Multiplexed SiPM Readout of Plastic Scintillating Fiber Detector for Muon Tomography

Abstract: Muon tomography is a non-destructive imaging technique that uses cosmic-ray muons to probe dense materials. A plastic scintillating fiber (SciFi) detector with a one-dimensional SiPM array offers a compact, high-resolution solution. However, scaling up the detector area and spatial resolution demands reducing the number of readout channels while maintaining detector performance. To address this challenge, this work presents a multiplexing scheme based on a diode-based symmetric charge division circuit combined with a position-encoding algorithm. Circuit simulations confirm the feasibility of the multiplexing design and guide the selection of suitable diodes to preserve SiPM signal integrity. Electronic tests show that the proposed design exhibits low crosstalk among electronic channels, and preserves linearity over a dynamic range spanning a few to several hundred photoelectrons. Cosmic-ray measurements further demonstrate that the multiplexed SciFi detector achieves a detection efficiency above 95\% and a spatial resolution of about 0.65~mm, with only minor degradation compared to direct readout. These results verify that the proposed method offers a scalable and cost-effective readout solution for large-area muon tomography systems.