Lunar potassium distribution:Results from Chang'E-1 gamma ray spectrometer

The global map of potassium is represented in this paper from Chang’E-1 (CE-1) Gamma-ray Spectrometer (CGRS) for its one-year mission.Assuming a linear relationship between net count rate and its abundance,the average potassium abundance of individual landing sites is used as ground-truth for the calibration to derive the global map of absolute concentration.Although CGRS spectra have a lower signal-to-noise ratio,the translated map still keeps relative variations.As calculated from Apollo,Lunar Prospector,and Kaguya,global potassium map from CGRS shows high concentrations on the lunar nearside and secondary concentrations located in the South Pole-Aitken (SPA) basin on the farside.The comparison with Lunar Prospector potassium map shows a good correlation,though abundances on the highlands of the farside are much lower than that of Lunar Prospector.Since the footprint of CGRS measurements is larger than the sampling radius of each landing site,the calibrated map shows a larger variation range of the scale than that of Lunar Prospector,which was derived using theoretical calculation;namely,the calibrated map has higher values in the areas with high concentration while having lower values for the areas with lower concentration.However,the derived potassium map is more consistent with the lunar sample data than that of Lunar Prospector.