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Active TRL 4 (started at 3, targeting 6)
The objective of the Lunar OutpOst Neutron Spectrometer (LOONS) task is to fully develop, test, and calibrate a fast neutron spectrometer for characterizing the albedo neutron environment on the lunar surface. LOONS uniquely addresses both scientific and operational needs including a broad range of scientific applications from solar to planetary in addition to a critical need for radiation monitoring in deep space. LOONS is an imaging neutron spectrometer based on the double-scatter technique, capable of providing detailed measurements of energy spectra and angular distributions of fast neutrons (>0.5 MeV to ~150 MeV) and γ rays (0.2 to ~20 MeV) on the lunar surface.
LOONS is a compact, state-of-the-art design based on a simple concept, and the product of decades of development with heritage from multiple successful missions. LOONS is composed of two layers of 4x2 arrays of 5-cm scintillating crystal blocks separated 30 cm center-to-center. Eight crystals in each layer are composed of p-terphenyl which allow for pulse shape discrimination (PSD) given the distinct scintillation light pulse shapes between γ-rays and neutrons (and thus provides gamma-ray/neutron discrimination). Each crystal is readout by an array of roughly thirty silicon photomultipliers (SiPM) that operate at low bias voltage (tens of volts), have low mass (order of grams), and are more durable than vacuum-tube PMTs. Each crystal array is surrounded by an anti-coincidence detector (ACD) composed of thin (5-mm thick) plastic scintillating panels read out on each edge by SiPMs.
In 2026, the plan is to optimize LOONS as an operational-only sensor by trading angular resolution for unprecedented energy range (predicted performance is up to 500 MeV). This design, the neutron Dose of Unknown Radiation Environments (nDURE), employs the double-scatter technique utilizing layered scintillators in two planes that are readout by SiPM arrays and leverage the signal processing developed for LOONS. This instrument will be highly compact and applicable to hand-held opportunities, while providing unprecedented dose coverage in the energy range where dosage is most important for deep space exploration. The plan is to pivot to developing nDURE to be flight ready by no later than 2029.
Neutrons produced in spacecraft structural materials and/or the lunar or Mars regolith contribute significantly to astronaut radiation exposure. However, there is limited experimental data for model development and verification for the purpose of crew health and safety. This drives the need for an instrument which can be used to characterize a crewed volume on a deep space mission. The LOONS detector is expected to improve upon the current State Of the Art (SOA) for neutron spectrum measurements by extending the upper bound of the energy range for the measurements from ~15-20 MeV to >100MeV, with no more than a factor of 4 increase in mass/power/ volume over the current SOA of ~5kg, ~25cm x 25cm x 15cm, and ~6W.
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