Single Silicon Photomultiplier Research Articles

A cost-effective field-programmable-gate-array-based pulse processor for biomedical imaging applications

ObjectiveThis paper presents the design and evaluation of a cost-effective, high-spatial resolution, multichannel, field-programmable gate array (FPGA)-based readout system for Positron Emission Tomography (PET) detectors suitable for clinical and pre-clinical work in cancer and other diseases. A key challenge in PET imaging is the precise measurement of the time of arrival and energy of gamma photons originating from positron annihilation, along with the position of interaction within the detector. These parameters enhance image quality by improving coincidence detection, excluding Compton-scattered photons, and improving system spatial resolution. We developed a 16-channel readout system using single silicon photomultiplier (SiPM) element readout for efficient and precise energy, time, and position measurements. Each channel incorporates an FPGA-based sigma-delta analog-to-digital converter (ΣΔ-ADC) and tapped delay line (TDL) based time-to-digital converter (TDC) for timing and energy estimation. Performance characterization of the system was performed through simulation, electronically generated waveform, and actual PET detector signals from three different single scintillation crystals of face dimensions 3 × 3 mm2 and depths of 5 and 20 mm coupled to a 3 × 3 mm2 SiPM. We also constructed and tested a modular PET detector with a 10x10 array of 1.2x1.2x14 mm³ LSO crystals coupled to a 4x4 SiPM array of 3 × 3 mm2 elements. Best energy resolution was 9.3% at the 511 KeV photopeak and best coincidence timing resolution (CTR) was 210 ± 3.5 ps. Our system balances cost-effectiveness with performance and contributes to developments in PET signal acquisition and detector technology.

Optical crosstalk of protective cover on MPPC array for TOF PET detector

Objective. Time-of-flight (TOF) is an important factor that directly affects the image quality of PET systems, and various attempts have been made to improve the coincidence resolving time (CRT) of PET detectors. For independent readout detectors, the timing is acquired for each silicon photomultiplier (SiPM), so they are less sensitive to diffused scintillation light, resulting in a better CRT. Further improvement can be expected if the light can be focused on a single SiPM. However, existing SiPM arrays have a thin protective cover on the SiPM and the gap between the SiPMs is filled with either air or the protective cover, so the light must diffuse through the cover. In this work, we investigated optical crosstalk in the protective cover to improve the CRT. Approach. We used 3.1 × 3.1 × 20 mm3 fast LGSO crystals and 3 mm square 8 × 8 multi pixel photon counter (MPPC) arrays. Pitch of the MPPCs was 3.2 mm and thickness of the protective cover on them was 150 μm. To reduce diffusion of scintillation light in the protective cover, the part of the inactive areas on the MPPC array were optically separated using reflective material. Specifically, 50, 100, 150, and 350 μm deep grid-shaped slits were made along the inactive area of the MPPCs and they were filled with BaSO4 powder as the reflective material. Main results. Coincidence counts were measured with a pair of TOF detectors, and the CRT was shorter with a deeper slit depth. The CRT before improvement was 235 ps, and using the cover having the 350 μm deep slits filled with reflective material lowered the CRT to 211 ps. Significance. Up to 10% of the scintillation light was diffused to other MPPCs by the protective cover, and the CRT was degraded by 10% due to optical crosstalk of the cover. The proposed method promises to improve the CRT of the TOF detector.

