Silicon photomultiplier based scintillator thermal neutron detector for China Spallation Neutron Source(CSNS)

The energy-resolved neutron imaging spectrometer(ERNI)will be installed in 2022 according to the spectrometer construction plan of the China Spallation Neutron Source(CSNS).The instrument requires neutron detectors with the coverage area of approximately 4 m^(2)in 5°-170°neutron diffraction angle.The neutron detection efficiency needs to be better than 40%at 1 A neutron wavelength.The spatial resolution should be better than 3 mm×50 mm in the horizontal and vertical directions respectively.We develop a one-dimensional scintillator neutron detector which is composed of the^(6)Li F/Zn S(Ag)scintillation screens,the wavelength-shifting fiber(WLSF)array,the silicon photomultipliers(Si PMs),and the self-designed application-specific integrated circuit(ASIC)readout electronics.The pixel size of the detector is designed as 3 mm×50 mm,and the neutron-sensitive area is 50 mm×200 mm.The performance of the detector prototype is measured using neutron beam 20#of the CSNS.The maximum counting rate of 247 k Hz,and the detection efficiency of63%at 1.59 A are obtained.The test results show that the performance of the detector fulfills the physical requirements of the ERNI under construction at the CSNS.

Comparative studies of silicon photomultipliers and traditional vacuum photomultiplier tubes

Silicon photomultipliers （SiPMs） are a new generation of semiconductor-based photon counting devices with the merits of low weight, low power consumption and low voltage operation, promising to meet the needs of space particle physics experiments. In this paper, comparative studies of SiPMs and traditional vacuum photomultiplier tubes （PMTs） have been performed regarding the basic properties of dark currents, dark counts and excess noise factors. The intrinsic optical erosstalk effect of SiPMs was evaluated.

Enhanced collection of scattered photons in nonlinear fluorescence microscopy by extended epi-detection with a silicon photomultiplier array

To maximize signal collection in nonlinear optical microscopy,non-descanned epi-detection is generally adopted for in vivo imaging.However,because of severe scattering in biological samples,most of the emitted fluorescence photons go beyond the collection angles of objectives and thus cannot be detected.Here,we propose an extended detection scheme to enhance the collection of scattered photons in nonlinear fluorescence microscopy using a silicon photomultiplier array ahead of the front apertures of objectives.We perform numerical simulations to demonstrate the enhanced fluorescence collection via extended epi-detection in the multi-photon fluorescence imaging of human skin and mouse brain through craniotomy windows and intact skulls.For example,with red fluorescence emission at a depth of 600μm in human skin,the increased collection can be as much as about 150%with a 10×,0.6-NA objective.We show that extended epi-detection is a generally applicable,feasible technique for use in nonlinear fluorescence microscopy to enhance signal detection.

Design and development of compact readout electronics with silicon photomultiplier array for a compact imaging detector

This work aims at developing compact readout electronics for a compact imaging detector module with silicon photomultiplier （SPM） array. The detector module consists of a LYSO crystal array coupling with a SensL’s 4×4 SPM array. A compact multiplexed readout based on a discretized positioning circuit （DPC） was developed to reduce the readout channels from 16 to 4 outputs. Different LYSO crystal arrays of 4×4, 8×8 and 12×12 with pixel sizes of 3.2, 1.6 and 1.0 mm respectively, have been tested with the compact readout board using a 137 Cs source. The initial results show that the compact imaging detector module with the compact multiplexed readout could clearly resolve 1 mm×1 mm×10 mm LYSO scintillation crystal array except those at the edges. The detector’s intrinsic spatial resolution up to 1 mm can be achieved with the 3 mm×3 mm size SPMArray4 through light sharing and compact multiplexed readout. Our results indicate that this detector module is feasible for the development of high-resolution compact PET.

Low-power SiPM readout BETA ASIC for space applications

The BETA application-specific integrated circuit(ASIC)is a fully programmable chip designed to amplify,shape and digitize the signal of up to 64 Silicon photomultiplier(SiPM)channels,with a power consumption of approximately~1 mW/channel.Owing to its dual-path gain,the BETA chip is capable of resolving single photoelectrons(phes)with a signal-to-noise ratio(SNR)>5 while simultaneously achieving a dynamic range of~4000 phes.Thus,BETA can provide a cost-effective solution for the readout of SiPMs in space missions and other applications with a maximum rate below 10 kHz.In this study,we describe the key characteristics of the BETA ASIC and present an evaluation of the performance of its 16-channel version,which is implemented using 130 nm technology.The ASIC also contains two discriminators that can provide trigger signals with a time jitter down to 400 ps FWHM for 10 phes.The linearity error of the charge gain measurement was less than 2%for a dynamic range as large as 15 bits.

