Brightness temperature is a main index to reflect the energy of microwave radiation of an object. Using lunar brightness temperature data, physical properties of lunar regolith, such as thickness, heat flow and dielectric permittivity, could be interpreted. There are two methods to study brightness temperature distribution of the moon: the first is used to measure lunar brightness temperature by radio observation or spaceborne microwave radiometers, and the second is used to simulate calculation by the physical model. On the basis of the measurements of lunar brightness temperature in the history, this study analyzed the main physical model of lunar brightness temperature, also including its theory and influence factors. The authors concluded that surface and subsurface temperatures of the moon, dielectric properties and layered structure of lunar regolith were the main factors affecting the global brightness temperature of the moon. These factors should be quantified in detail in the future research.
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.
