The Lunar Vulkan Imaging and Spectroscopy Explorer (Lunar-VISE) mission consists of a suite of instruments to explore the Gruithuisen Domes located in the northern lunar hemisphere. One of instruments to be mounted on a rover is a gamma ray and neutron spectrometer. The spectrometer uses a Li-6 enriched Cs26LiYCl6 (CLYC) scintillator to detect both gamma rays and neutrons. The design of the instrument balances mass, power and performance to obtain high-quality gamma ray spectroscopy with a 6.4-cm diameter, CLYC crystal encased in a gadolinium shell to veto thermal neutrons. To obtain a measure of the thermal neutron albedo to assess the concentration of local neutron moderating materials, a 5.0-cm diameter CLYC without a gadolinium shell is used to measure the full spectral, neutron flux. To minimize power, the system design utilizes a multi-channel configuration to provide pulse shape analysis and spectroscopy using a single, readout channel.
There is strong evidence that water-ice is relatively abundant within permanently shadowed lunar surface materials, particularly at the poles. Evidence for water-ice has been observed within the impact plume of the LCROSS mission and is supported by data gathered from the Lunar Exploration Neutron Detector (LEND) and the Lunar Prospector Neutron Spectrometer (LPNS). Albedo neutrons from the Moon are used for detection of hydrogen, where the epi-thermal neutron flux decreases as hydrogen content increases. The origin on the concentration of water within permanently shadowed regions is not completely understood, and the Lunar Polar Hydrogen Mapper (LunaH-Map) mission is designed to provide a high-resolution spatial distribution of the hydrogen content over the southern pole using a highly elliptical, low perilune orbit. The LunaH-Map spacecraft is a 6U cubesat consisting of the Miniature Neutron Spectrometer (Mini-NS). Mini-NS is not collimated, requiring a low altitude to achieve a higher spatial resolution compared to previous missions. To develop a compact neutron detector for epi-thermal neutrons, the Mini-NS comprises of 2-cm thick slabs of CLYC (Cs2LiYCl6), which provide a sensitivity similar to a 10-atm, 5.7-cm diameter He-3 tubes, as used in LPNS. The Mini-NS digital processing electronics can discriminate by shape and height to determine signal (albedo neutrons) from background (cosmic rays). The Mini-NS achieves a total active sensing area of 200 cm2 and is covered with a cadmium sheet to shield against thermal neutrons. The research and development on the detector modules show a robust design ready for space flight.
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