A borehole muon detector with SiPM-on-tile technology

TL;DR

This paper presents a borehole muon detector based on SiPM-on-tile scintillator tiles to enable 3D hit reconstruction in a compact borehole form factor. The modular 64-channel unit (140 cm by 80 mm) achieves muon-detection efficiency above $95\%$ and zenith resolution in the range $1.5^{\circ}$–$4.0^{\circ}$, avoiding long scintillator bars and wavelength-shifting fibers. Through laboratory tests and Geant4-based simulations, the detector demonstrates ruggedness, cost-effectiveness, and potential azimuthal improvement by stacking rotated modules and using Graph Neural Network reconstruction. This work broadens muon tomography capabilities in borehole environments with a scalable, practical detector design.

Abstract

We developed a compact and rugged muon detector designed for deployment in boreholes. The detector uses a SiPM-on-tile approach in which silicon photomultipliers are directly coupled to scintillator tiles, thereby eliminating the need for wavelength-shifting fibers and long scintillator bars. The modular design is based on a 64-channel unit, 140~cm in length and 80~mm in diameter, composed of $5 \times 5$~cm$^{2}$ scintillator tiles coupled to SiPMs, powered and read out using off-the-shelf electronics. The detector has an average muon detection efficiency above 95\% and acceptance over 5$^\circ$--60$^\circ$ in zenith and 0$^\circ$--360$^\circ$ in azimuth. Simulations indicate that reconstruction combining hit positions and energy deposits achieves a zenith resolution of 1.5--4.0$^\circ$ across most of the zenith range. This work demonstrates a compact, rugged, and cost-effective borehole muon detector based on the SiPM-on-tile approach, offering a new alternative for muon tomography.

Figures (5)

• Figure 1: Top: basic SiPM-on-tile module (left) and 32-channel half-detector unit (right). Bottom: 3D rendering of 64-channel unit (140 cm long, 80 mm in diameter) highlights the scintillators, DAQ module, Raspberry Pi, and end caps.
• Figure 2: Light yield (left) and efficiency (right) measurement of single tile using cosmic-ray measurement with external trigger.
• Figure 3: Landau measured in cosmic-ray setup of a single tile compared with simulations. A smearing factor was included in the simulation to roughly match the width of the peak in the data.
• Figure 4: Zenith-angle performance in intervals of true zenith angle, obtained using the 3D hit method, the energy-based method, and the graph-neural network method.
• Figure 5: Zenith angle bias (left panel) and resolution (right panel) obtained using the 3D hit method, the energy-based method, and the graph-neural network method.