Silicon Photomultiplier Matrices Research Articles

Study of the thermal neutron activation of a gamma-ray detector for BNCT dose monitoring

We present a study on the neutron activation of a gamma-ray detector for a BNCT-SPECT dose imaging system. The detector is based on a LaBr3(Ce+Sr) scintillator crystal, coupled with a matrix of Silicon Photomultipliers (SiPMs), read by a dedicated electronics system. This detector has successfully demonstrated to be capable to identify the 10B compounds when irradiating borated vials with thermal neutrons. However, a background signal around 478 keV was detected, suggesting the activation of the detector itself. This study aims to determine the origin of this background signal by simulating the two main parts of the detector, which are the crystal and electronic boards, in order to assess their contribution to the background signal. The results of the FLUKA simulations show that the neutron capture reactions on both the crystal and electronic boards cause a relevant background nearby the BNCT signal, thereby limiting the detector's sensitivity. To address this issue, a customized cadmium shielding has been developed. This solution was tested at the TRIGA Mark II research nuclear reactor of Pavia University, where experimental measurements and corresponding FLUKA simulations proved its effectiveness.

Studying the Operation of Silicon Photomultiplier Matrices at Cryogenic Temperatures

Studying the Operation of Silicon Photomultiplier Matrices at Cryogenic Temperatures

Experimental validation of a spectroscopic gamma-ray detector based on a LaBr3 scintillator towards real-time dose monitoring in BNCT

We report the experimental validation of a detection module based on a LaBr3(Ce＋Sr) scintillator crystal, read by a matrix of Silicon Photomultipliers (SiPMs), for the development of a SPECT system for dose monitoring in Boron Neutron Capture Therapy (BNCT). The goal of the system is to detect the gamma rays at 478keV emitted by the excited 7Li produced in the 10B(n, α)7Li reaction, to have a real-time localization and quantification of the local dose released to a patient during BNCT treatment. The good energy resolution of the detector (<3% at 662keV) allows to resolve the photopeak at 478keV from the adjacent annihilation photons photopeak at 511keV, originated from pair production of high energy gamma rays, such as the hydrogen neutron capture gamma rays at 2.2MeV. The results shown in this article demonstrate the suitability of our detector in view of future application in BNCT real-time dose monitoring. Good linearity (RMSE < 2.5cps) between the number of events detected at 478keV and the boron concentration of the 10B-loaded samples has been achieved, down to a boron concentration of 62ppm with a neutron flux of approximately 1 × 105 n/cm2/s.

SiPM-matrix readout of two-phase argon detectors using electroluminescence in the visible and near infrared range

Proportional electroluminescence (EL) in noble gases is used in two-phase detectors for dark matter searches to record (in the gas phase) the ionization signal induced by particle scattering in the liquid phase. The “standard” EL mechanism is considered to be due to noble gas excimer emission in the vacuum ultraviolet (VUV). In addition, there are two alternative mechanisms, producing light in the visible and near infrared (NIR) ranges. The first is due to bremsstrahlung of electrons scattered on neutral atoms (“neutral bremsstrahlung”, NBrS). The second, responsible for electron avalanche scintillation in the NIR at higher electric fields, is due to transitions between excited atomic states. In this work, we have for the first time demonstrated two alternative techniques of the optical readout of two-phase argon detectors, in the visible and NIR range, using a silicon photomultiplier matrix and electroluminescence due to either neutral bremsstrahlung or avalanche scintillation. The amplitude yield and position resolution were measured for these readout techniques, which allowed to assess the detection threshold for electron and nuclear recoils in two-phase argon detectors for dark matter searches. To the best of our knowledge, this is the first practical application of the NBrS effect in detection science.

Russian-Azerbaijani space project of a small satellite for science and technology experiments

The paper presents a project of a satellite experiment on the observation of intense flashes (transients) of electromagnetic emission from the Earth's atmosphere in different spectral ranges, as well as the measurement of medium- and long-term dynamics of spatial distribution of fluxes of energetic charged particles in the near-Earth space. To implement the experiment, it is planned to develop a Russian-Azerbaijani small spacecraft capable of carrying a payload of up to 25-30 kg. The satellite is also expected to realize a number of technology experiments, in particular, to study the effect of space flight factors on the matrices of silicon photomultipliers. We also consider the possibility of installing a telescope for photometric observations of binary stars. The requirements to the orbit and spacecraft attitude modes, as well as to its on-board systems, are considered in accordance with the goals and objectives of the experiment. The measurement data which are planned to be obtained during this experiment will subsequently be used for various scientific and applied problems including validation of existing and development of new dynamic models of radiation in the near-Earth space, ensuring the safety of the functioning of spacecraft.

