Study of sampling rate influence on neutron-gamma discrimination with stilbene coupled to a silicon photomultiplier

Choosing a digitizer with an appropriate sampling rate is often a trade-off between performance and economy. The influence of sampling rates on the neutron-gamma Pulse Shape Discrimination (PSD) with a solid stilbene scintillator coupled to a Silicon Photomultiplier was investigated in this work. Sampling rates from 125 MSPS to 2 GSPS from a 10-bit digitizer were used to collect detector pulses produced by the interactions of a Cf-252 source. Due to the decreased signal-to-noise ratio (SNR), the PSD performance degraded with reduced sampling rates. The reason of PSD performance degradation was discussed. Then, an efficient combination of filtering and digital signal processing (DSP) was then applied to suppress the timing noise and electronic background noise. The results demonstrate an improved PSD performance especially at low sampling rates, down to 125 MSPS. Using filtering and DSP, the ascribed Figure of Merit (FOM) at 125 keVee (± 10 keVee) increased from 0.95 to 1.02 at 125 MSPS. At 300 keVee and above, all the FOMs are better than 2.00. Our study suggests that 250 MSPS is a good enough sampling rate for neutron-gamma discrimination in this system in order to be sensitive to neutrons at and above ~ 125 keVee.