EJ-270 is a 6Li loaded PVT-based plastic scintillator developed by Eljen Technologies and Lawrence Livermore National Laboratories. The 6Li makes it sensitive to thermal neutrons and pulse shape discrimination (PSD) can be utilized to separate the neutron events from γ-ray events. The low cost, large available volumes and environmental stability of EJ-270 makes it an attractive alternative to other fast PSD scintillators such as CLYC. A 48 mm diameter x 15 mm thick cylinder of EJ-270 was coupled to a Hamamatsu R6231-100 PMT biased to 1 kV. Measurements were taken with a moderated 241Am–Be source, on the EMMA instrument at the ISIS Pulsed Neutron and Muon source. EJ-270’s sensitivity to γ-rays was evaluated using a 60Co source. The pulses from the detector were digitised using an Acqiris 12-bit digitizer at 400 MSps.
The high thermal neutron rates on the EMMA instrument necessitated the development of alternative PSD algorithms to the conventional charge integration method favouring speed over raw separation efficiency. Figures of merit of 1.3 for thermal neutrons (~350 keVee) have been demonstrated by other authors using the charge integration method and 500 ns long windows. The first alternative method is by measuring the time to 10% of peak amplitude: for EJ-270 10% of peak amplitude is where neutron and gamma pulse shapes diverge. The second method is called tail sum which is achieved by summing a small number of samples in the tail of the decay. A PSD figure of merit for thermal neutron detector of 1.09 was achieved by using the time to 10% method and 1.26 for the tail sum method using 25 samples, higher figures of merit were achievable for more samples but at the cost of rate capability.