Noble Gas Diffusion Mechanism in Lunar Soil Simulant Grains： Results from ^4He^＋ Implantation and Extraction Experiments

• Published in: Journal of earth science (Wuhan, China) China), 2011-10, Vol.22 (5), p.566-577
• Main Author: 付晓辉 邹永廖 郑永春 贺怀宇 欧阳自远
• Format: Article
• Language: English
• Subjects: Biogeosciences; Earth and Environmental Science; Earth Sciences; Geochemistry; Geology; Geotechnical Engineering & Applied Earth Sciences; 加热实验; 土壤颗粒; 惰性气体; 扩散机制; 提取; 月球土壤; 模拟物; 离子注入
• ISSN: 1674-487X; 1867-111X
• DOI: 10.1007/s12583-011-0207-4

Experiments on ion implantation were performed in order to better characterize diffusion of noble gases in lunar soil. ^4He^＋ at 50 keV with 5×10^16 ions/cm^2 was implanted into lunar simuiants and crystal ilmenite. Helium in the samples was released by stepwise heating experiments. Based on the data, we calculated the helium diffusion coefficient and activation energy. Lunar simulants dis- play similar ^4He release patterns in curve shape as lunar soil, but release temperatures are a little lower. This is probably a consequence of long-term diffusion after implantation in lunar soil grains. Variation of activation energy was identified in the Arrhenius plots of lunar simulants and Panzhihua （攀枝花） ilmenite. We conclude that noble gas release in lunar soil cannot be described as simple thermally activated volume diffusion. Variation of diffusion parameters could be attributed to physical transformation during high temperature. Radiation damage probably impedes helium diffusion. However, bubble radius growth during heating does not correlate with activation energy variation. Activation energy of Panzhihua ilmenite is 57.935 kJ/mol. The experimental results confirm that ilmenite is more retentive for noble gas than other lunar materials.