Fast Photomultiplier Research Articles

New readout system of the FATIMA detectors based on Silicon Photomultipliers arrays

We present a new readout system based on large area Silicon Photomultipliers arrays coupled with cylindrical 1.5” × 2” LaBr3(Ce) FATIMA-type crystals. This readout achieves the fast-timing capabilities of such crystals coupled to the usual Photomultiplier Tubes. Energy calibration was measured with 137Cs and 152Eu standard radioactive sources, while the timing performances were investigated with a 60Co radioactive source. We benchmark our results against the corresponding results obtained with the fast R9779 Photomultiplier tubes and highlight the importance of achieving similar energy and timing performances for nuclear structure experiments. The FWHM energy resolution for the 1.5” × 2” LaBr3(Ce) crystal coupled with the SiPM and PMT was found to be 3.31(2)% and 3.85(1)%, respectively, for the 661.6 keV transition of the 137Cs source. The timing resolution was measured between a conical crystal known for its fast response and a cylindrical crystal coupled to a SiPM or PMT readout. We obtain values of FWHM = 230(1) ps and 232(1) ps, respectively, between the 1173.2–1332.5 keV transitions of the 60Co source. In addition, a temperature effect compensation circuit was developed to maintain a good stability of the gain during long measurements, typical for in-beam/off-beam experiments in nuclear physics.

3D-Heterojunction based on Embedded Perovskite Micro-sized Single Crystals for Fast Photomultiplier Photodetectors with Broad/narrowband Dual-mode.

A fast photomultiplier photodetector with a broad/narrowband dual mode was implemented using a new 3D heterostructure based on embedded perovskite micro-sized single crystals. Because the single-crystal size is smaller than the electrode size, the active layer can be divided into the perovskite microcrystalline part for charge transport and the polymer-embedded part for charge storage. This induces an additional radical interface in the 3D heterojunction structure, and allows the photogenerated built-in electric field in radical direction, especially when the energy levels between the perovskite and embedding polymer are similar. This type of heterojunction has a small radial capacitance that can effectively reduce carrier quenching and accelerate the carrier response. By controlling the applied bias direction, up to 300-1000% external quantum efficiency (EQE) and microsecond response can be achieved not only in the wide range of ultraviolet to visible light from 320nm to 550nm, but also in the narrow-band response with a full width at half minimum (FWHM) of 20nm. This shows great potential for applications in integrated multifunctional photodetectors. This article is protected by copyright. All rights reserved.

Investigation of the Operation of a Fast Photomultiplier in a Scintillation Alpha-Particle Detector

Investigation of the Operation of a Fast Photomultiplier in a Scintillation Alpha-Particle Detector

Picosecond Timing Electronics for a DIRC-Like Detector at the Super Tau-Charm Facility

The DIRC-like time-of-flight detector (DTOF) at the Super Tau-Charm Facility (STCF) in China is a Cherenkov light detector that uses the TOF technique to identify charged particles. To achieve the expected target that provides a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3\sigma \pi $ </tex-math></inline-formula> /K separation at 2-Ge/c momentum, a single-photon time resolution of better than 50 ps is required, while the contribution from electronics should be lower than 15 ps. To meet the requirements with high channel count integration, the timing electronics using leading-edge discrimination and field-programmable gate array (FPGA)-based time-to-digital converters (TDCs) are employed in the DTOF detector. This article reports the results of the first phase of project where the timing electronics with 128 channels has been constructed and its performance has been evaluated. Including the uncertainty of system clock distribution and synchronization, the intrinsic timing resolution of the electronics is better than 10-ps rms. Taking fast microchannel plate photomultiplier tubes (MCP-PMTs) as Cherenkov photodetectors and adopting time-over-threshold (TOT) measurement for time walk correction, the measured single-photon time resolutions are better than 40-ps rms. The test results confirm that the proposed timing electronics has advantages of high precision and high integration, which is highly demanded in future picosecond timing detectors.

