Optical filtering based neutron/γ-ray discrimination in a phoswich detector

Neutron/-ray (∕) discrimination is a crucial issue in neutron measurements and is usually accomplishedemploying detectors transparent to-rays (3He proportional counters), or techniques forrejection (such asPulse Shape Discrimination). The aim of this work is to test a system able to perform a quasi-digital∕discrimination without using techniques based on pulse shape analysis. The system is based on a phoswichconsisting of a LiCAF:Eu crystal sensitive to neutrons and two LuAG:Ce ceramics sensitive to-rays. Opticalfiltering allows obtaining two separate acquisition channels, which selectively collect the light emitted by onlyone of the two scintillators. Photon induced events are then discarded through an anti-coincidence algorithm.The results show that the proposed technique is actually capable of discarding-induced events, but theimplemented setup downgrades the LiCAF:Eu light collection because of the light attenuation of glasses servingas filters. In some situations, it is preferable to employ the LiCAF:Eu crystal alone, discarding the-inducedevents on the basis of the signal amplitude. Therefore, the discrimination technique proposed with this setupis intended for situations in which the energy of the incoming photons or the pile-up effects related to thehigh fluence rate can generate pulses whose amplitude is comparable to a neutron event. In addition, it wasnoted that some optical filters contain impurities (10B in our case) which capture neutrons lowering the systemdetection efficiency.A Monte Carlo model was also implemented to replicate the system response and predict an optimalconfiguration for further development.