urn:nasa:pds:context:instrument:clps_to_2ab_pll.nss 1.0 1.19.0.0 Product_Context 2024-05-13 1.0 Initial version. urn:nasa:pds:context:instrument_host:spacecraft.clps_to_2ab_pll instrument_to_instrument_host 10.1016/j.nima.2023.168063 Peplowski, P.N., Elphic, R.C., Fritzler, E.L. and Wilson, J.T., 2023. Calibration of NASA's Neutron Spectrometer System (NSS) for landed measurements of hydrogen content of the lunar subsurface. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, p.168063. CLPS Task Order 2AB Neutron Spectrometer System (NSS) Spectrometer Neutron Spectrometer The Neutron Spectrometer System is an instrument designed to measure the leakage flux of low-energy neutrons out of the lunar soil. A key determinant of leakage flux in the epithermal energy range (>0.5 eV – 500 keV) is abundance of hydrogen-bearing compounds. NSS gauges the fluxes of neutrons in two energy ranges: a) thermal neutrons, less than 0.5 eV, which respond to both abundance and burial depth of hydrogenous materials, and b) epithermal neutrons, which vary in a different way with hydrogen abundance and burial depth from the thermal neutron population. Together, these two measurements constrain not only water-equivalent hydrogen (WEH) abundance but permit a simple model of stratigraphy (burial depth and lower-layer WEH abundance, assuming the overburden is hydrogen-free). Water-equivalent hydrogen is the weight percent of water that a material would contain if all the detected hydrogen was in the form of H2O. For example, a material containing 1500 ppm H would have a water-equivalent hydrogen content of 1.35 wt.%. NSS consists of gas-proportional counter neutron detectors with a design based on the Lunar Prospector Neutron Spectrometer. NSS will measure any temporal variations of at least 0.5 wt.% water-equivalent hydrogen (WEH) at the lander's location. NSS measurements are also used to infer the probable burial depth and WEH wt.% of a buried layer below otherwise desiccated regolith.