Development of a multi-channel gamma-blind fast neutron detector based on wavelength shifting fibers embedded in a ZnS:Ag epoxy mixture

This paper presents a fast neutron detector based on elastic scattering with hydrogen, a silver-activated zinc sulfide scintillator to convert the recoil proton energy to light, and wavelength-shifting fibers (WLSFs) to collect the scintillation light. The detector uses silicon photomultipliers (SiPMs) to recognize individual scintillation photons and a digital filter algorithm based on single photon counting to find clusters of photons belonging to neutron events. The detector presented in this paper features four detection channels, arranged in a 2 x 2 square. The sensitive volume of each detection channel covers a similar to 5mm by similar to 5mm area from the frontal direction, is 3 cm long, and contains 49 WLSFs. The detector is versatile and performs well under different conditions. Its performance can be tuned to match different applications by simply changing some parameters of the digital filter algorithm. This is illustrated in this paper by extensive measurements in different environments. Using one set of parameters, the detector achieved a gamma-blindness of 10-8 with an intrinsic neutron detection efficiency of similar to 1%. With another set of parameters and with lower requirements for gamma blindness, the intrinsic neutron detection efficiency was increased to similar to 11%. Yet another set of parameters allows the detector to time incoming fast neutrons with an accuracy of similar to 60ns. Additionally, the decay time of the scintillation light created by neutron events was measured, falling to 10% of its peak value in similar to 10 mu s. Finally, the detector was exposed to strong gamma radiation for a prolonged time to test its radiation resistance. The detection efficiency dropped about linearly with the accumulated gamma fluence, reaching a drop of 40% compared to the initial efficiency at a total gamma fluence of similar to 2 & sdot;1013 cm(-2).