A Study of Position-Sensitive Solid-State Photomultiplier Signal Properties

Abstract

We present an analysis of the signal properties of a position-sensitive solid-state photomultiplier (PS-SSPM) that has an integrated resistive network for position sensing. Attractive features of PS-SSPMs are their large area and ability to resolve small scintillator crystals. However, the large area leads to a high detector capacitance, and in order to achieve high spatial resolution a large network resistor value is required. These inevitably create a low-pass filter that drastically slows what would be a fast micro-cell discharge pulse. Significant changes in the signal shape of the PS-SSPM cathode output as a function of position are observed, which result in a position-dependent time delay when using traditional time pick-off methods such as leading edge discrimination and constant fraction discrimination. The timing resolution and time delay, as a function of position, were characterized for two different PS-SSPM designs, a continuous 10 mm × 10 mm PS-SSPM and a tiled 2 × 2 array of 5 mm × 5 mm PS-SSPMs. After time delay correction, the block timing resolution, measured with a 6 × 6 array of 1.3 × 1.3 × 20 mm3 LSO crystals, was 8.6 ns and 8.5 ns, with the 10 mm PS-SSPM and 5 mm PS-SSPM respectively. The effect of crystal size on timing resolution was also studied, and contrary to expectation, a small improvement was measured when reducing the crystal size from 1.3 mm to 0.5 mm. Digital timing methods were studied and showed great promise for allowing accurate timing by implementation of a leading edge time pick-off. Position-dependent changes in signal shape on the anode side also are present, which complicates peak height data acquisition methods used for positioning. We studied the effect of trigger position on signal amplitude, flood histogram quality, and depth-of-interaction resolution in a dual-ended readout detector configuration. We conclude that detector timing and positioning can be significantly improved by implementation of digital timing methods and by accounting for changes in the shape of the signals from PS-SSPMs.

Characterization of Large-Area SiPM Array for PET Applications

“…One way to improve the effective usable area of a SiPM array is to use large-area SiPM arrays or position sensitive SiPMs (PS-SiPMs) [19-23]. Crystal arrays with pitch sizes of 0.45 mm have been clearly resolved using PS-SiPMs and the effective area of the photodetector can be > 90% [20-21].…”

CHERENCUBE: Concept definition and implementation challenges of a Cherenkov‐based detector block for PET

“…35,36 These approaches, however, are either still prototype concepts or focus on providing only multiple timestamps per pixel, without the position information per fired microcell. On the other hand, currently available positionsensitive photodetectors detecting either the center of gravity of a group of fired cells (i.e., not individual coordinates as required) 37,38 or providing multiple signals per sensor 39 have an intrinsic spatial resolution in the range of several hundreds of micrometers. Thus, the implementation of the introduced detection concept depends on further photodetector developments.…”

Characterization of Linearly Graded Position-Sensitive Silicon Photomultipliers

“…A more traditional approach is implemented in the PS-SSPM, designed and produced by RMD, whose working principle is close to the one of the position-sensitive photomultiplier tubes [3] [4]. In this case, a two-dimensional resistive network connects all the microcells of the detector, and splits the charge generated by each microcell among the four readout channels according to the cell position.…”