Cherenkov probes and runaway electrons diagnostics

The beams of fast runaway electrons (RE), which are often produced during tokamak discharges, are particularly dangerous and can induce serious damages of the vacuum vessel and internal components of the machine. The proper and fast diagnostics of RE beams is essential for controlling the discharge, e.g., by early mitigation of disruptions and potentially dangerous RE beams. The diagnostics of RE beams is usually based on measurements of the radiation emitted either by these electrons, or as a result of their interactions with plasma and/or vessel walls. Such a radiation is usually recorded by the means of probes placed outside the vacuum vessel. The method developed by our team is based on the probe located inside the vacuum vessel. The probe can be used to detect highly localized RE bunches and to determine their spatial and temporal characteristics. During last few years, the NCBJ team have developed and used the RE diagnostics based on the Cherenkov effect observed in diamond radiators coupled with fast photomultipliers. During the investigated discharges, the probe was inserted into the vacuum vessel, and its head was placed at the plasma edge, where fast RE are expected. A correlation between signals recorded using our probes and other diagnostics, e.g., hard x-ray signals, was also studied. In this paper, we present recent results of the RE measurements by means of Cherenkov probes, which were performed in the COMPASS and TCV tokamaks.

Scintillating properties of today available lead tungstate crystals

In the context of the ClearMind project, we measured the scintillating properties, as induced from gamma ray interactions, of today available PbWO4 crystal. We measured scintillation's yields and time constants by measuring the signal shape measured on a fast photo-multiplier and deconvoluting it from the instrumental effects. For the doped crystals at room temperature, we measured a fast scintillation component, with time constants of 2 ns, 55 % of the total light yield, and a slow component of 6 ns. We observe a significant increase of the light yield for the slow component when the temperature decreases and simultaneous increase of the time constants, but no increase in the fast component light yield. Our measurements reproduce the main qualitative features of PbWO4 crystals quoted in the literature. Quantitatively though, we measured significantly shorter time constants and larger light yields. This is explained by a rigorous treatment of the instrumental contributions in the measurements. Results are discussed and prospect for future developments “tailored” for the ClearMind project are presented.

Preliminary Study on the Timing Characteristics of a Fast SiPM for the TOF of the Beam Line in IHEP

The upgrade of the BESIII end cap time-of-flight (TOF) detector needs to achieve a ~40-ps time resolution level to provide high-performance reference time for beam testing. Fast silicon photomultiplier tubes (SiPMs) have excellent time characteristics and the transition time spread (TTS) can reach tens of picoseconds. Therefore, SiPMs are selected to replace the PMTs in T0 detectors. In this article, we describe that the time characteristics of a fast SiPM and T0 system were studied using a high-speed real-time oscilloscope. In order to obtain the optimal time resolution, coupling techniques of the plastic scintillators and SiPMs were studied. Single-ended coupling between a SiPM and a plastic scintillator can obtain the best time resolution.

The Coherent Particle-Oscillation Excitation System at the VEPP-4M Collider

A system for excitation of coherent oscillations of a bunch of particles was created to study the beam dynamics at the VEPP-4M electron-positron collider; it consisted of a pulse generator, a beam deflection device (kicker), and a control and synchronization system. The system has two independent channels for the excitation of horizontal and vertical oscillations and makes it possible to excite oscillations of a given bunch of particles. For observations of beam oscillations, a system for measuring the position of the beam in the reverse mode is used, as well as a fast multichannel photomultiplier tube (profilometer). The design and results of operation of high-voltage nanosecond shock generators with a current pulse duration of 200–250 ns at the base, a voltage up to 25 kV and a current up to 2 kA are described. Using constructive solutions, the durations of the fronts of the output pulses were reduced, which made it possible to avoid the excitation of neighboring bunches. Testing the generators for their working loads gave the following results: a horizontal impact pulse of 30 ns and a vertical impact of 50 ns, a horizontal impact pulse tip duration of ~20 ns, a maximum pulse amplitude of 25 kV, and a time instability (jitter) of ±1 ns. The results of measurements of the beam parameters obtained using this system are presented.

