A method combining pulse shape discrimination and pile-up rejection for plastic scintillator detectors based on multiresolution analysis

Abstract This paper introduces a new method for neutron-gamma pulse shape discrimination (PSD) and pile-up signal rejection (PUR) based on multi-resolution analysis (MRA). The method uses a fast wavelet transform to decompose the original signal, extracting approximate components through low-pass filtering and detail components through high-pass filtering. Following reconstruction, the approximate and detail components are analyzed to achieve efficient PSD and PUR, respectively. The experiments used an EJ276 plastic scintillator detector to collect neutron and gamma signals from an Am-Be source for PSD analysis and mixed signals with pile-up pulses (with an additional Na-22 source) for PUR analysis. The MRA method with different wavelet bases was compared to the charge comparison (CC) method in terms of PSD performance across time gate widths and energy ranges. The results show that the CC method works well only with wide time gates and high energy ranges. Except for the Haar wavelet, the MRA method's PSD performance is more stable across different time gates, performing better with smaller time gates. The db3 wavelet provides the best discrimination at small time gates. The PUR results of the MRA method with the db3 wavelet were compared at time gates of 50 ns, 100 ns, 150 ns, and 200 ns. The 200 ns gate offers the best pulse discrimination but loses the most piled-up and neutron signals, increasing the computational load. The 50 ns gate retains the most neutron signals with the lowest load but has the least PSD. Based on users' needs, the ideal time gate for high count rate neutron-gamma PUR and PSD measurements is between 50 ns and 100 ns.