Dual threshold input receiver FPGA-only signal digitization method for time-of-flight positron emission tomography

As silicon photomultiplier (SiPM)-based time-of-flight (TOF) positron emission tomography (PET) becomes popular, the need for sophisticated PET data acquisition (DAQ) systems is increasing. One promising solution to this challenge is the adoption of a field-programmable gate array (FPGA)-only signal digitization method. In this paper, we propose a new approach to efficiently implement an FPGA-only digitizer. We configured the input/output (IO) port of the FPGA to function as a dual-threshold voltage comparator through the use of simple passive circuitry and heterogeneous IO standards. This configuration overcomes the limitations of existing methods by allowing different threshold voltages for adjacent IO pins, effectively reducing routing complexity and lowering manufacturing costs. An FPGA-only digitizer was implemented by integrating the dual-threshold voltage comparator and FPGA-based time-to-digital converter. By combining the dual-threshold time-over-threshold (TOT) method and curve fitting, precise energy information could be obtained. The performance of the FPGA-only digitizer was assessed using a detector setup comprising a 3 × 3 × 20 mm3 LYSO scintillation crystal and a single pixel SiPM. Using the configured evaluation setup, an energy resolution of 12.5% and a time resolution of 146 ± 9 ps were achieved for a 20 mm scintillation crystal. The dual-threshold TOT implemented using the proposed method showed consistent linearity across an energy range of 100 keV to 600 keV. The proposed method is well-suited for the development of cost-effective DAQ systems in highly integrated TOF PET systems.

Demonstration of particle tracking with scintillating fibres read out by a SPAD array sensor and application as a neutrino active target

Scintillating fibre detectors combine sub-mm resolution particle tracking, precise measurements of the particle stopping power and sub-ns time resolution. Typically, fibres are read out with silicon photomultipliers (SiPM). Hence, if fibres with a few hundred μ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\upmu $$\\end{document}m diameter are used, either they are grouped together and coupled with a single SiPM, losing spatial resolution, or a very large number of electronic channels is required. In this article we propose and provide a first demonstration of a novel configuration which allows each individual scintillating fibre to be read out regardless of the size of its diameter, by imaging them with Single-Photon Avalanche Diode (SPAD) array sensors. Differently from SiPMs, SPAD array sensors provide single-photon detection with single-pixel spatial resolution. In addition, O(us) or faster coincidence of detected photons allows to obtain noise-free images. Such a concept can be particularly advantageous if adopted as a neutrino active target, where scintillating fibres alternated along orthogonal directions can provide isotropic, high-resolution tracking in a dense material and reconstruct the kinematics of low-momentum protons (down to 150 MeV/c), crucial for an accurate characterisation of the neutrino-nucleus cross section. In this work the tracking capabilities of a bundle of scintillating fibres coupled to SwissSPAD2 is demonstrated. The impact of such detector configuration in GeV-neutrino experiments is studied with simulations and reported. Finally, future plans, including the development of a new SPAD array sensor optimised for neutrino detection, are discussed.

Photo-Trap: A low-cost and low-noise large-area SiPM-based pixel

The small sensitive area of commercial silicon photomultipliers (SiPMs) is often the main limitation for their use in experiments and applications that require large detection areas. Since capacitance, dark count rate and cost increase with the SiPM size, they are rarely found in sizes larger than 6 × 6 mm2. Photo-Trap combines a wavelength-shifter plastic, a dichroic filter and a standard commercial SiPM to build pixels of a few cm2. With this approach it can collect light over an area that can be ∼10–100 times larger than the area of a commercial SiPM, while keeping the noise, single-photoelectron resolution, power consumption and likely the cost of a single small SiPM. We developed four different proof-of concept pixels sensitive in the near UV band, the largest one being of 40 × 40 mm2. We characterized them through laboratory measurements and Geant4 simulations. The optical gain we measured with the prototypes went from ∼5 to ∼15, while the single-photon time resolution was of ∼3–5 ns FWHM. With the achieved performance Photo-Trap could be a competitive low-cost alternative for applications that require photosensors with large collection areas and low noise, such as dark matter experiments and optical wireless communication.