Absolute SiO concentration imaging in low-pressure nanoparticle-synthesis flames via laser-induced fluorescence

In this paper, we present a strategy for imaging measurements of absolute concentration values of gas-phase SiO in the combustion synthesis of silica, generated from the reaction of hexamethyldisiloxane (HMDSO) precursor in a lean (ϕ = 0.6) hydrogen/oxygen/argon flame. The method is based on laser-induced fluorescence (LIF) exciting the Q(42) rotational transition within the A1Π − X1Σ (1, 0) electronic band system of SiO at 231 nm. Corrections for temperature-dependent population of the related ground state are based on multi-line SiO–LIF thermometry utilizing transitions within the A1Π − X1Σ (0, 0) electronic band around 234 nm. Corrections for local collisional quenching are based on measured effective fluorescence lifetimes from the temporal signal decay using a short camera gate stepped with respect to the laser pulse. This fluorescence lifetime measurement was confirmed with additional measurements using a fast photomultiplier. The resulting semi-quantitative LIF signal was photometrically calibrated using Rayleigh scattering from known gas samples at various pressures and laser energies as well as with nitric oxide LIF. The obtained absolute SiO concentration values in the HMDSO-doped flames will serve as a stringent test case for recently developed flame kinetic mechanisms for this class of gas-borne silicon dioxide nanoparticle synthesis.

Status of the large size telescopes and medium size telescopes for the Cherenkov Telescope Array observatory

Abstract The Cherenkov Telescope Array (CTA) is the next generation of ground-based observatory in the Very High Energy (VHE) gamma-ray domain. The observatory, operating in an open, all-sky mode, will consist of two sites, one in the Northern Hemisphere, at Observatorio Roque de los Muchachos (La Palma, Spain), and another in the Southern Hemisphere. CTA will implement Imaging Atmospheric Cherenkov Telescopes (IACTs) of large, medium and small size, mapping the VHE sky with an unprecedented sensitivity in an extended energy range. In its baseline design, 4 Large Size Telescopes (LSTs) will operate in coincidence in each site, dominating the CTA sensitivity in the 20 GeV – 150 GeV gamma-ray band, while the CTA core energy range, from 150 GeV to 5000 GeV, will be best covered by Medium Size Telescopes (MSTs), 25 in CTA-South and 15 in CTA-North. Each LST will be based on a 23 m diameter segmented, light-weight reflector , incorporating an active mirror control system, and a fast Photo-Multiplier Tube (PMT) camera. These features will allow CTA to observe extragalactic sources up to redshifts larger than two and to improve the sensitivity in observing gamma-ray transients. A prototype LST is currently under construction at the CTA-North site. A commissioning and validation phase will follow, which will mark the beginning for the construction of the rest of the LSTs of CTA-North and CTA-South. The MSTs, with an aperture of 10–12 m, are being explored in two different design options. One is based on the traditional IACT Davies–Cotton optical system and PMT-based cameras (FlashCam and NectarCAM), which is perfected after the experience from current HESS, MAGIC and VERITAS observatories. An alternative approach, based on the novel Schwarzschild–Couder optical system and Silicon-Photo-Multiplier-based camera, is also being developed to improve angular resolution. In this contribution, we will review the status of the prototypes of the LST and both MSTs for CTA.

Вимірювання періоду напіврозпаду ядра 212Po за допомогою насиченого торієм рідкого сцинтилятора

Precise measurement of half-life of $^{212}$Po (one of the daughter nuclides in radioactive chain of $^{232}$Th) was realized by means of liquid scintillator based on toluene doped by complex of thorium and trioctylphosphine oxide with concentration of Th $\sim0.1$ mass %. Fast photomultiplier tube and high frequency oscilloscope were used to acquire the scintillation signals waveforms. The algorithms were developed to find pairs of $^{212}$Bi beta-decays and subsequent $^{212}$Po alpha-decays, to calculate time differences between the events in the pair, and to build $^{212}$Bi beta-decay and $^{212}$Po alpha-decay energy spectra. Preliminary the $^{212}$Po half-life is $T_{1/2} = (294.8 \pm 1.9)$ ns. The experiment is in progress aiming at reduction of the statistical and systematic uncertainties.