Development of a scintillating-fiber-based beam monitor for the coherent muon-to-electron transition experiment

The coherent muon-to-electron transition(COMET)experiment is a leading experiment for the coherent conversion of μ^(-)N→e^(-)N using a high-intensity pulsed muon beamline,produced using innovative slow-extraction techniques.Therefore,it is critical to measure the muon beam characteristics.We set up a muon beam monitor(MBM),where scintillating fibers woven in a cross shape were coupled to silicon photomultipliers to measure the spatial profile and timing structure of the extracted muon beam for the COMET.The MBM detector was tested successfully with a proton beamline at the China Spallation Neutron Source and took data with good performance in the commissioning run.The development of the MBM,including its mechanical structure,electronic readout,and beam measurement results,are discussed.

Design and development of multi-channel front end electronics based on dual-polarity charge-to-digital converter for SiPM detector applications

With the development of silicon photomultiplier(SiPM)technology,front-end electronics for SiPM signal processing have been highly sought after in various fields.A compact 64-channel front-end electronics(FEE)system achieved by fieldprogrammable gate array-based charge-to-digital converter(FPGA-QDC)technology was built and developed.The FEE consists of an analog board and FPGA board.The analog board incorporates commercial amplifiers,resistors,and capacitors.The FPGA board is composed of a low-cost FPGA.The electronics performance of the FEE was evaluated in terms of noise,linearity,and uniformity.A positron emission tomography(PET)detector with three different readout configurations was designed to validate the readout capability of the FEE for SiPM-based detectors.The PET detector was made of a 15×15 lutetium–yttrium oxyorthosilicate(LYSO)crystal array directly coupled with a SiPM array detector.The experimental results show that FEE can process dual-polarity charge signals from the SiPM detectors.In addition,it shows a good energy resolution for 511-keV gamma photons under the dual-end readout for the LYSO crystal array irradiated by a Na-22 source.Overall,the FEE based on FPGA-QDC shows promise for application in SiPM-based radiation detectors.

Design and performance of a high-speed and low-noise preamplifier for SiPM

Considering the R&D for upgrading the K^(0)_(L) andμdetectors in the Belle II experiment using a scintillator and silicon pho-tomultiplier(SiPM),we designed a compact high-speed and low-noise preamplifier.The preamplifier demonstrated a good gain stability,bandwidth of 426 MHz,baseline noise level ofσ≈0.6 mV,dynamic range of up to170 mV of the input signal amplitude,good time resolution of 20 ps,and it can be comprehensively applied to SiPMs.Adopting pole-zero-cancelation in the preamplifier reduces both the rise and fall times of the SiPM signal,which can significantly improve the time resolution and reduce the pile-up when using a large SiPM or an array of SiPMs.Various combinations of the preamplifier and several types of SiPMs demonstrated time resolutions better than 50 ps for most cases;when the number of detected photons was larger than 60,a time resolution of approximately 25 ps was achieved.

Performance optimization of scintillator neutron detectors for EMD in CSNS

Chinese Spallation Neutron Source(CSNS) has successfully produced its first neutron beam in 28th August 2017. It has been running steadily from March, 2018. According to the construction plan, the engineering materials diffractometer(EMD) will be installed between 2019–2023. This instrument requires the neutron detectors with the cover area near3 m2in two 90° neutron diffraction angle positions, the neutron detecting efficiency is better than 40%@1A, and the spatial resolution is better than 4 mm×200 mm in horizontal and vertical directions respectively. We have developed a onedimensional position-sensitive neutron detector based on the oblique6Li F/Zn S(Ag) scintillators, wavelength shifting fibers,and Si PMs(silicon photomultipliers) readout. The inhomogeneity of the neutron detection efficiency between each pixel and each detector module, which caused by the inconsistency of the wave-length shifting fibers in collecting scintillation photons, needs to be mitigated before the installation. A performance optimization experiment of the detector modules was carried out on the BL20(beam line 20) of CSNS. Using water sample, the neutron beam with Φ5 mm exit hole was dispersed related evenly into the forward space. According to the neutron counts of each pixel of the detector module, the readout electronics threshold of each pixel is adjusted. Compared with the unadjusted detector module, the inhomogeneity of the detection efficiency for the adjusted one has been improved from 69% to 90%. The test result of the diffraction peak of the standard sample Si showed that the adjusted detector module works well.

