Gamma-Ray Source Positioning Using Array NaI(Tl) Detectors in the Radiation Portal Monitors

Radiation portal monitors (RPMs) are globally employed in ports to decrease the illicit trafficking of nuclear materials. Most RPMs are generally considered as threshold devices because they utilize large plastic scintillators, which have limited energy resolution and no position sensitivity, to count the gamma-rays and neutrons emitted by nuclear materials. Hence, we designed an RPM detector system with NaI(Tl) detectors inserted into the plastic scintillators to realize gamma-ray source identification and positioning. In this work, a 2D gamma-ray source positioning algorithm based on the attenuation law and solidangle variation was studied with the simulation results, and the variation of the positioning deviations with the real positions was spline interpolated to calibrate the calculated position. The testing experiment showed a small root mean square error (RMSE) for both x (0.86 cm) and y (1.52 cm) after calibration.