Performance evaluation of compact plastic scintillating fiber modules for muon tomography applications

TL;DR

This work tackles the challenge of achieving high-resolution, large-area detectors for muon tomography by designing four compact 100 cm long SciFi modules composed of two staggered layers of 1 mm diameter plastic scintillating fibers read out at one end by a 1D SiPM array with 2 mm pitch. After calibration, clustering, tracking, and alignment, the modules achieve an efficiency above $97\%$ and an intrinsic spatial resolution of $\sigma_d \approx 0.56$ mm, uniformly along their length. A proof-of-principle muon-scattering imaging test with a lead block demonstrates the system’s capability to resolve material profiles via PoCA analysis, highlighting the potential for compact, large-area muon tomography. The results support a scalable path toward cost-effective, high-resolution muon tomography with multiplexed SiPM readout in future large-area deployments.

Abstract

Muon tomography is a non-destructive imaging technique that exploits cosmic-ray muons from multiple directions. Its performance critically depends on the stability, active-area coverage, and spatial resolution of position-sensitive detectors. In this work, we report on the development of four compact scintillating fiber modules, each 100 cm long and composed of two staggered layers of 1 mm diameter fibers. The fibers are read out at one end by one-dimensional silicon photomultiplier arrays with a 2 mm pitch, coupled to Citiroc 1A-based front-end electronics. The modules were characterized with cosmic-ray muons, yielding a detection efficiency above 97% and a mean spatial resolution of about 0.56 mm, with uniform response over different distances from the readout end. An imaging test of a lead block was also performed, and the reconstructed results are consistent with the blocks profile. These results demonstrate the suitability of this detector design for compact and large-area systems in muon tomography applications.

Figures (17)

• Figure 1: The design of one SciFi module with two staggered layers of 1 mm diameter fibers and one-dimensional SiPM array of 2 mm pitch size for sub-millimeter spatial resolution.
• Figure 2: (a) Aluminium alloy mold with machined grooves, (b) first fiber layer placed along grooves of the mold, (c) the complete fiber modules with one end directly coupled to SiPM arrays and the other end covered by ESR film to reflect photons to the readout end, (d) the cross section of a SciFi module with two staggered layers of 1 mm diameter fibers, and (e) one-dimensional SiPM array composed of 22 Hamamatsu S13360-2050VE devices used at the readout end.
• Figure 3: Experimental setup of the SciFi modules with Citiroc1A-based readout electronics. The four short modules provide the muon trigger for the long SciFi modules during the cosmic-ray muon test. Their positions can be adjusted to record muon events at different locations along the long modules.
• Figure 5: (Left) The raw ADC spectrum of one HG amplifier channel used to extract gain and pedestal values. (Right) LG signal after pedestal subtraction as a function of the calibrated HG $N_{\mathrm{pe}}$ for a representative SiPM channel, from which the gain in LG mode is obtained by a linear fit.
• Figure 6: (Left) Calibrated SiPM signals from layer 1 acquired in muon-test mode after pedestal subtraction and gain calibration. (Right) Distribution of the SiPM channel with the maximum $N_{\mathrm{pe}}$ in each event for all four long modules when the short modules were centered at 52.5 cm from the readout end of the long modules.