Feasibility of a CsI(Tl)-GAPD Line Radiation Detector for Seafood Contamination Detection

This paper presents the design and performance evaluation of a field-deployable, real-time, multi-channel line radiation detector for imaging radioactive contamination in seafood. The detector integrates scintillator arrays made of thallium-doped cesium iodide (CsI(Tl)) with Geiger-mode avalanche photodiodes (GAPDs) to enable spatially resolved gamma-ray detection. This detector consists of 128 channels arranged in a 4 × 32 configuration, providing a total active area of 98.24 mm × 12.28 mm. The CsI(Tl) scintillator is configured as a 4 × 4 array, with each pixel measuring 3 × 3 × 10 mm³ and wrapped in a TiO₂ reflector. The G APD array possesses the same 4 × 4 geometry, and each pixel has a sensitive area of 3.07 × 3.07 mm². The photon detection efficiency at 540 nm is approximately 30%, with a gain on the order of 10⁶. Signals from 32 individual GAPD channels are multiplexed into four analog outputs via resistive charge division (RCD), enabling the gamma-ray interaction position to be extracted. Subsequently, the multiplexed signals are amplified by a two-stage inverting amplifier with an overall gain of approximately 20 and digitized by a data acquisition system for storage and analysis. Performance is evaluated using a fish sample containing an embedded Na-22 point source, and the source position is reconstructed as heatmaps obtained from line scans at 17 positions with 12 mm spacing. The detector achieves an average energy resolution of 15.9 ± 2.0% at 511 keV, demonstrating uniform performance across all 128 channels. The heatmaps reveal high counts at scan positions corresponding to the Na-22 source within the fish sample, clearly resolving the spatial distribution of gamma rays. These results indicate that the proposed detector can detect and image radioactive contamination during seafood inspection, and future work will investigate the feasibility of a magnetic resonance-compatible radiation detector based on gamma-ray position discrimination.