Neutron/proton discrimination characteristics of spaceborne neutron monitors

We have developed two neutron monitors to measure energy spectra of the space neutrons in the ISS (International Space Station). One of monitors called as ESPHENEC consists of a spherical polyethylene moderator with 26 cm diameter and three slender 3He position sensitive proportional counters (PSPCs) as thermal neutron detectors. The second monitor called as DRAEMON consists of a spherical polyethylene moderator with 30 cm diameter and nineteen pairs of 6Li- and 7Li-glass scintillators as thermal neutron detectors that are arranged along the orthogonal x-,y- and z-axes of the sphere. To evaluate the discrimination capabilities of the two monitors for thermal neutrons from high-energy protons, their responses to the protons and the thermal neutrons were examined. When the 3He PSPC is used, the proton and the thermal neutron events are easily separated. We can obtain the information only on the thermal neutrons by setting a proper discrimination level. For the 6Li-glass scintillator, it is difficult to set a proper discrimination level due to the overlapping of the pulse height spectra of the thermal neutrons and the protons. From the point of view of neutron/proton discrimination the ESPHENEC is superior to the DRAEMON at present for use as a spaceborne neutron monitor. (S.Y.)