Study of the thermal neutron detector ZnS(Ag)/LiF response using digital pulse processing

The neutron and gamma responses of a commercial 6Li loaded ZnS(Ag) detector (EJ-420) have been studied using a moderated 252Cf source and a set of pure gamma ray sources (137Cs and 241Am). Digital pulse processing was used to implement the pulse shape discrimination technique in order to well-separate neutrons from gamma-induced events. It was found that in case of a mixed neutron/gamma radiation field (252Cf) pulse-height discrimination technique works quite good for the measurement of the neutron field, but if one desires to reach a gamma-to-neutron sensitivity ratio lower than 0.7 % pulse shape discrimination technique must be implemented. Also, the decay times of the scintillation components of ZnS(Ag)/6LiF were determined by following the so called “peeling method”. The results were compared with some reported values. In order to better understand the shape of the neutron-induced pulses produced by the EJ-420 detector, a measurement with an EJ-440 detector of an alpha source (210Po) was performed. The response of both detectors must be very similar because these are based in ZnS(Ag) scintillator. It seems that for neutron detection with the EJ-420, the scintillation produced by the tritium is most important than the one produced by the alpha particle. Finally, the neutron efficiency and some experimental features of the EJ-420 detector were determined and reproduced respectively by Monte Carlo simulations (GEANT4 9.6).