SiPM-based Scintillation Detectors Research Articles

Characterization of external optical crosstalk reduction for SiPM-based scintillation detectors with an optical bandpass filter

External optical crosstalk remains a significant source of correlated noise in scintillation detectors optically coupled to silicon photomultiplier (SiPM) arrays and can influence achievable performance by limiting the maximum overvoltage at which a detector can be operated. This study evaluated the potential benefits of incorporating an optical bandpass filter, which is absorptive to optical crosstalk and transmissive for scintillation photons, between the scintillator and SiPM array. Several SiPM and bandpass configurations were characterized, including single-element and SiPM arrays with bare, filter-coupled, crystal-coupled, and crystal-filter-coupled interfaces. Coupling the optical filter between a 4 × 4 array of Broadcom AFBR-S4N44P164 M (NUV-MT) SiPMs and a 12 × 12 × 20 mm3 LYSO crystal decreased the total number of detected optical photon noise by up to 92%. The impact of the filter on crosstalk probability reduction was also characterized by the single-channel measurements with the same SiPM, suppressing external crosstalk up to 64%. With the filter coupled, SiPMs were operable at very high overvoltage. The results of these studies demonstrate that optical filtering is a promising technique to significantly reduce correlated noise in scintillation detectors employing SiPMs.

X-ray spectroscopy with a photon-counting SiPM-based scintillation detector

A new low-energy X-ray detector was built and operated, using a plastic scintillator coupled to a large area SiPM.The signal is amplified with a low-noise, high gain, custom circuit providing excellent photon-counting capabilities and allowing a quasi-digital measurement.The detector was tested using X-rays coming from molybdenum K lines (17.4 and 19.6 keV), and an energy resolution of 28% is obtained with 20 photoelectrons per X-ray photon on average.

Dedicated SiPM array for GRD of GECAM

PurposeThe discovery of gravitational waves and gamma-ray bursts heralds the era of multi-messenger astronomy. With the adoption of two small satellites to achieve the all-sky monitoring of gamma-ray bursts, the gravitational wave high-energy electromagnetic counterpart all-sky monitor (GECAM) possesses a quasi-real-time early warning ability and plays an important role in positioning the sources of gravitational waves and in subsequent observations. Each satellite of GECAM was fitted with 25 3-inch-diameter gamma-ray detectors (GRD), covering an energy range of 8–2 MeV. GRDs have adopted silicon photomultiplier tubes (SiPM) in lieu of photomultiplier tubes (PMT) to adapt to the dimensional limitations of micro-satellites.MethodsA unique 3-inch circular SiPM array was designed. In this design, 64 6 × 6 mm chips were arranged evenly in a circular manner with the seams filled with reflecting films, thus achieving satisfactory uniformity of light collection. The integrated pre-amplifier circuit on the back of the SiPM array adopted two-level grouping and summing; further, it achieved a satisfactory signal-to-noise ratio. Two high-gain and low-gain channels were adopted to achieve a large dynamic range, and two independent power supply units were used, where each unit can be closed separately, thus improving reliability.ResultsPerformance studies show that this SiPM array meets the requirements of GECAM.ConclusionA 3-inch SiPM array have been developed that uses grouped summation, reflective films, a circular arrangement, two groups of independent power supplies, high- and low-gain signals, differential signal output technologies, etc. This solution can be used not only for GECAM, but also as a general solution for SiPM-based scintillation detectors.

A temperature-dependent gain compensation technique for positron emission tomography detectors based on a silicon photomultiplier

In this study, we propose a simple gain compensation technique for silicon photomultiplier (SiPM)-based positron emission tomography detectors, using a temperature sensor that automatically controls the bias voltage of the SiPM depending upon the ambient temperature. The temperature sensor output, for which the temperature coefficient can be controlled by the input voltage, is used as one end of the bias voltage. By adjusting the temperature coefficient, the proposed gain compensation method can be applied to various SiPMs with different breakdown voltages. As a proof of concept, the proposed method was evaluated for two scintillation detector setups. Applying the proposed method to a single-channel SiPM (ASD-NUV3S-P; AdvanSiD, Italy) coupled with a 3 mm × 3 mm × 20 mm LGSO crystal, the 511 keV photopeak position in the energy histogram changed by only 1.52% per 10 °C while, without gain compensation, it changed by 13.27% per 10 °C between 10 °C and 30 °C. On a 4 × 4 array MPPC (S14161-3050HS-04; Hamamatsu, Japan), coupled with a 3.12 mm × 3.12 mm × 15 mm 4 × 4 LSO array, the photopeak changes with and without gain compensation were 2.34% and 20.53% per 10 °C between 10 °C and 30 °C, respectively. On the wider range of temperature, between 0 °C and 40 °C, the photopeak changes with and without gain compensation were 3.09% and 20.89%, respectively. The energy resolution degradation of SiPM-based scintillation detectors operating at temperatures was negligible when the proposed gain compensation method was applied.

