Evaluation of two thermal neutron detection units consisting of ZnS/6LiF scintillating layers with embedded WLS fibers read out with a SiPM

Two single channel detection units for thermal neutron detection are investigated in a neutron beam. They consist of two ZnS/6LiF scintillating layers sandwiching an array of WLS fibers. The pattern of these units can be repeated laterally and vertically in order to build up a one-dimensional position sensitive multi-channel detector with the needed sensitive surface and with the required neutron absorption probability. The originality of this work arises from the fact that the WLS fibers are read out with SiPMs instead of the traditionally used PMTs or MaPMTs. The signal processing system is based on a photon counting approach. For SiPMs with a dark count rate as high as 0.7 MHz, a trigger efficiency of 80% is achieved together with a system background rate lower than 10−3Hz and a dead time of 30μs. No change of performance is observed for neutron count rates of up to 3.6 kHz.