The researchers used LRO’s Lunar Exploration Neutron Detector (LEND) instrument to detect signs of ice deposits by measuring moderately energetic “ectothermal” neutrons. Specifically, the researchers used LEND’s Collimating Sensor for Exothermal Neutrons (CSETN), which has a fixed field of view of 30 kilometers (18.6 miles) in diameter. Neutrons are produced by high-energy galactic cosmic rays that come from powerful deep space events, such as exploding stars, and impact the moon’s surface, destroying regolith atoms and scattering subatomic particles called neutrons. Neutrons originate from depths of up to about 3.3 feet (meters) and ping-pong through the regolith, hitting other atoms. Some are guided into space, where they are detected by LEND. Since hydrogen has approximately the same mass as a neutron, neutrons lose relatively more energy in collisions with hydrogen than in collisions with the most common regolith elements. Therefore, if hydrogen is present in the regolith, its concentration will correspondingly reduce the number of medium-energy neutrons observed.
