  In this study, we have developed a new sub-MeV neutron detector that has a
high position resolution, energy resolution, directional sensitivity, and low
background. The detector is based on a super-fine-grained nuclear emulsion,
called the Nano Imaging Tracker (NIT), and it is capable of detecting neutron
induced proton recoils as tracks through topological analysis with
sub-micrometric accuracy. We used a type of NIT with AgBr:I crystals of (98 +-
10) nm size dispersed in the gelatin. First, we calibrated the performance of
NIT device for detecting monochromatic neutrons with sub-MeV energy generated
by nuclear fusion reactions, and the detection efficiency for recoil proton
tracks of more than 2 um range was consistently 100\% (the 1 sigma lower limit
was 83%) in accordance with expectations by manual based analysis. In addition,
recoil energy and angle distribution obtained good agreement with kinematical
expectation. The primary neutron energy was reconstructed by using them, and it
was evaluated as 42% with FWHM at 540 keV. Furthermore, we demonstrated newly
developed an automatic track recognition system dedicated to the track range of
more than a few micrometers. It achieved a recognition efficiency of (74 +-
4)%, and recoil energy and angle distribution obtained good agreement with
manual analysis. Finally, it indicated the very high rejection power for
gamma-rays.
