We present a fast neutron spectroscopy system based on a nitrogen-filled,
large volume gaseous detector, the Spherical Proportional Counter. The system
has been successfully operated up to gas pressure of 1.5 bar. Neutron energy is
estimated through measurement of the 14N(n,a)11B and 14N(n,p)14C reaction
products. These reactions have comparable cross sections and Q-values with the
3He(n,p)3H reaction making nitrogen a good alternative to 3He use for fast
neutron detection. Two detectors were built at the University of Birmingham and
are currently used for the measurement of fast and thermal neutrons in the
University of Birmingham and the Boulby underground laboratory, respectively.Comment: 3 pages, 6 Figure