User:Seddon/Lunar Neutron Probe Experiment

The Lunar Neutron Probe Experiment was a lunar science experiment, deployed by astronauts on the lunar surface in 1972 as part of Apollo 17. It remains the only neutron detector to have been operated on an airless planetary body.

Background
Samples returned to Earth by Apollo 11 contained isotopes of Gadolinium that could only be produce naturally by neutron capture. This neutron capture in a natural setting was unique up to this point because the environmental conditions on Earth were not conducive for the production of these isotopes. The Earth has a thick atmosphere that protects materials on its surface from interaction with neutrons. Similarly these isotopes could not be produced on meteorites as they are too small to build up sufficient densities of low energy neutrons suited for capture.

Attempts were made on the Apollo 11 samples to assess the neutron flux density and neutron production present in the moons upper regolith, but such insights lacked foundational understandings of the rate of neutron production, how neutron density varies with depth and the energy spectra of the neutron flux. The Lunar Neutron Probe Experiment aimed to close this gap in understanding by measuring these environmental properties in-situ.

Instrument
The LNPE was a 2 meter long staff that was placed into the upper layer of the Moon's surface regolith. Two distinct types of passive particle track detectors were used to assess the rates of neutron capture. The first was a Cellulose triacetate plastic detector. Boron-10 targets would be used to capture incoming neutrons and would subsequently emit an alpha particle that would subsequently the plastic. The second detector was composed of sheets of Muscovite which would identify the fission products that resulted from neutron capture by Uranium-235 foil. Both of these detectors would provide particle path traces. Assessing the neutron energy spectra was provided via cadmium absorbers as well as evaluating the levels of neutron capture by three capsules containing potassium bromide that would produce two isotopic products of krypton.

Operation and deployment
The instrument was stored in the Modularized Equipment Stowage Assembly during flight to moon. Once Apollo 17 reached the surface, the astronauts placed the LNPE on the Lunar Roving Vehicle at the beginning of the missions first EVA. Once the Apollo Lunar Surface Experiments Package had been deployed, a sample core was drilled at a location 40 meters north of the ALSEP's central. The resultant borehole served as the location for the LNPE, once the instruments sections were joined together and activated. The location of the borehole was placed it behind a rock one meter in size. This rock should have helped limit the possibility of contamination as a result of neutron emission from the ALSEP's Radioisotope thermoelectric generator. The experiments was left in place for 49 hours and was retrieved by the Apollo 17 astronauts as they completed the end of the missions third EVA.