The LEND instrument measures the flux of neutrons from the Moon, which are produced by the continuous cosmic ray bombardment of the lunar surface.
The cosmic rays are sufficiently energetic to break apart atoms in the soil releasing high-energy neutrons that are then slowed down and absorbed by nuclei of elements in the soil. Not all the neutrons are captured by the soil, many escape, creating a leakage flux of neutrons which the LEND instrument will observe.
The distribution of neutron velocities, or measurements of how much they were slowed down before escaping, can tell us much about the lunar soil since it depends on the composition of the soil, and mostly, on the content of hydrogen. Even a fraction of hydrogen as small as 100 ppm is known to make a measurable change in neutron distribution from the surface of celestial bodies with thin or no atmospheres and the hydrogen content can be related to the presence of water.
The LEND instrument is sensitive to the velocity distribution of the neutron emanating from the moon and will provide the necessary spatial resolution to determine if increases in hydrogen concentration can be correlated with permanently shadowed craters on the moon where the temperatures are know to be sufficiently cold to trap water.
- The instrument Lunar Exploration Neutron Detector (LEND) will provide the measurements onboard the NASA Lunar Reconnaissance Orbiter (LRO) which include:
- Creation of high resolution Hydrogen distribution maps with sensitivity of about 100 ppm of Hydrogen weight and horizontal spatial resolution of 5 km.
- Characterization of surface distribution and column density of possible near-surface water ice deposits in the Moon's polar cold traps.
- Creation of a global model of neutron component of space radiation at altitude of 30-50 km above Moon's surface with spatial resolution of 20-50 km at the spectral range from thermal energies up to 15 MeV.
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