Calibration of NASA’s Neutron Spectrometer System (NSS) for landed measurements of hydrogen content of the lunar subsurface
P. N. Peplowski, R. C. Elphic, E. Fritzler, Jack T. Wilson
Abstract
NASA Ames Research Center and the Lockheed Martin Advanced Technologies Center have developed a rugged, low-resource neutron spectrometer instrument to characterize the near-surface hydrogen content of the lunar surface . This Neutron Spectrometer System (NSS) monitors local thermal and epithermal neutron rates to provide information about the depth-dependent distribution of hydrogen to depths of a few tens of cm. As of mid-2022, NSS is currently slated to fly on two NASA Commercial Lunar Payload Services (CLPS) missions; the Astrobotic Peregrine-1 lander to a near-side equatorial location, and the VIPER lunar rover to explore the polar terrain around Nobile crater. We report the results of a science calibration campaign that characterized the performance of the NSS sensors . These measurements were used to benchmark the accuracy of Geant4 radiation transport simulations that provide the energy- and angle-dependent neutron sensitivity of the NSS sensors. This information is a necessary input for converting NSS measurements of the thermal and epithermal neutron leakage flux to constraints on local hydrogen content in regions with otherwise known geochemical composition.