Silicon photomultiplier-based scintillation detectors for photon-counting CT: A feasibility study.

PurposeThe implementation of photon‐counting detectors is widely expected to be the next breakthrough in X‐ray computed tomography (CT) instrumentation. A small number of prototype scanners equipped with direct‐conversion detectors based on room‐temperature semiconductors, such as CdTe and CdZnTe (CZT), are currently installed at medical centers. Here, we investigate the feasibility of using silicon photomultiplier (SiPM)‐based scintillation detectors in photon‐counting computed tomography (PCCT) scanners, as a potential alternative to CdTe and CZT detectors.MethodsWe introduce a model that allows us to compute the expected energy resolution as well as the expected pulse shape and associated rate capability of SiPM‐based PCCT detectors. The model takes into account SiPM saturation and optical crosstalk, because these phenomena may substantially affect the performance of SiPM‐based PCCT detectors with sub‐mm pixels. We present model validation experiments using a single‐pixel detector consisting of a 0.9 × 0.9 × 1.0 mm3 LuAP:Ce scintillation crystal coupled to a 1 × 1 mm2 SiPM. We subsequently use the validated model to compute the expected performance of the fast scintillators LYSO:Ce, LuAP:Ce, and LaBr3:Ce, coupled to currently available SiPMs, as well as to a more advanced SiPM prototype with improved dynamic range, for sub‐mm pixel sizes.ResultsThe model was found to be in good agreement with the validation experiments, both with respect to energy resolution and pulse shape. It shows how saturation progressively degrades the energy resolution of detectors equipped with currently available SiPMs as the pixel size decreases. Moreover, the expected pulse duration is relatively long (~200 ns) with these SiPMs. However, when LuAP:Ce and LaBr3:Ce are coupled to the more advanced SiPM prototype, the pulse duration improves to less than 60 ns, which is in the same order of magnitude as pulses from CdTe and CZT detectors. It follows that sufficient rate capability can be achieved with pixel sizes of 400 μm or smaller. Moreover, LaBr3:Ce detectors can provide an energy resolution of 11.5%‐13.5% at 60 keV, comparable to CdTe and CZT detectors.ConclusionsThis work provides first evidence that it may be feasible to develop SiPM‐based scintillation detectors for PCCT that can compete with CdTe and CZT detectors in terms of energy resolution and rate capability.

Multiple time-over-threshold readout electronics for fast timing and energy resolving in a SiPM-based positron annihilation lifetime spectrometer

Fast timing and energy resolving capabilities are crucial for a silicon-photomultiplier-based positron annihilation lifetime (SiPM-PAL) spectrometer. Time-over-threshold (ToT) offers an attractive method for combining timing and energy encoding with the advantage of simplicity in electronics implementation and SiPM readout. However, single ToT is not appropriate for a SiPM-PAL spectrometer because of its poor energy linearity and limited energy range. In this work, a multi-ToT readout circuit for a SiPM-PAL spectrometer is developed. Each readout channel uses only a pre-amplifier and a comparator for timing, three comparators for energy resolving, resistors, and capacitors. A simple pulse area estimation method using multi-ToT pulse widths and fixed threshold voltages for energy resolving is presented and evaluated. The energy performance and pulse area integral nonlinearity (INL) are investigated using 22Na, 60Co, and 137Cs γ sources with a SiPM-based scintillation detector. For pulse area spectra using the proposed method, multi-ToT (triple and dual threshold cases) resolves γ energies much better than does single ToT. Using triple-ToT, the pulse area linearity in INL in the energy range of 511–1333 keV is superior than 4.21%, which is at least 25% better than that with dual-ToT. Excellent coincidence resolving times of 161.5 ± 1.4 ps and 162.7 ± 1.3 ps in full width at half maximum are achieved using triple-ToT and dual-ToT, respectively, for 3 mm\\;×\\;3 mm\\;×\\;5 mm lutetium-fine-silicate scintillators. The quantitative energy and timing results show that the multi-ToT circuit is suitable for the readout electronics of a SiPM-PAL spectrometer.

