Experiments on ion implantation were performed in order to better characterize diffusion of noble gases in lunar soil. (4)He(+) at 50 keV with 5x10(16) ions/cm(2) was implanted into lunar simulants 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 display similar (4)He 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 (ae"EuroaeeeS +/-) 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.

Publication name	JOURNAL OF EARTH SCIENCE　Volume: 22 　Issue: 5 　Pages: 566-577　 Published: OCT 2011
Author(s)	Fu, Xiaohui; Zou, Yongliao; Zheng, Yongchun; He, Huaiyu; Ouyang, Ziyuan
Corresponding author	ZOU Yongliao  ylzou@bao.ac.cn  Chinese Acad Sci, Natl Astron Observ, Beijing 100012, Peoples R China
Author(s) from IGCAS	OUYANG Ziyuan

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