A gamma and neutron phoswich read out with SiPM for SPRD

Abstract A gamma and neutron phoswich was developed for spectroscopic personal radiation detectors (SPRDs). It consisted of a Φ 25  ×  25 mm NaI(Tl) crystal for gamma detection and a Φ 25  ×  3 mm LiI(Eu) crystal for neutron detection. The phoswich was read out by 8  ×  8 ch SiPM array (24  ×  24 mm 2 ). Radiations in NaI(Tl) and LiI(Eu) were discriminated by pulse shape, while gammas and neutrons in LiI(Eu) were separated by pulse amplitude. For the LiI(Eu), the gamma equivalent energy for thermal neutrons was measured as 3.6 ± 0.1 MeV, providing satisfactory gamma rejection. For NaI(Tl), the response of SiPM array was well linear in the energy range up to 1408 keV, at which a deviation less than 2% was measured. Digital pulse shape discrimination (PSD) was implemented with an 8-bit digitizer running at 50 MSPS sampling rate and offline analysis. The signal pulses from NaI(Tl) and LiI(Eu) showed significant difference in falling edge allowing effective PSD. The best figure of merit (FOM) was measured as 4.4 ± 0.2 with optimized parameters, providing excellent PSD performance. The energy resolutions for 661.6 keV gamma rays in NaI(Tl) and thermal neutrons in LiI(Eu) were measured as 7.0 ± 0.2% and 11.2 ± 0.2% respectively, with selected PSD threshold.

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