Applications of a phoswich-based detector for fast (∼1-10 MeV) solar neutrons for missions to the inner heliosphere

We describe a phoswich-based detector concept for studies of low energy (∼1-10 MeV) solar neutrons in the innermost heliosphere (R <∼ 0.5 AU). The detector has applications both as a very low mass (<∼1 kg), low power (∼1-2 W) stand-alone instrument, and as a component to enhance the capabilities of more sophisticated instruments, for example, the fast neutron imaging telescope instrument described by Moser et al. [Moser, M.R., Flückiger, E.O., Ryan, J.M., et al. A fast neutron imaging telescope for inner heliosphere missions. Adv. Space Res., in press, this issue, doi:10.1016/j.asr.2005.03.037]. In its most basic form, the detector consists of a small volume (∼1 cm3) of fast organic scintillator completely surrounded by a slow inorganic scintillator. The dimensions of the organic scintillator are chosen to minimize multiple n-p scatterings while retaining adequate sensitivity. The inorganic scintillator provides anti-coincidence protection against energetic charged particles. A single PM tube views light from both scintillators. Pulse shape analysis identifies as potential neutrons those events where only the organic scintillator contributes to the signal. The signal size corresponds to the energy of the recoil proton from an n-p elastic scatter, on average half the energy of the incident neutron. An instrument based on this concept would provide measurements of the neutron flux and, through statistical analysis of recoil proton energies, basic information about the neutron spectrum.