Elemental content from 0 to 500 keV neutrons: Lunar Prospector results

Neutron spectroscopy is a new way to study planetary bodies that have sufficiently thin atmospheres. This technique was demonstrated for the first time with Lunar Prospector around the Moon. Here, we report results for moderated neutrons having energies from 0 to 500 keV that were measured using the anti-coincidence shield (ACS) of the gamma-ray spectrometer. We describe the detection method, followed by data reduction with an emphasis on each data processing step; most steps rely on in-flight calibrations. The behavior of the ACS is well known regarding the measurement of moderated neutrons. We present a map of 0–500 keV neutrons over the whole Moon with a spatial resolution of ∼60 km. Statistical errors per pixel are less than 2%. The resulting map includes information about the hydrogen content, concentrations of Fe, Ti, traces of Sm and Gd, and the atomic mass of the regolith. These data complement other neutron products of Lunar Prospector, namely thermal (0–0.4 eV), epithermal (0.4–100 eV) and fast (0.5–8 MeV) neutrons. The previous unexplored region between 100 eV and 500 keV reveals several high counting rate regions that are also visible in epithermal neutron data.