Feasibility study of SiPM based scintillation detector for dual-energy X-ray absorptiometry

Dual-energy x-ray absorptiometry (DXA) is the noninvasive method to diagnose osteoporosis disease characterized by low bone mass and deterioration of bone tissue. Many global companies and research groups have developed the various DXA detectors using a direct photon-counting detector such as a cadmium zinc telluride (CZT) sensor. However, this approach using CZT sensor has some drawback such as the limitation of scalability by high cost and the loss of efficiency due to the requirement of a thin detector.In this study, a SiPM based DXA system was developed and its performance evaluated experimentally. The DXA detector was composed of a SiPM sensor coupled with a single LYSO scintillation crystal (3 × 3 × 2 mm3). The prototype DXA detector was mounted on the dedicated front-end circuit consisting of a voltage-sensitive preamplifier, pulse shaping amplifier and constant fraction discriminator (CFD) circuit. The SiPM based DXA detector showed the 34% (at 59 keV) energy resolution with good BMD accuracy. The proposed SiPM based DXA detector showed the performance comparable to the conventional DXA detector based on CZT.

A new SiPM-based positron annihilation lifetime spectrometer using LYSO and LFS-3 scintillators

Positron annihilation lifetime (PAL) spectroscopy is a unique technique to characterize atomic-scaled microstructure of materials, especially the vacancy-type defects. Compared to photomultiplier tube, silicon photomultiplier (SiPM) has a higher quantum efficiency, a more compact size, and a much lower price. Considering the evident advantages of SiPM, we developed a SiPM-based PAL (SiPM-PAL) spectrometer by using LFS-3 and LYSO scintillators in the sizes of 3×3×l mm3. The performance of the SiPM-PAL spectrometer was studied with four different scintillator lengths (l) of 5.0, 9.5, 13.8, and 20.0 mm. Under the same experimental conditions, with LFS-3 scintillator length decreasing from 20.0 to 5.0 mm, the time resolution (in FWHM) of SiPM-PAL spectrometer was significantly improved from 174.9 to 135.9 ps. While for the SiPM-PAL spectrometer with LYSO scintillators, the time resolution improved from 181.9 to 137.0 ps with scintillator length decreasing from 20.0 to 5.0 mm. Compared to conventional PAL spectrometer using photomultiplier tubes, a novel, small size, and low cost PAL spectrometer is successfully constructed by using SiPMs. Easy customization and superiority in time resolution and small size of SiPM-based scintillation detectors guarantee high flexibility and adaptability to the SiPM-PAL spectrometers, positron micro-beam facilities, and angular correlation of positron annihilation radiation measurements.

Efficient design of a ∅2×2 inch NaI(Tl) scintillation detector coupled with a SiPM in an aquatic environment

Abstract After the Fukushima accident in 2011, there has been increased public concern about radioactive contamination of water resources through fallout in neighboring countries. However, there is still no available initial response system that can promptly detect radionuclides. The purpose of this research is to develop the most efficient gamma spectrometer to monitor radionuclides in an aquatic environment. We chose a thallium-doped sodium iodide (NaI(Tl)) scintillator readout with a silicon photo multiplier (SiPM) due to its compactness and low operating voltage. Three types of a scintillation detector were tested. One was composed of a scintillator and a photomultiplier tube (PMT) as a reference; another system consisted of a scintillator and an array of SiPMs with a light guide; and the other was a scintillator directly coupled with an array of SiPMs. Among the SiPM-based detectors, the direct coupling system showed the best energy resolution at all energy peaks. It achieved 9.76% energy resolution for a 662 keV gamma ray. Through additional experiments and a simulation, we proved that the light guide degraded energy resolution with increasing statistical uncertainty. The results indicated that the SiPM-based scintillation detector with no light guide is the most efficient design for monitoring radionuclides in an aquatic environment.

Study of [formula omitted]-[formula omitted] discrimination by zero-crossing method with SiPM based scintillation detectors

The paper presents a study of n∕γ discrimination with 4x4 ch and 8x8 ch Multi Pixel Photon Counter (MPPC) arrays in neutron detectors based on Stilbene and EJ299-33 plastic scintillators. The n∕γ discrimination showed an excellent capability of the MPPC arrays, comparable to that observed earlier with the classical PMTs. Particularly, an application of a zero-crossing method of n−γ discrimination prevented deterioration of the discrimination by the slow response of the Silicon Photomultiplier (SiPM, or MPPC interchangeably) array related to its large capacitance. It was confirmed by a good agreement of the Figure of Merit normalized to the number of photoelectrons determined for the MPPC arrays and XP5500 PMT.

