The regolith evolution of airless bodies, like the Moon, is primarily controlled by impact cratering. Since the Apollo Era, measurements of cosmic ray exposure (CRE)-induced Sm and Gd isotopes in lunar drill cores have provided insights into the secondary neutron spectra in the lunar regolith. Since the production and transport of secondary neutrons vary with the regolith’s chemical composition and depth, the neutron fluence profile can be employed to track the evolution of lunar and asteroidal regolith. We developed a stochastic model that incorporates state-of-the-art cosmogenic production rate calculations for Sm and Gd isotopes in an effort to understand regolith evolution in the presence of meteoroid bombardments. By comparing the simulated depth profiles to those observed in the lunar drill cores from the Apollo 15, 16, and 17 missions, we find that the deviations from a static profile are due to continuous surface meteoroid bombardments. These bombardments result in the formation of nuclear-reworked zones near the lunar surface. Based on the surface neutron fluence of lunar rocks and regolith, our modeling shows that the regolith surface is reset by large impact-induced excavation and deposition of blanket ejecta every few hundred million years.

中文翻译：

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随机园艺和中子捕获效应耦合建模对月球风化层表面重铺的限制

像月球这样的无空气天体的风化层演化主要是由撞击坑控制的。自阿波罗时代以来，对月球钻芯中宇宙射线照射 (CRE) 诱导的 Sm 和 Gd 同位素的测量为了解月球风化层中的二次中子光谱提供了见解。由于二次中子的产生和传输随风化层的化学成分和深度而变化，因此中子注量剖面可用于跟踪月球和小行星风化层的演化。我们开发了一个随机模型，其中结合了最先进的 Sm 和 Gd 同位素宇宙生成速率计算，以努力了解流星体轰击存在下的风化层演化。通过将模拟深度剖面与阿波罗 15、16 和 17 号任务中在月球钻芯中观察到的深度剖面进行比较，我们发现与静态剖面的偏差是由于连续的表面流星体轰击造成的。这些轰击导致月球表面附近形成核改造区。基于月球岩石和风化层的表面中子注量，我们的模型表明，每隔几亿年，大的撞击引起的开挖和覆盖层喷射物的沉积就会重置风化层表面。