Study on the application of SiPM to [formula omitted] ray and charged particle measurement using scintillation crystals

The characteristics of a Silicon Photo Multiplier (SiPM)-based scintillation detector system were studied. The influence of the bias voltage and the number of SiPMs on the energy resolution was identified. The single SiPM energy spectra in the multi-SiPM system showed their dependency on the position of the 60Co radiation source. The application of geometric mean on the multi-SiPM system was also considered to bypass single channel calibrations.Preliminary results on the performances of developing scintillation detectors with a CsI(Tl) crystal or a plastic scintillator are demonstrated. The capability of charged particle measurement for CsI(Tl) crystal and sub-nanosecond timing resolution of plastic scintillator were identified.

The single-layer readout electronics design and development for CEPC scintillator analog hadronic calorimeter prototype

With the progress in modern high-energy physics, the Standard Model is constantly being refined. As the last brick of the Standard Model, the Higgs boson was confirmed to be discovered in the Large Hadron Collider (LHC) in 2012. For the further exploration of the Higgs boson, the Circular Electron Positron Collider (CEPC) is proposed. The baseline detector concept of CEPC is guided by the particle flow principle. The Particle Flow Algorithm (PFA) reconstructs a list of low-level particles and associates every detector hit with these particles. The high granularity hadronic calorimeter (HCAL) represents an essential component of PFA-based detectors. This paper mainly presents the single-layer electronics design and development for the scintillator analog hadronic calorimeter prototype (AHCAL). The single-layer readout electronics consists of front-end electronics board (FEB) and data interface (DIF) board. The FEB carries the silicon photomultipliers (SiPM), plastic scintillators, and the SiPM signal readout circuit. A single SiPM coupled with a scintillator constitute the basic detection unit. The size of scintillator used here is 4 cm×4 cm. A sensitive area of 72×72 cm2 can be covered by the design presented here. 324 SiPMs coupled with scintillators are mounted on each FEB. Besides the huge sensitive area, The AHCAL prototype must also meet strict requirements on the integration and robustness of the electronics. This paper develops a complete single-layer readout electronics design that meets the requirements for use in the AHCAL. The results of beam test shows that the peak of the minimum ionizing particle (MIP) is separated from the pedestal evidently and the signal-to-noise ratio (SNR) is better than 20. The volume required for the electronics is less than 4 cm3 per channel. In addition, the FEB is sufficiently robust to avoid damage during intercontinental transportation. The development of the single-layer electronics represents significant progress in the design of a prototype device that meets the requirement for use in the CEPC.

Evaluation of a resistor-chain-based SiPM detector for positron annihilation lifetime measurement

Silicon photomultipliers (SiPMs) have great potential to replace photomultiplier tubes (PMTs) and exceed their performance in positron annihilation parameter-measurement systems. However, due to the limited active area of a single SiPM, it only covers a small γ-ray emission acceptance range and provides position information over a very small region. Using a SiPM array is a good way to overcome these problems. In this study, a resistor-chain-based SiPM detector was designed and evaluated for positron annihilation lifetime (PAL) measurements. This detector uses a 1 × 4 scintillator array, a 1 × 4 SiPM array, and a resistor-chain readout circuit to obtain position, energy, and timing information about 1275 and 511 keV γ-rays, with the readout pulses serving as both the position, energy, and timing signals. A comprehensive evaluation was conducted to assess the detector in terms of position profile, energy resolution, and time resolution. The position profiles showed that all the crystal elements in the lutetium fine silicate scintillator array were clearly resolved. The detector had an energy resolution of 11.3±0.9% and a time resolution of 198±9 ps. A total of 32 PAL spectra were obtained using two SiPM array detectors. The PAL in yttria-stabilized zirconia (YSZ) sample was accurately verified using the summed PAL spectrum. The developed SiPM detector provides good performance for PAL measurements and could be used to build a high-performance PAL spectrometer.

