The Local-time variations of Lunar Prospector epithermal-neutron data

TL;DR

This study investigates local-time variations in lunar epithermal-neutron data, finding no diurnal hydrogen variation but identifying temperature effects and measuring neutron leakage depth at approximately 20 cm.

Contribution

It provides the first measurement of the effective leakage depth for epithermal neutrons and clarifies the influence of temperature on neutron count rates.

Findings

No evidence of diurnal hydrogen variation.

Anticorrelation between instrumental temperature and neutron counts.

Measured neutron leakage depth of approximately 20 cm.

Abstract

We assess local-time variations of epithermal-neutron count rates measured by the Lunar Prospector Neutron Spectrometer. We investigate the nature of these variations and find no evidence to support the idea that such variations are caused by diurnal variations of hydrogen concentration across the lunar surface. Rather we find an anticorrelation between instrumental temperature and epithermal-neutron count rate. We have also found that the measured counts are dependent on the temperatures of the top decimeters of the lunar subsurface as constrained by the Lunar Reconnaissance Orbiter Diviner Lunar Radiometer Experiment temperature measurements. Finally, we have made the first measurement of the effective leakage depth for epithermal-neutrons of ~20 cm.