Mapping of the lunar surface by average atomic number based on positron annihilation radiation from Chang’e-1

Abstract

A map of the average atomic number of lunar rock and soil can be used to differentiate lithology and soil type on the lunar surface. This paper establishes a linear relationship between the average atomic number of lunar rock or soil and the flux of position annihilation radiation (0.512‐MeV gamma‐ray) from the lunar surface. The relationship is confirmed by Monte Carlo simulation with data from lunar rock or soil samples collected by Luna (Russia) and Apollo (USA) missions. A map of the average atomic number of the lunar rock and soil on the lunar surface has been derived from the Gamma‐Ray Spectrometer data collected by Chang’e‐1, an unmanned Chinese lunar‐orbiting spacecraft. In the map, the higher average atomic numbers (ZA > 12.5), which are related to different types of basalt, are in the maria region; the highest ZA (13.2) readings are associated with Sinus Aestuum. The middle ZA (~12.1) regions, in the shape of irregular oval rings, are in West Oceanus Procellarum and Mare Frigoris, which seems to be consistent with the distribution of potassium, rare earth elements, and phosphorus as a unique feature on the lunar surface. The lower average atomic numbers (ZA < 11.5) are found to be correlated with the anorthosite on the far side of the Moon.