Photomultiplier Tube Research Articles

Synergistic Effect of Surface States and Deep Defects for Ultrahigh Gain Deep‐Ultraviolet Photodetector with Low‐Voltage Operation

AbstractTo achieve ultra‐high gain deep‐ultraviolet (DUV) detectors based on ultra‐wide bandgap semiconductors comparable with those of bulky photomultiplier tubes (PMTs), avalanche photodiodes have usually been adopted. However, the high‐operation voltage (∼100 V) is not compatible with monolithic integration. Herein, it is demonstrated that the ultra‐high gain DUV photodetectors (PDs) with low operation voltages (<5 V) can be achieved by using the synergistic effect of surface states and deep defects in a type‐Ib single‐crystal diamond (SCD) substrate. The overall photoresponse, such as the sensitivity, dark current, spectral selectivity, and response speed, of the diamond DUV‐PDs can be simply tailored by the surface hydrogen or oxygen termination of the SCD substrate. The DUV responsivity and external quantum efficiency are more than 2.5 × 104A/W and 1.4 × 107%, respectively, at 220 nm‐wavelength light, comparable with those of PMTs. The DUV/visible light rejection ratio (R220 nm/R400 nm) is as high as 6.7 × 105. The depletion of the 2D hole gas by deep nitrogen defect provides a low dark current and the filling of the ionized nitrogen upon DUV illumination induces a huge photocurrent. The synergistic effect of the surface states and the bulk deep defects opens the avenue for the development of DUV detectors compatible with integrated circuits.

Performance of an LAPPD in magnetic fields

Magnetic fields affect the response of Micro-Channel Plate (MCP)-based detectors, although the effect is smaller than that for conventional photo-multiplier tubes. The main effect of the field is a reduction in gain and efficiency.In this article, we report our studies of the effects of the magnetic field on the Large Area Picosecond PhotoDetectors (LAPPDs), photosensors of large sensitive area based on MCP technology. The LAPPD under study was the most recent, short stack, 10μm pore model, expected to have the best capabilities to withstand magnetic field distortions. The measurements were performed at CERN on the MNP-17 and M113 vertical dipole magnets in magnetic fields up to ∼ 1.5 T. The results show the exponential drop of the LAPPD gain as a function of the magnetic field strength, with a rather mild dependence on the angular distribution. The relative photon detection efficiency in magnetic field is also affected. However, both the gain and the efficiency can be partially recovered by increasing the LAPPD bias voltages. Geometrical effects on the anode charge spot and time resolution were also studied.

Study of Signal Pattern Recognition and Predictive Maintenance in Liquid Scintillators and Photomultiplier Tube

Study of Signal Pattern Recognition and Predictive Maintenance in Liquid Scintillators and Photomultiplier Tube

Structural modification of MgO/Au thin films by aluminum Co-doping and related studies on secondary electron emission

The secondary electron emission (SEE) has the potential applications in electron multiplication, mass spectrometer, scanning electron microscope, photomultiplier tubes and so on. Among these, the electron multiplier (EM) based on MgO/Au thin film has attracted great attention over the past few years. Here, we design a new kind of MgO thin film by co-doping of gold and aluminum elements based on the structural modification through reactive magnetron sputtering method. The doping of Al into MgO/Au film gives a rise to the maximum SEE coefficient (δmax) between 9.02 and 10.23 while the optimal decay rate is around 10.4 % after 2 h of consistent electron bombardment. Herein, we also improved the stability of the film stored in air by sputtering Al2O3 layer on it. For the sample sputtered with the protecting layer Al2O3, its SEE coefficient (δ) at the incident electron energy of 200 eV still kept at a relatively high level that exceed 4.5 after stored in air for 72 h. The film properties after Al and Au co-doping are investigated in detail by the SEM, AFM, XPS and UV-VIS spectroscopy. Our results provide a new candidate for SEE layer in the application of long lifespan vacuum electron devices.

An accurate semi-empirical model for PMT pulse signal analysis.

The energy information of pulse signals is significantly important for applications such as computed tomography (CT), positron emission tomography (PET), and research on defects in condensed matter. Time-over-threshold (TOT) and multi-voltage threshold (MVT) are commonly used digitization methods in sampling pulse signal. However, both approaches rely on a mathematical model of the pulse signal to derive energy information. This study proposes a semi-empirical mathematical model for pulse signals formation process in scintillation crystal-coupled photomultiplier tube(PMT) probes, by utilizing the CR-RC shaping method. This mathematical model accurately describes output of the PMT pulse signals. This study analyzes a substantial dataset of pulse signals, comparing the performance of the newly designed mathematical model with that of the double exponential function in terms of their ability to fit pulse signals. The results indicate that the mathematical model developed herein achieves an average R2 of 0.9255, significantly surpassing the 0.9155 of the double exponential function, thereby demonstrating its superior fitting efficacy.

