Fast Neutron Spectroscopy with a High-pressure Nitrogen-filled Large Volume Spherical Proportional Counter

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
¹⁴
N(n,α)
¹¹
B and
¹⁴
N(n,p)
¹⁴
C reaction products. These reactions have comparable cross sections and Q-values with the
³
He(n,p)
³
H 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.