New techniques for Fast Neutron Imaging and Spectroscopy

The detection of fast neutrons has important applications in several fields including solar, geospace and planetary physics. The Sun produces neutrons over a wide range of energy during solar flares that provide information on the accelerated particle population. In addition, fast neutrons, produced in the Earth's atmosphere (and other planetary atmospheres) by the interaction of galactic cosmic rays and solar energetic particles, are an important but poorly measured component of the radiation environment in the inner magnetosphere. At Earth, through their decay, they are responsible for populating the inner radiation belt with fast protons. Neutrons are challenging to detect and measurements of them typically suffer from high background rates. High-energy neutrons (>50 MeV) pose even more challenges, because the traditional double-scatter technique based on a time-of-flight (ToF) measurement is limited by short flight paths and small detector sizes characteristic of small satellite platforms. At these high energies, the recoil proton is likely to escape the detector volume, degrading the energy and angular resolution. Long handcuffed by inadequate technology, it is now possible to perform high-energy neutron measurements inside a large monolithic detector by imaging the recoil proton tracks, thus eliminating the need for a time-of-flight measure. The concept is based on a spectrometer assembled from numerous thin hydrogenous scintillating fibers that allow ionization track imaging. The enabling technologies are in the form of (1) new position sensitive, multi-anode, micro-channel plate/photomultipliers (MCP-PMTs) capable of fine grained readout and (2) techniques and procedures for fabricating a space-qualified large detector. Such a Fiber Bundle Neutron Tracker equipped with these sensors can provide high-resolution, fine grained, imaging of fast neutron scatters. We discuss below applications mainly in solar physics but also in radiation-belt physics and planetary physics. Maturing the technology for a possible small satellite mission is important at this time to complement current and upcoming Fermi, Solar Probe Plus, and Solar Orbiter and IMAP missions. This proposed effort builds on optoelectronic technology advancements and experience in fabricating bundles. In addition to the above applications, improved knowledge of atmospheric neutrons themselves, including spatial and temporal variations, are valuable because neutron-induced single event upsets in avionics systems constitute a reliability problem (Leray 2007). Furthermore, neutrons are penetrating, dangerous and abundant, so they pose a health and safety risk to astronauts and aircraft personnel (Dyer 2002). Neutrons also constitute a major background for other NASA assets in LEO (e.g., Wunderer et al. 2006; Ormes et al. 2007). If successful, the proposed work will result in compact, low-mass, low-power neutron detector technology enabling opportunities to detect Heliospheric neutrons on small satellites and/or deep-space probes. We propose a follow-on two-year H-TIDeS Instrument and Technology Development (ITD) program to raise the technical readiness level (TRL) of promising compact, low-power instrumentation for measuring neutrons (between 20-200 MeV) from small satellite (and aircraft) platforms, with the goal of being able to propose such instruments for CubeSat, Explorer, and deep-space (e.g., inner Heliosphere) platforms. We start with experience and equipment acquired from earlier investigations including a currently funded H-Tides grant (FY17-FY19).

Support NASA's Heliophysics strategic science objectives to understand the Sun and its interactions with Earth and the solar system, including space weather. This will be achieved by developing/demonstrating instrumentation technology necessary to address the following science goals: Explore the physical processes in the space environment from the Sun to the Earth and throughout the solar system; Advance our understanding of the connections that link the Sun, the Earth, planetary space environments, and the outer reaches of our solar system; Develop the knowledge and capability to detect and predict extreme conditions in space to protect life and society and to safeguard human and robotic explorers beyond Earth.

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