High count rate pulse shape discrimination algorithms for neutron scattering facilities

The performance of EJ-270, a  6Li loaded pulse shape discriminating plastic scintillator was tested for use in applications with high thermal and epithermal neutron fluxes such as neutron scattering facilities. The short decay time of EJ-270 make it of interest for high count rate applications. To realize this, 4 PSD algorithms were tested. The algorithms were selected based on the potential for high rate applications and simplicity. These algorithms were the charge integration method with and without the addition of a digital low pass filter, a measurement of the time to 10% of peak amplitude and a method we call the “tail sum” which utilizes a digital low pass filter and sums a small number of samples in the tail of each pulse. These algorithms were benchmarked using the figure of merit, the γ-sensitivity and potential rate capability. The charge integration method gave the highest figure of merit of 1.37 using a long window of 272.5 ns but had a γ-sensitivity of 2×10−6 which was poorer than the tail sum algorithm. The tail sum algorithm was able to achieve a figure of merit of 1.36 with a window of 250 ns and a γ-sensitivity on the order of 10−7. Reducing the integration windows to match the fastest algorithm of time to 10% resulted in the tail sum outperforming the other algorithms with a figure of merit of 1.26 and a γ-sensitivity of 6×10−7. The short charge integration method and tail-sum were compared on the EMMA beamline at the ISIS pulsed neutron and muon source. The tails sum demonstrated better separation between the γ-rays and thermal neutron at an incident peak neutron rate of 9.6×105 neutrons per second.