Measurement of the time resolution of small SiPM-based scintillation counters

In this research, we evaluated the timing resolution of SiPM-based scintillation detector on a 1-GeV electron beam “extracted” from VEPP-4M. We tested small scintillation crystals of pure CsI, YAP, LYSO, and LFS-3 with HAMAMATSU S10362-33-025C and S13360-3050CS. The CsI scintillator together with HAMAMATSU S13360-3050CS demonstrated the best results. Nevertheless, the achieved time resolution of ∼80 ps (RMS) relates mainly to the photodetector itself. It makes the silicon photomultiplier an attractive candidate to replace other devices in applications where sub-nanosecond accuracy is required.

Digital Signal Processing for SiPM Timing Resolution

Digital signal processing (DSP) is an emerging trend in experimental studies and applications of various detectors including SiPMs. In particular, the DSP is recognized as a promising approach to improve coincidence timing resolution (CTR) of fast SiPM-based scintillation detectors. Single photon timing resolution (SPTR) is one of the key parameters affecting CTR, especially important in a case when CTR is approaching to its ultimate limits as, for example, highly demanded in Time-of-Flight PET. To study SiPM timing resolution, we developed a special DSP software and applied it to both SPTR and CTR measurements. These measurements were carried out using 3x3 mm2 KETEK SiPM samples of timing optimized and standard designs with 405 nm picosecond laser for SPTR and with 3x3x5 mm3 LYSO crystals and 511 keV Na-22 source for CRT. Results of the study are useful for further improvements of DSP algorithms and SiPM designs for fast timing.

Performance characteristics of a silicon photomultiplier based compact radiation detector for Homeland Security applications

A next-generation compact radiation detector was studied for more accurate measurement of radiation and for improvement of detector reliability for the purpose of developing radiation protection technology and military applications. The previously used radiation detector had some limitations due to its bulky size, limited range and its environment for radiation measurement. On the other hand, the compact radiation detector examined in this study utilizes a silicon photomultiplier which appears to be more suitable for this application because of its physical superiority characterized by its small size, high sensitivity, and durability. Accordingly, a SiPM based scintillation detector has been developed as part of this basic study of military radiation detectors. The detector has been tested for its ability to obtain the operating characteristics of a sensor and analyzed with variations of parameter values and for efficiency of detection in accordance with its ability to measure radiation in the environment. Two SiPM based Scintillation detectors with LYSO, BGO and CsI:Tl scintillators were developed and the detectors were analyzed by a number of operating characteristics such as reverse bias, operating temperature and high magnetic field, that depend on environmental changes in radiation measurement. The Photon count rate and spectra were compared for these three scintillators. We found that there were variations in the radiation detection which were characterized by reverse bias, temperature and high magnetic field. It was also found that there was an 11.9% energy resolution for the LYSO, 15.5% for BGO and 13.5% for CsI:Tl using Array SiPM, and 18% for CsI:Tl energy resolution using single SiPM when we measured energy resolution of 511keV for 22Na. These results demonstrate the potential widespread use of SiPM based compact radiation detectors for Homeland Security applications.

Simulating Silicon Photomultiplier Response to Scintillation Light.

The response of a Silicon Photomultiplier (SiPM) to optical signals is affected by many factors including photon-detection efficiency, recovery time, gain, optical crosstalk, afterpulsing, dark count, and detector dead time. Many of these parameters vary with overvoltage and temperature. When used to detect scintillation light, there is a complicated non-linear relationship between the incident light and the response of the SiPM. In this paper, we propose a combined discrete-time discrete-event Monte Carlo (MC) model to simulate SiPM response to scintillation light pulses. Our MC model accounts for all relevant aspects of the SiPM response, some of which were not accounted for in the previous models. We also derive and validate analytic expressions for the single-photoelectron response of the SiPM and the voltage drop across the quenching resistance in the SiPM microcell. These analytic expressions consider the effect of all the circuit elements in the SiPM and accurately simulate the time-variation in overvoltage across the microcells of the SiPM. Consequently, our MC model is able to incorporate the variation of the different SiPM parameters with varying overvoltage. The MC model is compared with measurements on SiPM-based scintillation detectors and with some cases for which the response is known a priori. The model is also used to study the variation in SiPM behavior with SiPM-circuit parameter variations and to predict the response of a SiPM-based detector to various scintillators.

