太阳风对月壤矿物结构和成分特征改造的模拟实验研究

It is diffuclt that distinguishing the origion of lunar grain rims from solar wind implantation and micrometeroit bombardment by the compositional content difference of O, Si, Mg, etc. and the presence of nano particle iron and bubble structure. There was little study in solar wind impact history, currently. For these reasones, we plan to study the structural and compositional change of mineral impacted by solar wind. In the study, technique of ion implantation will be used to simulate the solar wind radiation and the change of mineral structure and chemical composition will be discussed in detail. Plagioclase, pyroxene, olivine, and ilmenite will be implanted by H and He ion, respectively. A high resolution Transmission Electron Microscope is used to image the samples with high resolution and electron diffraction atfer ion implantation. With these images, remaining crystal planes are investigated based on the striation of crystal plane in high resolution image and the distance of diffraction spots in electron diffraction image. Further, the damage sequence and the implantation dose of special crystal plane are determined, and the difference among minerals and crystal planes is analyzed. And then, the relationship among the remaining crystal plane, implantation temperature, implantation dose, crystal structure is discussed. With the analysis of O, Si, Mg content and H, He distribution in the mineral, a relationship between the characters of mineral structure and chemical composition and solar wind implantation would be proposed lastly. According to these results, the characters of mineral structure and chemical composition changed solar wind implantation in amorphous rim, multiple rims, and vesicular rim are discussed. These results will serve to the study of lunar samples achieved in China's Lunar Exploration Program III.

针对当前利用O、Si、Mg等主量元素的含量差异和纳米金属铁及气泡结构的存在与否很难区分月壤颗粒环带的太阳风成因和微陨石撞击成因的问题，以及月表太阳风作用历史研究不足的现状。项目拟立足太阳风作用对矿物微观结构破坏和成分改造特征，利用离子注入技术模拟月表太阳风的作用过程，对斜长石、辉石、橄榄石、钛铁矿等月壤主要组成矿物开展离子注入实验模拟，分析离子注入后矿物的结构破坏和成分变化特征。利用透射电镜的高分辨像和电子衍射斑对矿物颗粒表层结构中的残留晶面进行统计分析，确定晶面破坏的先后次序和对应离子注入剂量，探讨注入离子类型、温度、剂量与斜长石、辉石、橄榄石、钛铁矿等矿物的结构破坏特征之间的关系。结合矿物颗粒中O、Si、Mg等主量元素及H、He等注入元素的含量分析，确定矿物结构和成分变化特征与太阳风作用之间的关系，并探讨月壤颗粒环带的太阳风成因特征和太阳风暴露时间，为探月三期月球样品研究提供参考。

针对当前利用O、Si、Mg 等主量元素的含量差异和纳米金属铁及气泡结构的存在与否很难区分月壤颗粒环带的太阳风成因和微陨石撞击成因的问题，以及月表太阳风作用历史研究不足的现状。本项目以斜长石、辉石、橄榄石和钛铁矿等月球表面主要矿物为研究对象，通过理论分析和实验模拟，分析太阳风作用对矿物晶格的破坏特征和影响因素，主要取得了以下几个方面的研究成果，为认识月壤的演化历史提供了参考：①理论计算了太阳风H和He离子在钙长石、顽辉石、镁橄榄石和钛铁矿中的投影射程，无论是H+还是He+均表现出投影射程在钙长石>顽辉石>镁橄榄石>钛铁矿，此外在相同的辐射剂量下，He+能够运动到矿物更深的位置，因此能够造成更大范围的晶格破坏；②理论计算了太阳风H和He离子对钙长石、顽辉石、镁橄榄石和钛铁矿四种矿物中原子的溅射产额，H+对矿物中氧元素的溅射产额表现为镁橄榄石>顽辉石>钛铁矿>钙长石，并且在太阳风溅射月表矿物的过程中起主导作用的是H+而不是He+；③H+和He+对斜长石的注入模拟实验中发现了一种特殊的结构——裂隙结构，这是注入到斜长石中的高压H2导致晶面爆裂而形成的；④在H+和He+对四种矿物的注入模拟实验中，所有矿物都发生了非晶化，但是非晶化的程度不一样，部分非晶化主要发生在斜方辉石、橄榄石与钛铁矿样品中，完全非晶化则主要发生在斜长石、斜方辉石与橄榄石样品中；⑤在H+和He+对四种矿物的注入模拟实验中，注入后的斜长石样品中发现有气泡的生成；⑥对月表四种主要矿物斜长石、斜方辉石、橄榄石以及钛铁矿在多种辐射条件下的辐射损伤特征进行分析可知，上述四种矿物的非晶化程度均随着辐射剂量的增加而增大；⑦根据上述四种矿物的辐射损伤特征差异可以作为判断月壤样品的大致太阳风暴露年龄的重要指标，从而建立了不同矿物晶格破坏程度对应的太阳风暴露时间标尺。