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J.M. Ryan, J. Macri, M.L. McConnell (UNH)
We report on the latest performance measurements of a prototype detector system for SONTRAC, a solar neutron tracking experiment designed to study high-energy solar flare processes. The full SONTRAC instrument will measure the energy and direction of 15 to 200 MeV neutrons by imaging the ionization tracks of the recoil protons in a tightly packed bundle of scintillating plastic fibers. The prototype detector consists of a 12.7 mm square bundle of 250 micron scintillating plastic fibers. A photomultiplier detects scintillation light from one end of the fiber bundle and provides a detection trigger to an image intensifier/CCD camera system at the opposite end. The image of the scintillation light track is recorded. By tracking the recoil protons from individual neutrons, the kinematics of the scattering are determined, providing a high signal to noise measurement. The predicted energy resolution is 10% at 20 MeV, improving with energy. This energy resolution is in turn used to compute the production time of the neutron at the Sun with an uncertainty of 30 s at 20 MeV, also improving with energy. A SONTRAC instrument will also be capable of detecting and measuring high-energy gamma rays > 20 MeV as a `solid-state spark chamber.' We have evaluated the SONTRAC prototype performance using incident beams of 14-65 MeV neutrons and 20--65 MeV protons and also using minimum ionizing cosmic ray muons. Here we shall summarize the results of these measurements which serve to demonstrate the potential of the SONTRAC design for solar physics measurements.
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