A Comprehensive Model to Predict the Timing Resolution of SiPM-Based Scintillation Detectors: Theory and Experimental Validation

Silicon photomultipliers (SiPMs) are expected to replace photomultiplier tubes (PMTs) in several applications that require scintillation detectors with excellent timing resolution, such as time-of-flight positron emission tomography (TOF-PET). However, the theory about the timing resolution of SiPM-based detectors is not yet fully understood. Here we propose a comprehensive statistical model to predict the timing resolution of SiPM-based scintillation detectors. It incorporates the relevant SiPM-related parameters (viz. the single cell electronic response, the single cell gain, the charge carrier transit time spread, and crosstalk) as well as the scintillation pulse rise and decay times, light yield, and energy resolution. It is shown that the proposed model reduces to the well-established Hyman model for timing with PMTs if the number of primary triggers (photoelectrons in case of a PMT) is Poisson distributed and crosstalk and electronic noise are negligible. The model predictions are validated by measurements of the coincidence resolving times (CRT) for 511 keV photons of two identical detectors as a function of SiPM bias voltage, for two different kinds of scintillators, namely LYSO:Ce and LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> :5%Ce. CRTs as low as 138 ps ± 2 ps FWHM for LYSO:Ce and 95 ps ± 3 ps FWHM for LaBr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> :5%Ce were obtained, demonstrating the outstanding timing potential of SiPM-based scintillation detectors. These values were found to be in good agreement with the predicted CRTs of 140 ps FWHM and 95 ps FWHM, respectively. Utilizing the proposed model, it can be shown that the CRTs obtained in our experiments are mainly limited by photon statistics while crosstalk, electronic noise and signal bandwidth have relatively little influence.

Characterization and Optimization of silicon photomultipliers for the development of intraoperative beta probes

This work reports the results of a comprehensive study aiming to characterize and optimize the performances of Silicon Photomultipliers (SiPM) as photodetectors for intraoperative beta detection of radiolabeled tumor tissues. In that purpose, we focused our measurements on the influence of temperature and operating voltage on dark noise (count rate and amplitude distribution), absolute photon detection efficiency and total gain of different SiPM devices from Hamamatsu. The impact of these parameters on the overall beta sensitivity of SiPM-based scintillation detectors was quantified as a function of the intensity of the incident light following a simple physical model that is shown to correspond well with measurements.

A Comprehensive Model of the Response of Silicon Photomultipliers

The response of a silicon photomultiplier (SiPM) to optical signals is inherently nonproportional due to saturation, afterpulsing, and crosstalk. Existing models of the SiPM response do not account for all of these effects, and therefore, these models are not sufficiently accurate for many applications. In this work, a comprehensive model of the SiPM response is developed that is generally applicable to exponentially decaying light pulses and that can be simplified in the case of very short (e.g., laser) light pulses. The model accounts for the total number and the temporal distribution of the incident photons as well as for the relevant SiPM parameters, viz. the recovery time, afterpulsing, crosstalk, and their cross correlations. The model is shown to correspond well with measurements on a SiPM-based scintillation detector. Furthermore, it is shown to be in agreement with several cases for which the SiPM response is known <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">a priori</i> . Having thus validated the model, its use is demonstrated by predicting the response of the Hamamatsu multipixel photon counter (MPPC) S10362-33-050C SiPM to several different scintillators.

LaBr3:Ce and SiPMs for time-of-flight PET: achieving 100 ps coincidence resolving time

The use of time-of-flight (TOF) information in positron emission tomography (PET) enables significant improvement in image noise properties and, therefore, lesion detection. Silicon photomultipliers (SiPMs) are solid-state photosensors that have several advantages over photomultiplier tubes (PMTs). SiPMs are small, essentially transparent to 511 keV gamma rays and insensitive to magnetic fields. This enables novel detector designs aimed at e.g. compactness, high resolution, depth-of-interaction (DOI) correction and MRI compatibility. The goal of the present work is to study the timing performance of SiPMs in combination with LaBr3:Ce(5%), a relatively new scintillator with promising characteristics for TOF-PET. Measurements were performed with two, bare, 3 mm × 3 mm × 5 mm LaBr3:Ce(5%) crystals, each coupled to a 3 mm × 3 mm SiPM. Using a 22Na point source placed at various positions in between the two detectors, a coincidence resolving time (CRT) of ∼100 ps FWHM for 511 keV annihilation photon pairs was achieved, corresponding to a TOF positioning resolution of ∼15 mm FWHM. At the same time, pulse height spectra with well-resolved full-energy peaks were obtained. To our knowledge this is the best CRT reported for SiPM-based scintillation detectors to date. It is concluded that SiPM-based scintillation detectors can provide timing resolutions at least as good as detectors based on PMTs.