Preliminary results for the design,fabrication,and performance of a backside-illuminated avalanche drift detector

The detection of low-level light is a key technology in various experimental scientific studies. As a photon detector, the silicon photomultiplier （SiPM） has gradually become an alternative to the photomultiplier tube （PMT） in many applications in high-energy physics, astroparticle physics, and medical imaging because of its high photon detection efficiency （PDE）, good resolution for single-photon detection, insensitivity to magnetic field, low operating voltage, compactness, and low cost. However, primarily because of the geometric fill factor, the PDE of most SiPMs is not very high; in particular, for those SiPMs with a high density of micro cells, the effective area is small, and the bandwidth of the light response is narrow. As a building block of the SiPM, the concept of the backside-illuminated avalanche drift detector （ADD） was first proposed by the Max Planck Institute of Germany eight years ago; the ADD is promising to have high PDE over the full energy range of optical photons, even ultraviolet light and X-ray light, and because the avalanche multiplication region is very small, the ADD is beneficial for the fabrication of large-area SiPMs. However, because of difficulties in design and fabrication, no significant progress had been made, and the concept had not yet been verified. In this paper, preliminary results in the design, fabrication, and performance of a backside-illuminated ADD are reported; the difficulties in and limitations to the backside-illuminated ADD are analyzed.

A simulation study for a cost-effective PET-like detector system intended to track particles in granular assemblies

Since many industrial applications rely on the processing of densely packed and moving granular ma-terial,obtaining bulk internal information on the particle movement inside the reactors is of great importance.Such information can be delivered by Positron Emission Particle Tracking(PEPT).By marking pellets with a positron-emitting radioisotope,the position of these tracer particles can be determined via the time-of-flight differences of the emitted gamma-ray pairs.The current paper proposes a PET-like detector system based on cost-effective organic plastic scintillators instead of the more common but expensive inorganic scintillators.This system is currently under construction and was tested for its resolution and efficiency in this simulation study.Using Monte Carlo simulations and the software toolkit Geant4,three different geometries(an empty glass box,a generic grate system,and a cubic box of 1 m3 completely filled with pellets)were investigated,leading to a spatial resolution in the millimeter range and an efficiency,defined as the ratio of reconstructed decay locations to simulated decays,of 2.7%,1.4%,and 0.3%.

Current status and development of CMOS SiPM for scintillator-based radiation detectors toward all-digital sensors[Invited]

Modern scintillator-based radiation detectors require silicon photomultipliers(Si PMs)with photon detection efficiency higher than 40%at 420 nm,possibly extended to the vacuum ultraviolet(VUV)region,single-photon time resolution(SPTR)<100 ps,and dark count rate(DCR)<150 kcps/mm^(2).To enable single-photon time stamping,digital electronics and sensitive microcells need to be integrated in the same CMOS substrate,with a readout frame rate higher than 5 MHz for arrays extending over a total area up to 4 mm×4 mm.This is challenging due to the increasing doping concentrations at low CMOS scales,deep-level carrier generation in shallow trench isolation fabrication,and power consumption,among others.The advances at 350 and 110 nm CMOS nodes are benchmarked against available Si PMs obtained in CMOS and commercial customized technologies.The concept of digital multithreshold Si PMs with a single microcell readout is finally reported,proposing a possible direction toward fully digital scintillator-based radiation detectors.

A simulation study on spatial and time resolution for a cost-effective positron emission particle tracking system

This work is the second part of a simulation study investigating the processing of densely packed and moving granular assemblies by positron emission particle tracking (PEPT).Since medical positron emission tomography (PET) scanners commonly used for PEPT are very expensive,a PET-like detector system based on cost-effective organic plastic scintillator bars is being developed and tested for its capabilities.In this context,the spatial resolution of a resting positron source,a source moving on a freely designed model path,and a particle motion given by a discrete element method (DEM) simulation is studied using Monte Carlo simulations and the software toolkit Geant4.This not only extended the simulation and reconstruction to a moving source but also significantly improved the spatial resolution compared to previous work by adding oversampling and iteration to the reconstruction algorithm.Furthermore,in the case of a source following a trajectory developed from DEM simulations,a very good resolution of about 1 mm in all three directions and an average 3D deviation between simulated and reconstructed events of 2.3 mm could be determined.Thus,the resolution for realistic particle motion within the generic grate system (which is the test rig for further experimental studies) is well below the smallest particle size.The simulation of the dependence of the reconstruction accuracy on tracer particle location revealed a nearly constant efficiency within the entire detector system,which demonstrates that boundary effects can be neglected.

