Wide-energy characterization of a compact NaI(Tl)-SiPM detector up to 20 MeV using a synchrotron gamma-ray source

Abstract This study presents the characterization of a compact NaI(Tl)-SiPM detector system for wide-energy gamma-ray spectroscopy from 0.511 to 20.28 MeV. The system utilizes a dual-channel architecture with high-gain and low-gain channels to address dynamic range limitations. Performance was calibrated using standard radioactive sources and quasi-monoenergetic gamma rays produced via inverse Compton scattering at the Shanghai Laser Electron Gamma Source (SLEGS) beamline of the Shanghai Synchrotron Radiation Facility (SSRF). A simulation-based analysis revealed a fundamental challenge for spectroscopy with this compact instrument at high energies. While the total detection efficiency remains high at approximately 30%, the corresponding full-energy peak (FEP) efficiency was found to drop to a negligible 0.01% at 20.28 MeV. This low FEP efficiency, a direct consequence of incomplete energy deposition in the detector's limited volume, precludes the use of traditional photopeak-based calibration in the high-energy domain. A calibration was performed across the full energy range using methodologies appropriate for each domain. In the low-energy range, where photopeaks are well-defined, a standard calibration achieved an energy resolution of 6.64% at 0.662 MeV and a linear response with a coefficient of determination R 2 of 0.99993. To address the challenge in the high-energy range, a non-photopeak methodology using a simulation-corrected characteristic inflection point was validated. This approach yielded a non-linear calibration described by a second-order polynomial with an R 2 of 0.99973. This work thus provides a comprehensive characterization and a viable methodology for utilizing compact detectors in wide energy-range applications, indicating their potential as sensors for advanced systems employing spectrum unfolding.