Characterization of stilbene and EJ-276 scintillators coupled with a large area SiPM array for a fast neutron dose rate detector

A 1-inch stilbene and EJ-276 (plastic) organic scintillators were characterized in view of their use in a portable survey meter for fast neutron detection and dose rate measurements in radiation protection. They were coupled with a large area Silicon Photomultiplier (SiPM) array and characterized in terms of neutron/$\gamma$–ray (n/$\gamma$) discrimination capability, count rate linearity, count rate saturation effects, temperature stability and neutron detection efficiency. A Pile-Up Rejection (PUR) algorithm was developed and tested to increase their count rate linearity with increasing dose rate. Results show that the stilbene exhibits better performance compared to the plastic in terms of: Pulse Shape Discrimination (PSD) with a Figure Of Merit (FOM) of 1.5 vs. 1.1, energy resolution (15% vs 20% at 662 keV) and fast neutron efficiency (12% vs. 9% with an AmBe source). For both scintillators, the dose rate response is linear up to 1 mSv/h with a $^{137}$Cs $\gamma$-ray source. With a neutron source, the response is linear, and the FOM is almost constant for dose rates up to 1.5 mSv/h. The PUR reduces the false neutron events by one order of magnitude when the detectors are irradiated with a $\gamma$-ray source up to 10 mSv/h, and it correctly works when irradiated with an AmBe source at 1.5 mSv/h together with a $^{137}$Cs source up to 60 μSv/h. The proposed PUR algorithm is promising but needs to be tested with a higher intensity mixed n/$\gamma$ field. The temperature stability of both detectors was also studied in the temperature range from −10 °C to ＋40 °C. The light yield increases by around 25% for both detectors when reducing the temperature. The variation of the neutron count rate is around 10% in the same temperature range. This work provides a complete overview of the performance of these detectors and a coherent comparison between the two types of scintillators with the same experimental setup.