the relative deviation from the standard 53Cr/52Cr ratio (or 54Cr/52Cr ratio), normalized to 1/10,000. Furthermore, we reveal a change of this linear relationship in different depths of lunar surface. Besides, we investigate how the slopes can be influenced by exposure age and the Fe/Cr ratio. With these additional factors carefully considered, the comparison between our modeled results and the measurements is better than previous studies. Plain Language Summary: Cosmic rays arriving at the Moon can change the isotopic compositions on the lunar surface including chromium isotopes which can be used to constrain the evolution history of the Moon. Here, we use the particle transport model to simulate the high‐energy particles and the chromium isotopes generated in the lunar material by different cosmic ray sources. We compare different processes producing cosmogenic Cr isotopes and suggest that the spallation reactions play the main role. After taking the effect of solar energetic particles and the decay of cosmogenic 53Mn into consideration, we reach a better agreement between our model prediction and the Apollo lunar samples about the relationship between ɛ53Cr and ɛ54Cr. Such an improved analysis of the lunar cosmogenic nuclides contributes to a better understanding of the origin of the Moon. Key Points: We simulate the production rate of cosmogenic 50Cr, 52Cr, 53Cr, 54Cr in lunar terrain with Radiation Environment and Dose at the Moon modelWe compare the contributions of different processes producing Cr isotopesWe analyze the relationship between 54Cr/52Cr and 53Cr/52Cr constraining lunar evolution models [ABSTRACT FROM AUTHOR]
Databáze: GreenFILE
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