Multiplexed SiPM Readout of Plastic Scintillating Fiber Detector for Muon Tomography

TL;DR

This work tackles the channel-count challenge in large-area muon tomography by introducing a diode-based symmetric charge-division multiplexing scheme with a position-encoding algorithm for one-dimensional SiPM readout. Circuit simulations guided diode choice and demonstrated feasibility, while a 21-channel SiPM deployment encoded into 7 electronic channels (plus a direct channel) achieved low crosstalk and preserved linearity from $\sim$10 to 122 p.e. Cosmic-ray tests showed the multiplexed SciFi module reaching $>95\%$ detection efficiency and $\approx 0.65\ \mathrm{mm}$ spatial resolution, with only modest degradation compared to direct readout. The method reduces electronics shouldering by about a factor of $3$ (and can be extended to more channels), offering a scalable, cost-effective readout for large-area muon tomography and potentially other scintillator-based detectors. $N_{ m max} = \binom{N_{ m ele}}{2}$ defines the multiplexing limit, guiding future expansions.

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 and high-resolution solution. However, constructing a large-area SciFi detector demands reducing the number of readout channels while maintaining detector performance. To address this challenge, we present a multiplexing scheme based on a diode-based symmetric charge division circuit combined with a position-encoding algorithm, enabling up to $N_{\textrm{SiPM}}^{\textrm{max}}=C^{2}_{N_{\textrm{ele}}}$ SiPM channels to be read out using only ${N_{\textrm{ele}}}$ electronic channels. Circuit simulations confirm the feasibility of the multiplexing design and guide the choice of appropriate diodes to preserve SiPM signal integrity. A multiplexed SciFi detector module comprising 21 SiPM channels read out through 7 electronic channels are constructed. Electronic tests show that this module exhibits low crosstalk between electronic channels, and preserves linearity over a dynamic range from $\sim$10 to 122 photoelectrons. Cosmic-ray measurements further show 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 the direct (per SiPM channel) readout. These results verify that the proposed method provides a scalable and cost-effective readout solution for large-area muon tomography systems.

Figures (16)

• Figure 1: Design of a SciFi module, consisting of two staggered layers of 1 mm diameter fibers read out by a one-dimensional SiPM array with 22 channels of $2\times2$ mm channel size.
• Figure 2: (Left) A 22-channel SiPM array and (right) its readout electronics DT5550W based on Citiroc 1A ASICs.
• Figure 3: The multiplexing board to encode 22 SiPM channels into 7 multiplexed outputs and 1 direct output.
• Figure 4: Schematic of the multiplexed SiPM readout, where the signal of each SiPM channel is symmetrically divided into two parts by the diodes, and 21 SiPM channels are encoded into 7 electronic channels.
• Figure 5: Encoding map of 21 SiPM channels and 7 electronic readout channels.