A muon scattering tomography system based on high spatial resolution scintillating detector

TL;DR

This work addresses the need for large-area, high-resolution muon scattering tomography detectors by developing a modular plastic scintillator system with encoded readout and WLS fibers, validated through Geant4 simulations and a fully built MST setup. The approach yields a measured spatial resolution of $1.0$ mm and a per-layer efficiency of about $97.5\%$, enabling clear reconstruction of $2\times2\times2\text{ cm}^3$ test blocks and high-contrast imaging of high-Z materials. The combination of triangular scintillator bars, low-noise readout, and a 4-layer architecture demonstrates a scalable, cost-effective path toward practical MST for border security and nuclear-material monitoring, with potential enhancements from ML/EM reconstruction and exploration of alternative scintillator media.

Abstract

Cosmic ray muon scattering tomography (MST) is an imaging technique that utilizes muon scattering in matter to inspect high-Z materials non-destructively, without requiring an artificial radiation source. This method offers significant potential for applications in border security and long-term monitoring of nuclear materials. In this study, we developed a high-precision plastic-scintillator-based position-sensitive detector with a spatial resolution of 0.09 times the strip pitch. A fully functional, full-scale imaging system was then constructed using four layers of such XY position-sensitive detectors, each with an effective area of 53 cm x 53 cm. This paper details the following key contributions: the Geant4-simulated design and optimization of the imaging system, the fabrication, assembly, and testing of the detectors, and an evaluation of the imaging performance of the completed system.

Figures (22)

• Figure 1: Structural diagram of the Muon Scattering Tomography (MST) system. (Left) Four Super Layers, formed by orthogonally stacking two detection planes, provides the incoming and outgoing muon tracks. (Right) Internal grooving of the scintillator bar with embedded wavelength-shifting (WLS) fiber.
• Figure 2: Geant4 geometry setup for imaging simulation.(a) Model of the complete detector structure.(b) Four cubic targets placement.
• Figure 3: Application of the PoCA algorithm to Geant4 simulation data. (a, b) Reconstructed images for detector spatial resolutions of 1 mm and 3 mm. (c, d) X-axis profiles of the lead brick region (5 mm < $x$ < 15 mm) corresponding to the images above, with error function fit applied to the edge.
• Figure 4: Performance of imaging system with different detector spatial resolutions.
• Figure 5: Scintillating detector structure. (Top) Arrangement of multiple scintillator bars. (Bottom) Parameters of the scintillator bar subject to optimization, including fiber radius (R), groove depth (d), and the offset of the fiber groove from the center. The two grooves depicted are a semi-circular groove (left) and an omega-shaped groove (right).