Pulse-Shape Discrimination of 3-in Size NaI:Tl,⁶Li Scintillator Coupled With SiPM Array

Single crystals of NaI:Tl,6Li, a newly developed neutron-gamma scintillator, have satisfactory <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$n/\gamma $ </tex-math></inline-formula> discrimination capability and ease of scaling up. Using a silicon photomultiplier (SiPM) instead of a photomultiplier tube (PMT) as a readout for detector miniaturization has attracted considerable attention. Herein, we systematically compare the gamma spectroscopy and n/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\gamma $ </tex-math></inline-formula> discrimination performance of a 3-in NaI:Tl,6Li single crystal using R6233-100 PMT and two types of SiPM arrays as readouts. Using the PMT as a readout, a satisfactory energy resolution of 8.6% at 662 keV and an excellent figure of merit (FoM) of 4.36 at 1-GHz sampling rate can be achieved. Using the two types of SiPM arrays as readouts, the detectors have good linearity with energy resolutions of 14.4% and 10.6% at 662 keV and FoM values greater than 3- at 1-GHz sampling rate. Notably, at low sampling rates, the detector based on a 3-in NaI:Tl,6Li single crystal and SiPM array can maintain a very beneficial pulse-shape discrimination (PSD) performance, such as an FoM value of up to 2.73 at a sampling rate of 20 MHz.

Measurement of angular correlations of Compton-scattered gamma quanta from positron annihilation using GAGG:Ce scintillator matrices with single-side readout

We measured azimuthal correlations of the Compton-scattered gamma quanta from positron annihilation with two 8 × 8 matrices of Gadolinium Aluminum Gallium Garnet doped with Cerium. Each detector matrix contains 64 crystals of size 3 mm × 3 mm × 20 mm and it is read-out by a single Silicon Photo-multiplier (SiPM) array, with one SiPM matching one pixel. The studied single-side readout concept keeps the modules compact and cost-efficient on a large scale. Coincidence events were recorded using a Na-22 source placed between the modules. We clearly identify and reconstruct the Compton scattering events and we observe the excess of orthogonally scattered gammas over the ones with the parallel azimuthal angles. We present the measured azimuthal modulation factors for several kinematic selection criteria and different inter-pixel distances.

Evaluation of a clinical TOF-PET detector design that achieves ⩽100 ps coincidence time resolution

Commercially available clinical positron emission tomography (PET) detectors employ scintillation crystals that are long (20 mm length) and narrow (4–5 mm width) optically coupled on their narrow end to a photosensor. The aspect ratio of this traditional crystal rod configuration and 511 keV photon attenuation properties yield significant variances in scintillation light collection efficiency and transit time to the photodetector, due to variations in the 511 keV photon interaction depth in the crystal. These variances contribute significant to coincidence time resolution degradation. If instead, crystals are coupled to a photosensor on their long side, near-complete light collection efficiency can be achieved, and scintillation photon transit time jitter is reduced. In this work, we compare the achievable coincidence time resolution (CTR) of LGSO:Ce(0.025 mol%) crystals 3–20 mm in length when optically coupled to silicon photomultipliers (SiPMs) on either their short end or long side face. In this ‘side readout’ configuration, a CTR of 102 ± 2 ps FWHM was measured with mm3 crystals coupled to rows of mm2 SensL-J SiPMs using leading edge time pickoff and a single timing channel. This is in contrast to a CTR of 137 ± 3 ps FWHM when the same crystals were coupled to single mm2 SiPMs on their narrow ends. We further study the statistical limit on CTR using side readout via the Cramér–Rao lower bound (CRLB), with consideration given to ongoing work to further improve photosensor technologies and exploit fast phenomena to ultimately achieve 10 ps FWHM CTR. Potential design aspects of scalable front-end signal processing readout electronics using this side readout configuration are discussed. Altogether, we demonstrate that the side readout configuration offers an immediate solution for 100 ps CTR clinical PET detectors and mitigates factors prohibiting future efforts to achieve 10 ps FWHM CTR.