Approximations of coincidence time resolution models of scintillator detectors with leading edge discriminator

Coincidence time resolution (CTR) of scintillator detectors is of high importance in high energy physics, medical imaging, and many other time-of-flight (TOF) application areas. Recent progress in developments of fast silicon photomultipliers (SiPM) and dedicated fast timing electronics resulted in significant improvements in CTR of SiPM-based scintillator detectors. CTR of 10 ps is considered as an ultimate goal of these improvements. Approaching to that goal, the most sophisticated devices (multichannel digital SiPM, 3D SiPM) and methods (TOF estimators based on multi-photon time-stamps, intense computational algorithms) are evaluated.Despite these cutting-edge approaches, conventional analog SiPMs and vacuum PMTs with a conventional leading-edge discriminator (LED) are expected to be relevant solutions in large-scale experiments and applications for a long time. However, CTR estimation even in these cases requires specific numerical or Monte Carlo simulations because to the best of the author’s knowledge, there are no widely recognized closed-form expressions of CTR.This study is an attempt to develop simple and reasonably realistic closed-form approximations of the CTR from a filtered marked point process model of the photomultiplier response, and clarify the CTR dependence on the main scintillator detection parameters.

Probing Cherenkov and Scintillation Light Separation for Next-Generation Neutrino Detectors

The ability to separate Cherenkov and scintillation signals in liquid scintillator detectors would enable outstanding background rejection for next-generation neutrino experiments. Reconstruction of directional information, ring imaging, and sub-Cherenkov threshold detection all have the potential to substantially improve particle and event identification. The Cherenkov-Scintillation Separation (CHESS) experiment uses an array of small, fast photomultipliers (PMTs) and state-of-the-art electronics to demonstrate the reconstruction of a Cherenkov ring in a scintillation medium based on photon hit times and detected charge. This setup has been used to characterize the ability to detect Cherenkov light in a range of target media. We show results with pure organic scintillator (LAB) and the prospects with scintillators with a secondary fluor (LAB/PPO). There are future plans to deploy the newly developed water-based liquid scintillator, a medium with a higher Cherenkov/Scintillation light yield ratio than conventional pure liquid scintillators, enhancing the visibility of the less abundant Cherenkov light in the presence of scintillation light. These results can inform the development of future large-scale detectors, such as the proposed Theia experiment, or other large detectors at underground laboratories such as the far-site of the new Long Baseline Neutrino Facility at the Sanford Underground Research Facility. CHESS detector calibrations and commissioning will be discussed, and the latest results will be presented.

Two-wavelength LIDAR Thomson scattering for ITER core plasma

Our proposal for a LIDAR Thomson scattering system to measure Te and ne profiles in the ITER core plasma, is based on experience with the LIDAR system on JET, which is still operational after 30 years. The design uses currently available technology and complies with the measurement requirements given by ITER. In addition, it offers the following advantages over the conventional imaging approach currently being adopted by ITER: 1) No gas fill of the vessel required for absolute calibration. 2) Easier alignment. 3) Measurements over almost the complete plasma diameter. 4) Two mirrors only as front optics. For a given laser wavelength the dynamic range of the Te measurements is mainly limited by the collection optics' transmission roll-off in the blue and the range of spectral sensitivity of the required fast photomultipliers. With the originally proposed Ti:Sapphire laser, measurements of the envisaged maximum temperature of 40 keV are marginally possible. Here we present encouraging simulation results on the use of other laser systems and on the use of two lasers with different wavelength. Alternating two wavelengths was proposed already in 1997 as a method for calibrating the transmission of the collection system. In the present analysis, the two laser pulses are injected simultaneously. We find that the use of Nd:YAG lasers operated at fundamental and second harmonic, respectively, yields excellent results and preserves the spectral recalibration feature.

Probe-hosted silicon photomultipliers for time-domain functional near-infrared spectroscopy: phantom and in vivo tests.