The technology for detection of gamma-ray burst with GECAM satellite

Introduction The main physical objective of the GECAM satellite is to detect gamma-ray bursts,which is related to gravitational waves of double compact object mergers.The GECAM satellite also detects and investigates various bursts of high-energy celestial bodies.Purposes and methods In this study,we designed,developed and calibrated the payload and launched it into orbit with GECAM satellite.The payload consists of the gamma ray detector(GRD,for detecting 4 keV–4 MeV X/γray),the charged particle detector(CPD,for detecting 150 keV–5 MeV charged particle),and the electronic box(EBOX).The all-sky field coverage is achieved via two 229-degree large-area satellites positioned 180 degrees apart and are on opposite sides of the geo-center.Each satellite is equipped with 25 GRDs and 8 CPDs;thus,the satellite can identify charged particle bursts in space.Gamma-ray detectors adopt lanthanum bromide crystal technology combined with silicon photomultipliers.This is the first time that this technology was used massively in space detectors.Conclusions The GECAM satellite can quickly determine the direction of gamma-ray bursts(positioning)via indexing and fitting method,while the transmit variability,energy spectrum and direction of the gamma-ray bursts guide subsequent observations through the Beidou-3 RDSS in quasi-real time.It will play an important role in the study of high energy celestial bursts.

The data acquisition algorithm designed for the SiPM-based detectors of GECAM satellite

Background The Gravitational Wave High-energy Electromagnetic Counterpart All-sky Monitor(GECAM)consists of 2 microsatellites,each of which contains 25 GRD(LaBr3)detectors and 8 CPD(plastic scintillator)detectors.Method silicon photomultiplier(SiPM)array is used to read each detector.The output signal of these detectors with SiPM array is very special and challenging to readout.In this study,a novel data acquisition(DAQ)algorithm for these detectors is designed and implemented,and the content of the output event packet is defined.Result and Conclusion The performances,including the event acquisition efficiency of this DAQ algorithm,are extensively verified through experimental tests.From the on-ground and in-flight tests,this algorithm has excellent performance despite the very limited resources and short development time of GECAM mission.

Performance of MPPC at low temperature

The performance of a MultiPixel Photon Counter （MPPC） from room to liquid nitrogen tem- peratures were studied. The gain, the noise rate and bias voltage of the MPPC as a function of temperature were obtained. The experimental results show that the MPPC can work at low temperatures. At nearly liquid nitrogen temperatures, the gain of the MPPC drops obviously to 35% and the bias voltage drops about 9 V compared with that at room temperature. The thermal noise rate from 106 Hz/mm at room temperature drops abruptly to 0 Hz/mm at -100℃. The optimized operation point can be acquired by the experiment.

Prototype of an array SiPM-based scintillator Compton camera for radioactive materials detection

Purpose The Compton camera,which visualizes the distribution of gamma-ray sources based on the kinematics of Compton scattering,has advantage of wide field of view,broad range of energy and compact structure.Methods In this study,we proposed a prototype of Compton camera,which included array silicon photomultiplier(SiPM)-based position-sensitive detectors,data acquisition(DAQ)system and image reconstruction system.The detectors were composed of Ce-doped Gd_(3)Al_(2)Ga_(3)O_(12) scintillator arrays and pixel Si-PM arrays.In DAQ system,symmetric charge division circuit,impedance bridge circuit and the delay coincidence algorithm were designed to record coincidence events.Simple back-projection algorithm and list-mode maximum likelihood expectation maximization algorithm were adopted for image reconstruction.The coordinate of longitude and latitude was used for image fusion.Results The performance of this Compton camera prototype system was evaluated.The results indicated that this system was able to locate a ^(137)Cs point source within 20 s with the corresponding radiation dose of~1.0μSv/h.The angular resolution of point source was~7°(FWHM),and the total energy resolution of 662 keV was 7.2%.Furthermore,we succeeded in separating two point sources of different energy[^(22)Na(511 keV),^(137)Cs(662 keV)]in laboratory test.Conclusions This prototype of scintillator Compton camera offers capabilities for applications like source term investigation and radioactive materials detection.

