FPGA based field deployable instrumentation system for neutron time of flight sub nanosecond coincidence spectroscopy

In this report, we present a novel FPGA based electronics architecture for sub-nanosecond coincidence spectroscopy in a neutron time-of- flight system employing the Associated Particle Technique (APT).. In the APT [S. MITRA, J.E. WOLFF, et.al,,] the alpha particle associated with a 14 MeV neutron produced by the 3H(d,n)4He reaction in the neutron generator is emitted in nearly the opposite direction. When a neutron collides with the soil matrix, one probable interaction is an inelastic scattering by a C atom producing the characteristic gamma-ray emission. The elapsed time between detection of the alpha particle and detection of the gamma-ray reveals the distance traveled by the neutron and provides the depth of neutron interaction with C in the soil as shown in Fig.l. Since 14 MeV neutrons travel at a speed of 5 cm/ns, it is important to achieve sub nanosecond time resolutions to be able to resolve depth profiles of C layers less than 5 cm thick.