We report the development of a compact probe for time-domain (TD) functional near-infrared spectroscopy (fNIRS) based on a fast silicon photomultiplier (SiPM) that can be put directly in contact with the sample without the need of optical fibers for light collection. We directly integrated an avalanche signal amplification stage close to the SiPM, thus reducing the size of the detection channel and optimizing the signal immunity to electromagnetic interferences. The whole detection electronics was placed in a plastic screw holder compatible with the electroencephalography standard cap for measurement on brain or with custom probe holders. The SiPM is inserted into a transparent and insulating resin to avoid the direct contact of the scalp with the 100-V bias voltage. The probe was integrated in an instrument for TD fNIRS spectroscopy. The system was characterized on tissue phantoms in terms of temporal resolution, responsivity, linearity, and capability to detect deep absorption changes. Preliminary in vivo tests on adult volunteers were performed to monitor hemodynamic changes in the arm during a cuff occlusion and in the brain cortex during a motor task.

Tracking the evolution of soot particles and precursors in turbulent flames using laser-induced emission

A point-wise, time-resolved optical technique is employed to track simultaneously the evolution of soot particles and soot precursors in a turbulent flame of ethylene/nitrogen (1/1 by vol.). A picosecond laser, 80ps@266nm is used to measure scattering and laser-induced fluorescence (LIF) in selected UV and visible bands while Laser-induced incandescence (LII) is excited using a pulsed laser with 8ns@1064nm. Fast photomultiplier tubes are used to ensure time-resolved measurements and LIF decay times of the order of 3.5ns are detected. The LIF signals are attributed to nanoparticles or condensed phase species made up of PAHs, whereas LII was correlated with soot. Data conditioning based on the noise level was made to delineate the potentially large influence of intermittency on the statistics of the detected signals. It was found that LIF signals with long decay times were detected well before the onset of soot particles, as seen by LII, and these continue well into the maximum soot formation region. The correlation between the LII and LIF signals confirmed the co-presence of small nanoparticles together with high concentrations of mature soot. Analysis of conditioned mean soot concentration suggests that the intermittency occurring at the edge and tip of the flame does not locally decrease the soot concentration since large LII signals were still detected. These simultaneous, time-resolved measurements are extremely useful to provide insights on the evolution of combustion-generated particles in turbulent sooting flames.

Multichannel emission spectrometer for high dynamic range optical pyrometry of shock-driven materials

An emission spectrometer (450-850 nm) using a high-throughput, high numerical aperture (N.A. = 0.3) prism spectrograph with stepped fiberoptic coupling, 32 fast photomultipliers and thirty-two 1.25 GHz digitizers is described. The spectrometer can capture single-shot events with a high dynamic range in amplitude and time (nanoseconds to milliseconds or longer). Methods to calibrate the spectrometer and verify its performance and accuracy are described. When a reference thermal source is used for calibration, the spectrometer can function as a fast optical pyrometer. Applications of the spectrometer are illustrated by using it to capture single-shot emission transients from energetic materials or reactive materials initiated by km⋅s-1 impacts with laser-driven flyer plates. A log (time) data analysis method is used to visualize multiple kinetic processes resulting from impact initiation of HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) or a Zr/CuO nanolaminate thermite. Using a gray body algorithm to interpret the spectral radiance from shocked HMX, a time history of temperature and emissivity was obtained, which could be used to investigate HMX hot spot dynamics. Finally, two examples are presented showing how the spectrometer can avoid temperature determination errors in systems where thermal emission is accompanied by atomic or molecular emission lines.

Recent developments in time-of-flight PET.

