Hard X-ray continuum from lunar surface: Results from High Energy X-ray spectrometer (HEX) onboard Chandrayaan-1

Abstract The High Energy X-ray spectrometer (HEX) on Chandrayaan-1 was designed to study the photon emission in the range of 30–270 keV from naturally occurring radioactive decay of 238 U and 232 Th series nuclides from the lunar surface. The primary objective of HEX was to study the transport of volatiles on the lunar surface using radon as a tracer and mapping the 46.5 keV line from 210 Pb, a decay product of 222 Rn. HEX was tested for two days during the commissioning phase of Chandrayaan-1 and performance of all sub systems was found to be as expected. HEX started collecting science data during the first non-prime imaging season (February–April, 2009) of Chandrayaan-1. Certain anomalies persisted in this data set and the early curtailment of Chandrayaan-1 mission in August, 2009, did not allow any further operation of HEX. Despite these issues, HEX provided the first data set for 30–270 keV continuum emission, averaged over a significant portion of the lunar surface, including the polar region.