Impact of event positioning algorithm on performance of a whole-body PET scanner using one-to-one coupled detectors

The advent of silicon photomultipliers (SiPMs) has introduced the possibility of increased detector performance in commercial whole-body PET scanners. The primary advantage of these photodetectors is the ability to couple a single SiPM channel directly to a single pixel of PET scintillator that is typically 4 mm wide (one-to-one coupled detector design). We performed simulation studies to evaluate the impact of three different event positioning algorithms in such detectors: (i) a weighted energy centroid positioning (Anger logic), (ii) identifying the crystal with maximum energy deposition (1st max crystal), and (iii) identifying the crystal with the second highest energy deposition (2nd max crystal). Detector simulations performed with LSO crystals indicate reduced positioning errors when using the 2nd max crystal positioning algorithm. These studies are performed over a range of crystal cross-sections varying from 1 × 1 mm2 to 4 × 4 mm2 as well as crystal thickness of 1 cm to 3 cm. System simulations were performed for a whole-body PET scanner (85 cm ring diameter) with a long axial FOV (70 cm long) and show an improvement in reconstructed spatial resolution for a point source when using the 2nd max crystal positioning algorithm. Finally, we observe a 30–40% gain in contrast recovery coefficient values for 1 and 0.5 cm diameter spheres when using the 2nd max crystal positioning algorithm compared to the 1st max crystal positioning algorithm. These results show that there is an advantage to implementing the 2nd max crystal positioning algorithm in a new generation of PET scanners using one-to-one coupled detector design with lutetium based crystals, including LSO, LYSO or scintillators that have similar density and effective atomic number as LSO.

Pulse Shape Analysis and Discrimination for Silicon-Photomultipliers in Helium-4 Gas Scintillation Neutron Detector

Using natural helium (helium-4), the Arktis 180-bar pressurized gas scintillator is capable of detecting and distinguishing fast neutrons and gammas. The detector has a unique design of three optically separated segments in which 12 silicon-photomultiplier (SiPM) pairs are positioned equilaterally across the detector to allow for them to be fully immersed in the helium-4 gas volume; consequently, no additional optical interfaces are necessary. The SiPM signals were amplified, shaped, and readout by an analog board; a 250 MHz, 14-bit digitizer was used to examine the output pulses from each SiPMpair channel. The SiPM over-voltage had to be adjusted in order to reduce pulse clipping and negative overshoot, which was observed for events with high scintillation production. Pulse shaped discrimination (PSD) was conducted by evaluating three different parameters: time over threshold (TOT), pulse amplitude, and pulse integral. In order to differentiate high and low energy events, a 30ns gate window was implemented to group pulses from two SiPM channels or more for the calculation of TOT. It was demonstrated that pulses from a single SiPM channel within the 30ns window corresponded to low-energy gamma events while groups of pulses from two-channels or more were most likely neutron events. Due to gamma pulses having lower pulse amplitude, the percentage of measured gamma also depends on the threshold value in TOT calculations. Similarly, the threshold values were varied for the optimal PSD methods of using pulse amplitude and pulse area parameters. Helium-4 detectors equipped with SiPMs are excellent for in-the-field radiation measurement of nuclear spent fuel casks. With optimized PSD methods, the goal of developing a fuel cask content monitoring and inspection system based on these helium-4 detectors will be achieved.

Depth of interaction determination in monolithic scintillator with double side SiPM readout

