SONTRAC-a low background, large area solar neutron spectrometer

SONTRAC will measure 20-250 MeV neutrons from solar flares using scintillator fibers viewed by CCD cameras to track neutron-proton scatters. SONTRAC can also be used to track gamma rays above 20 MeV. Veto shields are used to reject all charged particles. Gamma-ray and neutron events have very different track densities, allowing discrimination between the two. Double neutron-proton scatters allow unambiguous determination of the incident neutron energy and direction. Therefore, SONTRAC is capable of rejecting almost all background except neutrons from the solar direction. SONTRAC would have detected the June 15, 1991 flare with 42/spl sigma/ for 20-100 MeV neutrons, having an effective area of 17 cm/sup 2/ in that energy range. The authors present SONTRAC prototype performance results both for neutrons at threshold energy and for cosmic-ray muons.