Development of the Scintillation Track Detector Based on Multichannel Photodetectors

Matrices of silicon photomultipliers (SiPM) are promising multichannel photosensors for scintillation detectors. They can be used to construct tracks of relativistic particles inside detectors. The first detectors based on the direct contact of the SiPM matrices with the surface of the scintillation detector and with the application of Fresnel lenses are developed; promising variants of large detectors for neutrino astrophysics and geophysics are proposed.

Development of a scintillation detector with a photosensor based on matrices of silicon photomultipliers

Scintillation detector with matrices of silicon photomultipliers (SiPM) as multi-channel photosensors is under development. The use of SiPM matrices gives a possibility to do a snapshot of glowing track of charged particle traversing a scintillator. The snapshots of the events inside the scintillator were taken for the two SiPM matrices arrangements. The comparison characteristics of snapshots for these arrangements are presented.

Development of a composite large-size SiPM (assembled matrix) based modular detector cluster for MAGIC

The MAGIC collaboration operates two 17m diameter Imaging Atmospheric Cherenkov Telescopes (IACTs) on the Canary Island of La Palma. Each of the two telescopes is currently equipped with a photomultiplier tube (PMT) based imaging camera. Due to the advances in the development of Silicon Photomultipliers (SiPMs), they are becoming a widely used alternative to PMTs in many research fields including gamma-ray astronomy. Within the Otto-Hahn group at the Max Planck Institute for Physics, Munich, we are developing a SiPM based detector module for a possible upgrade of the MAGIC cameras and also for future experiments as, e.g., the Large Size Telescopes (LST) of the Cherenkov Telescope Array (CTA). Because of the small size of individual SiPM sensors (6mm×6mm) with respect to the 1-inch diameter PMTs currently used in MAGIC, we use a custom-made matrix of SiPMs to cover the same detection area. We developed an electronic circuit to actively sum up and amplify the SiPM signals. Existing non-imaging hexagonal light concentrators (Winston cones) used in MAGIC have been modified for the angular acceptance of the SiPMs by using C++ based ray tracing simulations. The first prototype based detector module includes seven channels and was installed into the MAGIC camera in May 2015. We present the results of the first prototype and its performance as well as the status of the project and discuss its challenges.

Time resolution of the plastic scintillator strips with matrix photomultiplier readout for J-PET tomograph

Recent tests of a single module of the Jagiellonian Positron Emission Tomography system (J-PET) consisting of 30 cm long plastic scintillator strips have proven its applicability for the detection of annihilation quanta (0.511 MeV) with a coincidence resolving time (CRT) of 0.266 ns. The achieved resolution is almost by a factor of two better with respect to the current TOF-PET detectors and it can still be improved since, as it is shown in this article, the intrinsic limit of time resolution for the determination of time of the interaction of 0.511 MeV gamma quanta in plastic scintillators is much lower. As the major point of the article, a method allowing to record timestamps of several photons, at two ends of the scintillator strip, by means of matrix of silicon photomultipliers (SiPM) is introduced. As a result of simulations, conducted with the number of SiPM varying from 4 to 42, it is shown that the improvement of timing resolution saturates with the growing number of photomultipliers, and that the configuration at two ends allowing to read twenty timestamps, constitutes an optimal solution. The conducted simulations accounted for the emission time distribution, photon transport and absorption inside the scintillator, as well as quantum efficiency and transit time spread of photosensors, and were checked based on the experimental results. Application of the matrix of SiPM allows for achieving the coincidence resolving time in positron emission tomography of 0.170 ns for 15 cm axial field-of-view (AFOV) and 0.365 ns for 100 cm AFOV. The results open perspectives for construction of a cost-effective TOF-PET scanner with significantly better TOF resolution and larger AFOV with respect to the current TOF-PET modalities.

Performance of VATA64HDR16 ASIC for medical physics applications based on continuous crystals and SiPMs

Detectors based on Silicon Photomultipliers (SiPMs) coupled to continuous crystals are being tested in medical physics applications due to their potential high resolution and sensitivity. To cope with the high granularity required for a very good spatial resolution, SiPM matrices with a large amount of elements are needed. To be able to read the information coming from each individual channel, dedicated ASICs are employed. The VATA64HDR16 ASIC is a 64-channel, charge-sensitive amplifier that converts the collected charge into a proportional current or voltage signal. A complete assessment of the suitability of that ASIC for medical physics applications based on continuous crystals and SiPMs has been carried out. The input charge range is linear from 0−2 pC up to 55 pC. The energy resolution obtained at 511 keV is 10% FWHM with a LaBr3 crystal and 16% FWHM with a LYSO crystal. A coincidence timing resolution of 24 ns FWHM is obtained with two LYSO crystals.