BackgroundMonolithic scintillators read out by arrays of photodetectors represent a promising solution to obtain high spatial resolution and the depth of interaction (DOI) of the annihilation photon. We have recently investigated a detector geometry composed of a monolithic scintillator readout on two sides by silicon photomultiplier (SiPM) arrays, and we have proposed two parameters for the DOI determination: the difference in the number of triggered SiPMs on the two sides of the detector and the difference in the maximum collected signal on a single SiPM on each side. This work is focused on the DOI calibration and on the determination of the capability of our detector. For the DOI calibration, we studied a method which can be implemented also in detectors mounted in a full PET scanner. We used a PET detector module composed of a monolithic 20 × 20 × 10 mm3 LYSO scintillator crystal coupled on two opposite faces to two arrays of SiPMs. On each side, the scintillator was coupled to 6 × 6 SiPMs. In this paper, the two parameters previously proposed for the DOI determination were calibrated with two different methods. The first used a lateral scan of the detector with a collimated 511 keV pencil beam at steps of 0.5 mm to study the detector DOI capability, while the second used the background radiation of the 176Lu in the scintillator. The DOI determination capability was tested on different regions of the detector using each parameter and the combination of the two.ResultsWith both parameters for the DOI determination, in the lateral scan, the bias between the mean reconstructed DOI and the real beam position was lower than 0.3 mm, and the DOI distribution had a standard deviation of about 1.5 mm. When using the calibration with the radioactivity of the LYSO, the mean bias increased of about 0.2 mm but with no degradation of the standard deviation of the DOI distribution.ConclusionsThe two parameters allow to achieve a DOI resolution comparable with the state of the art, giving a continuous information about the three-dimensional interaction position of the scintillation. These results were obtained by using simple estimators and a detector scalable to a whole PET system. The DOI calibration obtained using lutetium natural radioactivity gives results comparable to the other standard method but appears more readily applicable to detectors mounted in a full PET scanner.

Towards the development of a SiPM-based camera for the Cherenkov Telescope Array

The Italian National Institute for Nuclear Physics (INFN) is involved in the development of a prototype for a camera based on Silicon Photomultipliers (SiPMs) for the Cherenkov Telescope Array (CTA), a new generation of telescopes for ground-based gamma-ray astronomy. In this framework, an R&D program within the ‘Progetto Premiale TElescopi CHErenkov made in Italy (TECHE.it)’ for the development of SiPMs suitable for Cherenkov light detection in the Near-Ultraviolet (NUV) has been carried out. The developed device is a NUV High-Density (NUV-HD) SiPM based on a micro cell of 30 μ m × 30 μ m and an area of 6 mm × 6 mm, produced by Fondazione Bruno Kessler (FBK). A full characterization of the single NUV-HD SiPM will be presented. A matrix of 8 × 8 single NUV-HD SiPMs will be part of the focal plane of the Schwarzschild- Couder Telescope prototype (pSCT) for CTA. An update on recent tests on the detectors arranged in this matrix configuration and on the front-end electronics will be given.

Study of the photo-detection efficiency of FBK High-Density silicon photomultipliers

This work presents a study of the factors contributing to the Photo-Detection Efficiency of Silicon Photomultipliers (SiPMs): Quantum Efficiency, Triggering Probability and Fill Factor. Two different SiPM High-Density technologies are tested, NUV-HD, based on n-on-p junction, and RGB-HD, based on p-on-n junction, developed at FBK, Trento. The quantum efficiency was measured on photodiodes produced along with the SiPMs. The triggering probability, as a function of wavelength and bias voltage, was measured on circular Single Photon Avalanche Diodes (SPADs) with 100% fill factor. Square SPADs, having the same layout of single SiPM cells, were studied to measure the effective fill factor and compare it to the nominal value. The comparison of the circular and square SPADs allows to get the transition region size between the effective active area of the cell and the one defined by the layout.

Set-up and methods for SiPM Photo-Detection Efficiency measurements

In this work, a compact set-up and three different methods to measure the Photo-Detection Efficiency (PDE) of Silicon Photomultipliers (SiPMs) and Single-Photon Avalanche Diodes (SPADs) are presented. The methods, based on either continuous or pulsed light illumination, are discussed in detail and compared in terms of measurement precision and time. For the SiPM, these methods have the feature of minimizing the effect of both the primary and correlated noise on the PDE estimation. The PDE of SiPMs (produced at FBK, Trento, Italy) was measured in a range from UV to NIR, obtaining similar results with all the methods. Furthermore, the advantages of measuring, when possible, the PDE of SPADs (of the same technology and with the same layout of a single SiPM cell) instead of larger devices are also discussed and a direct comparison between measurement results is shown. Using a SPAD, it is possible to reduce the measurement complexity and uncertainty since the correlated noise sources are reduced with respect to the SiPM case.