Evaluation of a position-sensitive prototype detector unit for fast neutron imaging and spectroscopy

Purpose A novel fast neutron scatter camera with capabilities of neutron imaging and spectroscopy is under development.The detection principle is based on multiple neutron–proton(n–p)elastic scattering interactions in organic scintillator.In order to improve position measurement accuracy of recoil protons,a position-sensitive prototype detector unit has been designed and characterized experimentally.Methods The presented detector unit consisted of a plastic scintillator sheet of 10 cm×10 cm×1 cm dimensions and two groups(6×2)of wavelength-shifting fibers with orthogonal directions embedded into grooves on two opposite scintillator surfaces.Scintillation signals were read out by silicon photomultipliers(SiPMs).A collimated Sr-90 radioactive source was utilized for system calibration and position resolution measurement.Results Light output of the unidimensional six fiber channels from one side of the detector unit was calibrated to be 14.45 photoelectrons per MeVee.Position resolution of the detector unit was measured to be 0.35–0.44 times fiber pitch,corresponding to 5.48 mm for proton recoil energy interval of 1.63–2.60 MeV,and 4.60 mm for proton recoil energy interval of 4.82–5.50 MeV.Energy threshold for recoil proton localization was estimated to be 1.18 MeV.Conclusion The results shown satisfy basic requirements of the scatter camera,while space exists for further improvements.The positioning performance optimization consists of three aspects.The first one is to increase the fiber diameter so as to reduce signal loss.The second one is to depress dark rate of the SiPMs.The last one is to decrease the number of channels involved in position reconstruction by narrowing the scintillation signal distribution function of the detector unit.

Quality assurance test and failure analysis of SiPM arrays of GECAM satellites

Background The Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor(GECAM)satellite developed a SiPM-based gamma-ray detector to monitor the gravitational wave-related GRBs and guide subsequent observations in other wavelengths of EM.Purpose As all the available SiPM devices belong to commercial grade,quality assurance tests need to be performed in accordance with the aerospace specifcations.Methods In the SiPM application of GECAM,quality assurance experiments were conducted.The mechanism of the failure of SiPM devices was analyzed during the development process.Result Based on the quality assurance test results,the fnal pass rate of SiPM array was 95%.Based on the failure analysis,it was found that a piece of SiPM had a leakage channel after longtime operation due to device defects.Conclusion According to the accumulated experience,in the reliability test of SiPM,it is necessary to pay special attention to test the impedance of each pin of SiPM to ground and confrm that the power switch state of SiPM is controllable.

Development and evaluation of a double-plane detector system for multi-radionuclide imaging

Purpose To develop a multi-radionuclide imaging system with a flexible and compact structure that has a potential for breast and other applications,and to evaluate its performances under both positron emission tomography and single photon emission imaging conditions.Methods The plane detector was composed of 5×6 blocks with an effective detection area of 168.6 mm×202.4 mm.Each block consisted of a 16×16 LYSO array.The pixel size is 1.9 mm×1.9 mm×15 mm.An 8×8 silicon photomultiplier(SiPM)array with SensL’s C-30035 sensors was coupled to the LYSO array,separated by a 1.5-mm-thick glass.To minimize the influence of temperature on the detector,the active part of the front-end electronics was kept away from SiPMs.Self-designed data acquisition system and reconstruction software were utilized to evaluate the performances of the whole system.Results All the blocks had excellent pixels identification.An average energy resolution of 11.39%for 511 keV and 21.37%for 140 keV was obtained.In the PET mode,the best spatial resolution was better than 2 mm and the system sensitivity reached up to 11.05%at 60 mm distance.In the single photon emission imaging mode,a spatial resolution better than 3 mm was obtained.Conclusion The results indicated that the system has a good overall performance and can be used in breast imaging and other general PET applications.It also has the potential to be used for single photon emission imaging.In pursuit of a better spatial resolution of cross-plane,PSF and DOI technology will be developed in the next work.For specific applications,further improvement of the detector system such as performance evaluation with phantoms will be carried out.