Front-end chip for Silicon Photomultiplier detectors with pico-second Time-of-Flight resolution

A mixed-mode readout Application Specific Integrated Circuit (STIC3) has been developed for high precision timing measurements with Silicon Photomultipliers (SiPM) for medical imaging and particle physics applications. The STiC3 is a 64-channel chip, with fully differential analog front-end for cross-talk and electronic noise immunity. The time and charge information from the SiPM signals are encrypted into two time stamps generated by integrated Time to Digital Converter (TDC) modules with 50ps time binning. The TDC data is stored in an internal memory and transferred to a PC via a 160MBit/s serial link using an 8/10 bit encoding. The chip provides an input bias tuning in a range of 0–900mV to compensate the breakdown voltage variation of individual SiPMs. The TDC jitter together with the digital part is around 37ps. A Coincidence Time Resolution (CTR) of 213.6ps FWHM has been obtained with 3.1×3.1×15m2 LYSO:Ce scintillator crystals and Hamamatsu SiPM matrices (S12643-050CN(X)). Characterization measurements with the chip and its integration into the external plate of the EndoTOFPET-US prototype are presented.

Experimental investigation of silicon photomultipliers as compact light readout systems for gamma-ray spectroscopy applications in fusion plasmas.

A matrix of Silicon Photo Multipliers has been developed for light readout from a large area 1 in. × 1 in. LaBr3 crystal. The system has been characterized in the laboratory and its performance compared to that of a conventional photo multiplier tube. A pulse duration of 100 ns was achieved, which opens up to spectroscopy applications at high counting rates. The energy resolution measured using radioactive sources extrapolates to 3%-4% in the energy range Eγ = 3-5 MeV, enabling gamma-ray spectroscopy measurements at good energy resolution. The results reported here are of relevance in view of the development of compact gamma-ray detectors with spectroscopy capabilities, such as an enhanced gamma-ray camera for high power fusion plasmas, where the use of photomultiplier is impeded by space limitation and sensitivity to magnetic fields.

A large surface photomultiplier based on SiPMs

Light detection through photosensitive devices represents one of the key issues for a large variety of experiments. In the recent years, Silicon PhotoMultipliers (SiPMs) based on limited Geiger-mode avalanche have been extensively studied in view of their future applications. However, their use is strongly limited by their small sensitive surfaces and by the fact that any increment in the surface turns out into an increase of the dark count rate. In the present work we describe the dark count rate reduction obtained by using a FPGA-based logical circuit for fast pre-processing of pulses from a 3×3 matrix of SiPMs. The prototype we developed supports two SiPMs: we show that a rate reduction from 6.6Mcps (Mega counts per second) down to 0.436Mcps at the lowest threshold (0.5 photon-equivalent) and from 1.2kcps down to 0.02cps for the highest threshold (3.5 photon-equivalent) is obtainable.

Development and characterization of a modular acquisition system for a 4D PET block detector

Next generation PET scanners should fulfill very high requirements in terms of spatial, energy and timing resolution. Modern scanner performances are inherently limited by the use of standard photomultiplier tubes . The use of Silicon Photomultiplier (SiPM) matrices is proposed for the construction of a 4D PET module based on LSO continuous crystals, which is envisaged to replace the standard PET block detector. The expected spatial resolution of the module for the photon hit position is below 1 mm, and it will perform at the same time, the Depth Of Interaction (DOI) calculation and the Time Of Flight (TOF) measurement. The use of large area multi-pixel Silicon Photomultiplier (SiPM) detectors requires the development of a multichannel Digital Acquisition system (DAQ) as well as of a dedicated front-end in order not to degrade the intrinsic detector performances. We have developed a flexible and modular DAQ system for the read-out of two modules in time coincidence for Positron Emission Tomography (PET) applications. The DAQ system is based on a previously developed custom front-end ASIC chip (BASIC) which allows to read-out SiPM matrices preserving their spectroscopy and timing capabilities. Here we describe the acquisition system architecture and its characterization measurements.

Silicon Photomultipliers (SiPM) as novel photodetectors for PET

Next generation PET scanners should fulfill very high requirements in terms of spatial, energy and timing resolution. Modern scanner performances are inherently limited by the use of standard photomultiplier tubes. The use of Silicon Photomultipliers (SiPMs) is proposed for the construction of a 4D-PET module of 4.8×4.8 cm 2 aimed to replace the standard PMT based PET block detector. The module will be based on a LYSO continuous crystal read on two faces by Silicon Photomultipliers. A high granularity detection surface made by SiPM matrices of 1.5 mm pitch will be used for the x– y photon hit position determination with submillimetric accuracy, while a low granularity surface constituted by 16 mm 2 SiPM pixels will provide the fast timing information ( t) that will be used to implement the Time of Flight technique (TOF). The spatial information collected by the two detector layers will be combined in order to measure the Depth of Interaction (DOI) of each event ( z). The use of large area multi-pixel Silicon Photomultiplier (SiPM) detectors requires the development of a multichannel Data Acquisition system (DAQ) as well as of a dedicated front-end in order not to degrade the intrinsic detector capabilities and to manage many channels. The paper describes the progress made on the development of the proof of principle module under construction at the University of Pisa.