Scintillating fiber detectors for precise time and position measurements read out with Si-PMs

We present the development and performance of compact scintillating fiber detectors read out with silicon photo-multipliers (Si-PMs). The compact size, fast response, and insensitivity to magnetic fields make these detectors suitable for a variety of applications where precise tracking and timing information is required. These detectors will be used with different particle beams (electrons, protons, heavy ions) at very high rates. In particular, we present the SciFi tracker/time of flight detector that is being developed for the Mu3e experiment at PSI (search for the lepton flavor violating decay μ→eee at very high rates). We also present the SciFi beam position detectors that will be employed in NA61 at CERN to track the incoming proton and heavy ion beam particles. We are considering different readout scenarios in which (a) each fiber is individually coupled to a single Si-PM photo-sensor and (b) fibers are arranged in columns and coupled to a Si-PM arrays.

Design and optimization of a high-resolution PET detector module for small-animal PET based on a 12 × 12 silicon photomultiplier array

A high resolution PET detector module was designed and optimized based on a custom 12 × 12 Silicon photomultiplier (SiPM) array and commercially available readout electronics (SensL Ltd., Ireland). The total area of this SiPM array is 50.2 mm × 50.2 mm, and consists of 3 × 3 sections each containing 4 × 4 SiPM elements. Each SiPM, made using 35 um microcell technology, has a sensitive area of 3.0 mm × 3.0 mm in a 4.0 mm × 4.0 mm package and is fabricated into an array with 4.2 mm pitch. The performance of this detector was evaluated using 16 × 16 arrays of 0.975 mm × 0.975 mm × 12 mm polished LYSO crystals. Such small crystals make one-to-one coupling between the SiPM and LYSO crystal impractical. In this work, therefore, the detector was evaluated using light sharing approaches. Flood histogram quality, signal amplitude, and energy resolution were compared at different bias voltages (28.0–32.5 V in 0.5 V intervals) using five light guides with different thickness (from 0.8 mm to 2.0 mm) at a fixed temperature of 5 °C by coupling the LYSO array to a single SiPM section. The best flood histogram was obtained at a bias voltage of 29.5 V using the 1.0 mm thick light guide. Under these conditions, all the LYSO crystals can be clearly separated and the average energy resolution was 18.6 ± 1.9%. The timing resolution was 6.0 ± 0.1 ns after leading edge time walk correction, obtained by using two identical detectors consisting of two 12 × 12 SiPM arrays and two 16 × 16 LYSO arrays. The LYSO array was moved such that it was coupled to the center of four SiPM sections and all crystals could still be clearly resolved. These results show that a high-resolution small-animal PET scanner could be developed based on these large-area SiPM arrays and commercially available electronics.

감마선 분광분석을 위한 실리콘 광 증배소자 기반 Ce:GAGG 섬광검출기의 분광특성 연구

In this study, a scintillation detector was fabricated using a silicon photomultiplier (SiPM) and a Ce:GAGG scintillator single crystal, and its spectroscopic properties were compared with those of commercially available LYSO and CsI:Tl scintillators using -ray spectroscopy. The energy resolutions of the self-produced scintillation detector composed of the scintillator single crystal (volume: ) and SiPM (Photosensitive area: ) for standard -ray sources, such as , , and were measured and compared. As a result, the energy resolutions of the proposed Ce:GAGG scintillation detector for g-rays, as measured using its spectroscopic properties, were found to be 13.5% for 0.356 MeV, 6.9% for 0.511 MeV, 5.8% for 0.662 MeV and 2.3% for 1.33 MeV.