Characterization of a Resistively Multiplexed SiPM Readout for Position-Sensitive Scintillating Fibre Radiation Detectors

Active stoppers based on scintillating fibres provide fast signal formation, fine segmentation and compact geometry. On the other hand, their implementation requires a readout that can handle many silicon photomultiplier channels and a wide range of light intensities. We present a laboratory characterization of a resistively multiplexed SiPM readout for the Fibre IMPlanter concept. The readout combines 16 SiPM input nodes into four analog outputs. Localized pulsed light excitation was used to scan individual SiPM positions, and the four signals were processed by baseline subtraction, charge integration and normalized charge division reconstruction. In an intermediate signal range, the reconstructed position plane shows distinguishable clusters for the individual inputs, indicating that spatial information is retained after a factor-of-four reduction in readout channels. At low amplitudes, the reconstruction is limited by baseline noise and reduced signal-to-noise ratio. At high amplitudes, the energy proxy signal response is affected by SiPM non-linearity and finite microcell occupancy, while position reconstruction accuracy is limited by distortions of the charge sharing. The results identify the signal range in which resistive multiplexing remains a practical compact readout option for SiPM-based scintillating fibre radiation detectors.