Installation and commissioning of the Electromagnetic Calorimeter in the HADES experiment

The Electromagnetic Calorimeter (ECAL) was fully installed and commissioned in 2023 as a part of the HADES experiment at FAIR-GSI, Germany. HADES is a versatile magnetic spectrometer designed to study medium modifications of light vector mesons through their dilepton decay in heavy-ion collisions and to explore the QCD phase diagram at high baryonic densities and low temperatures. The ECAL setup comprises six sectors with 163 modules each, using Cherenkov light detection with lead-glass prisms and photomultiplier tubes. Preliminary results from the π0 invariant mass reconstruction during the C+C 800 A MeV HADES experiment in February 2024 are presented.

Effects of the passive voltage divider in a photomultiplier tube: Analytical model, simulations and experimental validation

The effects of the passive resistive voltage divider network in a photomultiplier tube (PMT) have been investigated by developing an in-house Monte Carlo simulation code and compared with experimental measurements and an analytical model. The simulation code follows an iterative procedure that takes into account the transport and amplification of the electrons within the device depending on the electrostatic fields produced by the electrode voltages. The PMT gain, dynode voltages, rise time and transit time have been studied as a function of the photocathode current and supply voltage. A good agreement between the analytical model, the simulations and numerous experimental measurements using a Hamamatsu R13408-100 PMT has been obtained. The simulation results endorse the use of logistic functions within the analytical model to account for the collection efficiency in the last dynode stages. This works deepens the understanding of passive voltage dividers and develops an advanced behavioral circuit model of photomultiplier tubes. Although validated for a single PMT, the proposed methodology is applicable to any PMT model. This aids in optimizing the design of fully active voltage dividers, to be applied in extremely pulsed applications with high count rates such as prompt gamma-ray imaging during proton therapy.

Elucidation of FDG-PET Imaging Characteristics that Reflect the Heterogeneity within Tumors Due to Variability in Metabolic Activity: A Phantom Study

Abstract Objective Focusing on the heterogeneity within cancer lesions and revealing cancer lesions with a high signal-to-noise ratio will help improve the quality of positron emission tomography (PET) images. This study aimed to understand how glucose metabolic activity can be shown with less statistical noise using a quality assessment phantom modeled after cancer lesions with a two-layer structure and a Clear adaptive Low-noise Method (CaLM) filter. Materials and Methods A National Electrical Manufacturers Association phantom with two spheres with a two-layer structure filled with 2-deoxy-2[18F]fluoro-D-glucose (inner and outer diameters of the spheres were 13/22 and 22/37 mm, respectively; radioactivity ratio of the background [BG] to outer sphere layer was 1:4; and BG-to-inner sphere layer ratios were 1:1, 1:2, and 1:3) was evaluated. The acquisition time was set at 120 seconds, and imaging was repeated five times. The image data in photomultiplier tube (PMT)-PET were reconstructed using a time-of-flight (TOF) ordered subset expectation maximization (OSEM) algorithm (point spread function [PSF] − , iteration: 3, subset: 10) with a 4-mm Gaussian filter (GF) for normal images. Silicon photomultiplier (SiPM)-PET data were reconstructed using a TOF OSEM algorithm (PSF − , iteration: 2, subset: 12) and a 3-mm GF for normal images. The target images were reconstructed using three CaLM parameters (mild, standard, and strong). All the obtained images were investigated quantitatively, with calculation of maximum standard uptake value (SUVmax), coefficient of variation (CV), and contrast-to-noise ratio (CNR), after setting regions of interest on the lesions. Statistical analysis using the Dunnett's test compared normal images (control group) and target images (treatment group). Statistical significance was considered at p < 0.05. Results Quantitative assessment revealed that the SUVmax of target images (standard and strong) was equivalent to that of normal images in PMT-PET, with SUVmax of 3 to 3.5 for both layers. The SUVmax in SiPM-PET was similar across all CaLM types, ranging from 3 to 4 for all spheres. The target images (standard and strong) had a significantly reduced CV and improved CNR compared with normal images. Conclusion The boundary of the 22/37-mm spheres was visible with CaLM (strong) at radioactivity ratios of 1:4:1 and 1:4:2 on both scanners. For the 13/22-mm sphere boundary, visibility with CaLM (strong) was observed only with SiPM-PET, with the SUVmax equivalent to normal images. CaLM (strong) was deemed the optimal postprocessing filter for PMT-PET due to significant improvements in CV and CNR, while CaLM (standard) was suggested as the optimal filter for SiPM-PET due to excessive BG smoothing.