While the first time-of-flight (TOF)-positron emission tomography (PET) systems were already built in the early 1980s, limited clinical studies were acquired on these scanners. PET was still a research tool, and the available TOF-PET systems were experimental. Due to a combination of low stopping power and limited spatial resolution (caused by limited light output of the scintillators), these systems could not compete with bismuth germanate (BGO)-based PET scanners. Developments on TOF system were limited for about a decade but started again around 2000. The combination of fast photomultipliers, scintillators with high density, modern electronics, and faster computing power for image reconstruction have made it possible to introduce this principle in clinical TOF-PET systems. This paper reviews recent developments in system design, image reconstruction, corrections, and the potential in new applications for TOF-PET. After explaining the basic principles of time-of-flight, the difficulties in detector technology and electronics to obtain a good and stable timing resolution are shortly explained. The available clinical systems and prototypes under development are described in detail. The development of this type of PET scanner also requires modified image reconstruction with accurate modeling and correction methods. The additional dimension introduced by the time difference motivates a shift from sinogram- to listmode-based reconstruction. This reconstruction is however rather slow and therefore rebinning techniques specific for TOF data have been proposed. The main motivation for TOF-PET remains the large potential for image quality improvement and more accurate quantification for a given number of counts. The gain is related to the ratio of object size and spatial extent of the TOF kernel and is therefore particularly relevant for heavy patients, where image quality degrades significantly due to increased attenuation (low counts) and high scatter fractions. The original calculations for the gain were based on analytical methods. Recent publications for iterative reconstruction have shown that it is difficult to quantify TOF gain into one factor. The gain depends on the measured distribution, the location within the object, and the count rate. In a clinical situation, the gain can be used to either increase the standardized uptake value (SUV) or reduce the image acquisition time or administered dose. The localized nature of the TOF kernel makes it possible to utilize local tomography reconstruction or to separate emission from transmission data. The introduction of TOF also improves the joint estimation of transmission and emission images from emission data only. TOF is also interesting for new applications of PET-like isotopes with low branching ratio for positron fraction. The local nature also reduces the need for fine angular sampling, which makes TOF interesting for limited angle situations like breast PET and online dose imaging in proton or hadron therapy. The aim of this review is to introduce the reader in an educational way into the topic of TOF-PET and to give an overview of the benefits and new opportunities in using this additional information.

Silicon photomultiplier readout of a monolithic 270×5×5 cm3 plastic scintillator bar for time of flight applications

The detection of 200–1000MeV neutrons requires large amounts, ~100cm, of detector material because of the long nuclear interaction length of these particles. In the example of the NeuLAND neutron time-of-flight detector at FAIR, this is accomplished by using 3000 monolithic scintillator bars of 270×5×5cm3 size made of a fast plastic. Each bar is read out on the two long ends, and the needed time resolution of σt<150ps is reached with fast timing photomultipliers. In the present work, it is investigated whether silicon photomultiplier (SiPM) photosensors can be used instead. Experiments with a picosecond laser system were conducted to determine the timing response of the assembly made up of SiPM and preamplifier. The response of the full system including also the scintillator was studied using 30MeV single electrons provided by the ELBE superconducting electron linac. The ELBE data were matched by a simple Monte Carlo simulation, and they were found to obey an inverse-square-root scaling law. In the electron beam tests, a time resolution of σt=136ps was reached with a pure SiPM readout, well within the design parameters for NeuLAND.

Pulse height tests of a large diameter fast LaBr3:Ce scintillation detector

The pulse height response of a large diameter fast 100mm×100mm LaBr3:Ce detector was measured for 0.1–10MeV gamma-rays. The detector has a claimed time resolution of 608ps for 511keV gamma rays, but has relatively poor energy resolution due to the characteristics of its fast photomultiplier. The detector pulse height response was measured for gamma rays from cobalt, cesium, and bismuth radioisotope sources as well as prompt gamma rays from thermal neutron capture in water samples contaminated with mercury (3.1wt%), boron (2.5wt%), cadmium (0.25wt%), chromium (52wt%), and nickel (22wt%) compounds. The energy resolution of the detector was determined from full width at half maximum (FWHM) of element-characteristic gamma ray peaks in the pulse height spectrum associated with the element present in the contaminated water sample. The measured energy resolution of the 100mm×100mm detector varies from 12.7±0.2% to 1.9±0.1% for 0.1 to 10MeV gamma rays, respectively. The graph showing the energy resolution ΔE/E(%) versus 1/√Eγ was fitted with a linear function to study the detector light collection from the slope of the curve. The slope of the present 100mm×100mm detector is almost twice as large as the slope of a similar curve of previously published data for a 89mm×203mm LaBr3:Ce detector. This indicates almost two times poorer light collection in the 100mm×100mm detector as compared to the other detector.