Neutron Spectrometer

	Neutrons Originate from the Moon. Counts registered by the tin-wrapped (HeSn) and cadmium-wrapped (HeCd) LPNS sensors during successive 32-second integration periods from instrument turn-on (08 Jan. 1998) to 16 Jan. 1998. Lunar orbit insertion occurred on 11 Jan. Counter thresholds were commanded to their operational values late on 14 Jan., as seen by the sharp decrease in counting rates in both counters. Feldman et al., Science, 281, 1489, 1998.
	Thermal Neutron Counting Rate Map. Global map of the thermal-neutron counting rate. Data acquired during mapping cycles 1-12 (16 Jan. 98 thru 27 Jun. 98) are combined and have been partially corrected for instrument response function and variations in the flux of galactic cosmic rays. A basemap constructed using Clementine albedo data showing various lunar features, overlays the thermal-neutron counting rates. Feldman et al., Science, 281, 1489, 1998.
	Fast Neutron Counting Rate Map. Global map of the fast-neutron counting rate. Data acquired during mapping cycles 1-12 (16 Jan. 98 thru 27 Jun. 98) are combined and have been partially corrected for instrument response function and variations in the flux of galactic cosmic rays. A basemap constructed using Clementine albedo data showing various lunar features, overlays the fast-neutron counting rates. Feldman et al., Science, 281, 1489, 1998.
	Simulations and Measurements of Fast/Thermal Neutrons. Correlation of the simulated and measured fast/thermal neutron counting rates (both arbitrary units) as a function of the calculated macroscopic neutron absorption cross section. Bulk compositions of the soils and regolith breccias from the 6 Apollo landing sites and the 3 Luna returned sample sites have been used to calculate the effective absorption cross sections for each site. Feldman et al., Science, 281, 1489, 1998.
	Neutron Measurements and Sample Returns. Correlation between measured thermal-neutron (top) and fast-neutron (bottom) counting rates, and the height of the lunar surface above the mean datum measured by Clementine. Clementine determined altitudes were smoothed to 14.5° spatial resolution to match the footprint size red high fast fluxes, and are identified with a range of compositionally diverse mare basalts. The correlation of measured thermal neutron fluxes with macroscopic absorption cross sections calculated for the Apollo and Luna samples, is fair to good, which is interpreted to indicate that compositions inferred from returned samples are not representative of averages over roughly 450 km diameter areas surrounding each of the landing sites. Feldman et al., Science, 281, 1489, 1998.
	Clementine Predicted Neutron Absorption. Macroscopic absorption cross section as determined from Clementine spectral reflectance Fe and Ti abundances. The original 0.25°x0.25° map has been smoothed using the thermal neutron response function, but is binned in 2°x2° (60x60 km) pixels. Local highs can be seen over the nearside maria and over the SPA basin, where Fe and Ti concentrations are higher than the surrounding highlands. Elphic et al., Science, 281, 1493, 1998.
	Observed Thermal Neutron Absorption. Ratio of the Lunar Prospector fast-to-thermal neutron count rates. This quantity should be directly related to the abundance of thermal neutron absorbers in the regolith. Highs are found over the maria and the SPA basin. Data from the first six months of Lunar Prospector mapping are shown. Elphic et al., Science, 281, 1493, 1998.
	Observed vs Predicted Thermal/Fast Neutron Absorptions. Fast-to-thermal neutron count rate ratio plotted versus Clementine predicted absorption data (black points). Red points come from a more restricted region (20E-180E longitude, 30S-30N latitude). The solid line is an ideal linear relationship that would be expected if Fe, Ti and Ca are the most important absorbing species. Flux ratio values to the left of this line indicate that the calculated values based on Clementine predicted absorptions are too low, and other neutron absorbers are present. Elphic et al., Science, 281, 1493, 1998.
	Tentative Map of Rare Earth Elements. Map of thermal neutron absorbers in addition to Fe, Ti and other major elements implied by Clementine predicted absorptions-derived abundances. We infer these absorbers to be the rare earth elements: Gadolinium and Samarium. The units are in 10^-4 cm²/g. The greatest values are found surrounding the Imbrium basin, approximately colocated with regions rich in KREEP. Elphic et al., Science, 281, 1493, 1998.