High-precision measurement of the Prompt Fission Neutron Spectrum (PFNS) requires a detector system capable of simultaneously covering a wide energy range (from keV to 20 MeV) and achieving a low detection threshold. In traditional single-channel readout modes, high-gain settings required for detecting keV-level neutrons inevitably cause electronic saturation (clipping) of high-energy signals, rendering conventional Pulse Shape Discrimination (PSD) methods based on charge integration or zero-crossing ineffective. To resolve the conflict between low detection threshold and large dynamic range without increasing the complexity of electronic channels, this paper proposes a novel particle identification method based on the analysis of saturated waveforms in liquid scintillators.
The proposed method exploits the distinct differences in the slow decay components (delayed fluorescence) of neutrons and gamma rays, which remain distinguishable even when the fast components are saturated. A two-dimensional feature correlation of “Time over Threshold (ToT)” versus “Tail Charge (Q_tail)” was constructed to recover particle identification capabilities in the saturation region. Specifically, to eliminate the interference of non-linear electronic ringing oscillations during the recovery from saturation, a fixed delay time (t_delay = 30 ns) was introduced to the integration start time of the tail charge.
To validate the algorithm, an experiment was conducted using a ²³⁸Pu−¹³C neutron source with a simultaneous dual-gain data acquisition system. The non-saturated waveforms from the low-gain channel served as the “ground truth” reference to perform an event-by-event correlation analysis with the saturated waveforms from the high-gain channel. Experimental results demonstrate that the new method successfully achieves effective neutron-gamma separation in the deep saturation region while retaining the excellent identification ability for low-energy neutrons with a threshold as low as ~100 keVee. Compared with the mainstream dual-gain readout scheme, this technique significantly extends the effective dynamic range of single-channel measurements and reduces the requirement for electronic channels and data throughput by 50%, providing an efficient and cost-effective technical solution for constructing largescale neutron detector arrays for PFNS measurements.