SONTRAC: An imaging spectrometer for MeV neutrons

An instrument capable of unambiguously determining the energy and direction of incident neutrons has important applications in solar physics, environmental monitoring, and medical/radiological sciences. The SOlar Neutron TRACking (SONTRAC) instrument is designed to operate in the neutron energy range of 20–250 MeV. It is based on non-relativistic double scatter of neutrons off ambient protons within a block of scintillating fibers. Using this double-scatter mode it is possible to uniquely determine neutron energy and direction on an event-by-event basis. A fully operational science model of such an instrument has been built and its performance (energy resolution, angular resolution) calibrated at MeV energies. The science model consists of a 5×5×5 cm3 cube of orthogonal plastic scintillating fiber layers. Two orthogonal imaging chains allow full 3D reconstruction of scattered proton particle tracks. We report the results of the instrument development and calibration efforts, and discuss ongoing developmental efforts to improve performance.