A Compact Dual Gamma Neutron Detector Based on NaI(Tl+Li) Scintillator Readout with SiPM

Abstract

Sodium iodide crystal co-doped with thallium and lithium is a promising scintillator with wide application prospects for dual gamma neutron detection. In this study, a compact gamma/neutron detector was developed based on 2-inch NaI(Tl+Li) (NaIL) scintillator readout with 8 × 8 silicon photomultiplier (SiPM) array. Dedicated transimpedance amplifier circuit was developed for the SiPM array. The energy resolution and response linearity with the SiPM array were evaluated and compared to those obtained with photomultiplier tube (PMT) readout. The energy resolution for 661.6 keV gamma rays was measured as 7.0% and 6.5% with SiPM array and PMT, respectively. The linear response of the SiPM array is almost the same as that of the PMT in the energy range up to ~4 MeV. Neutron and gamma pulse shape discrimination was evaluated by acquiring the pulse waveforms with a digitizer (12 bit/250 MSPS) and off-line analysis. The best figure of merit (FOM) was measured as 3.75 for the SiPM array with optimized parameters, close to the performance measured with PMT (FOM = 4.07). The experimental results show that the NaIL scintillator readout with SiPM array exhibit energy resolution equivalent to NaI(Tl) gamma detectors and excellent neutron/gamma discrimination, making it especially suitable for compact devices requiring gamma and neutron dual detection capabilities.

Keywords

• NaI(Tl+Li)
• SiPM
• pulse shape discrimination
• neutron detector
• gamma detector