Characterization of a PET detector head based on continuous LYSO crystals and monolithic, 64-pixel silicon photomultiplier matrices

The characterization of a PET detector head based on continuous LYSO crystals and silicon photomultiplier (SiPM) arrays as photodetectors has been carried out for its use in the development of a small animal PET prototype. The detector heads are composed of a continuous crystal and a SiPM matrix with 64 pixels in a common substrate, fabricated specifically for this project. Three crystals of 12 mm × 12 mm × 5 mm size with different types of painting have been tested: white, black and black on the sides but white on the back of the crystal. The best energy resolution, obtained with the white crystal, is 16% FWHM. The detector response is linear up to 1275 keV. Tests with different position determination algorithms have been carried out with the three crystals. The spatial resolution obtained with the center of gravity algorithm is around 0.9 mm FWHM for the three crystals. As expected, the use of this algorithm results in the displacement of the reconstructed position toward the center of the crystal, more pronounced in the case of the white crystal. A maximum likelihood algorithm has been tested that can reconstruct correctly the interaction position of the photons also in the case of the white crystal.

Advantages and pitfalls of the silicon photomultiplier (SiPM) as photodetector for the next generation of PET scanners

Silicon photomultipliers (SiPM) are a novel type of photodetectors that show great promise for nuclear medicine applications and especially for the next generation of PET scanners. The INFN collaboration DASIPM2 is investigating in depth the properties of the SiPM developed at FBK-irst (Trento, Italy), whose performance compete successfully with those of similar devices produced by commercial companies, but have in addition novel and attractive properties, such as monolithic matrix arrangement. In this paper we illustrate the advantages and pitfalls of the SiPM for PET applications. In particular we report on the most recent experimental results for SiPM and SiPM matrices performances: (i) an intrinsic very good time resolution that coupled to a high PDE could favor time-of-flight PET exploitation; (ii) very high photodetector granularity that allows position determination with continuous crystal and possibly stacking of several layers, i.e., Depth Of Interaction information capability thus paving the way for the construction for the next generation of PET cameras; (iii) MRI compatibility in magnetic field and magnetic field gradient, thus giving the possibility of constructing a state-of-the-art PET insert within an MRI scanner.

Energy, Timing and Position Resolution Studies With 16-Pixel Silicon Photomultiplier Matrices for Small Animal PET

A high resolution small animal PET scanner that employs Silicon Photomultiplier (SiPM) matrices as photodetectors is under development at the University of Pisa and INFN Pisa. The first SiPM matrices fabricated by the Center for Scientific and Technological Research, FBK-irst (Trento, Italy), are being evaluated for this purpose. The devices are composed of 16 (4 times4) pixel elements of 1 mmtimes1 mm in a common substrate. The first tests have been carried out employing the ASIC MAROC2 for the readout. Energy and timing resolution, and position determination tests have been performed coupling both pixellated and continuous LYSO scintillator crystals to the matrix, and the results have been compared with the ones obtained for single SiPMs. The first tests on position determination with continuous crystals and SiPM matrices have been performed. An intrinsic spatial resolution of 0.61 mm FWHM has been obtained.

Energy and Timing Resolution Studies With Silicon Photomultipliers (SiPMs) and 4-Pixel SiPM Matrices for PET

A high performance detector head with matrices of silicon photomultipliers (SiPMs) as photodetectors is under development at the University of Pisa and INFN Pisa. The silicon photomultipliers fabricated at FBK-irst (Trento, Italy) are being evaluated for this purpose. Single SiPM detectors of 1 mm x 1 mm size and the first SiPM test matrices composed of four (2 x 2) pixel elements in a common substrate have been tested with LYSO crystals. The energy and timing resolution of single SiPMs have been evaluated, obtaining an energy resolution of 20% FWHM at 511 keV, and a coincidence timing resolution of 1.4 ns FWHM. In addition, the first tests performed with the SiPM matrices prove the feasibility of such devices.

Novel Silicon Photomultipliers for PET Applications

Silicon photomultipliers (SiPMs) with quantum efficiency maximized for a wavelength between 420 and 470 nm have been developed at ITC-irst Trento (Italy), and are being tested for their application in the construction of a ultra high resolution small animal PET tomograph. The devices have an area of 1 mm times 1 mm and 625 microcells. The breakdown voltage is around 30 V, and the gain of the order of 106. The intrinsic timing resolution is 70 ps rms at the single photoelectron level. The first tests as readout for scintillators show an energy resolution of 21 % FWHM with Na-22 employing LSO crystals. The first matrices of SiPMs have been produced and are being tested.