Spectrometer for neutron and gamma-ray detection at the distances less than 100 solar radii from the Sun

Solar neutrons with energies <5 MeV can't be detected in the near-Earth space due to the both its decay and decreasing of its fluxes with distance from the Sun. So solar neutron observations near the Sun compared with near-Earth ones allow studying acceleration of ions up to significantly smaller energies, what occurs considerably more often. Besides that near-Sun low energy neutron observations are important for search for non-flare ion acceleration on the Sun. For project InterHelioProbe we have proposed spectrometer of neutrons with energies 0.055 MeV. LiI(Eu) crystal 4*3 cm enriched in 6 Li , surrounded by a plastic scintillator 1-3 cm thick loaded with 10 B is used as a detector. Neutrons will undergo elastic scattering with the hydrogen in the plastic. A delayed coincidence within a window of 0.1 - 10 µs in either scintillator is a signature of a neutron, with the initial fast plastic signal pulse height being a direct measure of the incident neutron's energy. A fast charged particle will be vetoed as simultaneous signals in both scintillators. Gamma's with energies 0.03-10 MeV will be identified too as signals in LiI alone. Calculated effective area for normal neutron incidence is 0.3-5.6 cm2 . Estimated effective area for gamma detection is 3-12 cm2 . Mass of the instrument is <1.5 kg. Power of the detector is about 1.5 watt, needing telemetry - 40 b/s.