Development of α-ray visualization survey meter in high gamma and neutron background environment.

A survey meter was developed to reliably detect and visualize surface contamination of suits and objects by α-nuclides in high γ/n-rays background radiation environment. The survey meter features a semi-opaque ZnS:Ag scintillator mounted directly onto a multi-anode photomultiplier tube (MA-PMT) and amplification circuits, ensuring output gain equalization for all channels. α-ray events induce localized light emission in thin-film scintillators. By directly mounting the scintillator, diffusion of light before reaching the MA-PMT is suppressed, concentrating it in just a few channels, thereby facilitating discrimination from background radiation. This design also enables clear visualization of the shape of surface contamination. The prototyped survey meter is capable of responding up to 2.1×107cpm, with no γ-ray response even in high-radiation environments exceeding 1Sv/h. In actual environments with high background radiation, contamination of ~1/100th of the surface contamination density limit of 4Bq/cm2 could be reliably detected.

TMM: Triple Micro-Mesh gaseous structure with ultralow ion backflow for gaseous photon detectors

Gaseous photomultiplier tubes sensitive to visible light and based on micro-pattern gaseous detectors have been widely investigated due to their wide range of potential applications. This study presents a novel triple micro-mesh gaseous structure (TMM) specifically designed for this purpose, featuring ultralow ion backflow (IBF). Prototypes of the TMM were manufactured and characterized with both an X-ray source and an ultraviolet laser, and the results demonstrated an unprecedented IBF ratio of 3 × 10−5 at gas gains exceeding 1 × 105, indicating a promising capability of TMMs for visible light detection.

Comprehensive analysis of beryllium content influence on secondary electron yield in Cu[sbnd]Be alloys

This study examines the impact of varying Be contents on the evolution of secondary electron emission (SEE) properties. Through microscopic characterization of the microstructure before and after activation, it was determined that the phase composition was α(Cu) phase and eutectic structure (α(Cu) + γ). The findings indicate that as the Be content increased from 2.8 wt% to 3.8 wt%, the proportion of heterogeneous structures increased and the distribution became more uniform. Meanwhile, the number of heterogeneous structure interfaces between α(Cu) phase and γ phase increased, and there were a large number of mismatch dislocations at the interfaces, which served as short-circuit diffusion paths for Be elements. Be elements were more easily able to diffuse outward through the interface to form a uniform BeO film, thereby increasing secondary electron yield (SEY). In addition, the density of mismatch dislocations near the interface was high, promoting the formation of grain boundaries, which provided more diffusion pathways, allowing Be elements to diffuse outward more easily, thereby generating a uniform BeO film with increased SEY. This study holds significant implications for augmenting the SEY of CuBe dynode electrodes used in photomultiplier tubes (PMTs).

Effect of temperature on the scintillation properties of pure LaCl3 and Cs2LiYCl6:Ce crystals for neutron spectroscopy

The Lunar Vehicle Radiation Dosimeters (LVRAD) project, run by the Korea Astronomy and Space Science Institute, is currently in the detector R&D phase. Its mission is to measure the radiation exposure experienced by astronauts on the lunar surface and to search for water and radioactive isotopes. This study focuses on inorganic scintillator R&D for neutron spectroscopy, which is essential for the LVRAD project. Two candidates, pure LaCl3 and Cs2LiYCl6:Ce enriched with 95% 6Li (CLYC-6) detectors, were investigated in this work. Though their neutron spectroscopy performance meets radiation hardness requirements, the temperature-dependent performance of the detectors needs to be clearly understood to ensure reliable operation in space. Therefore, the performance of pure LaCl3 and CLYC-6 detectors was investigated for working temperatures ranging from -30∘C to +50∘C. The dimensions of the scintillators used for measurements were Φ1.5 inch × 1.0 inch for pure LaCl3 and Φ1.5 inch × 1.5 inches for CLYC-6. Scintillation performance was measured using a Hamamatsu H7195 photomultiplier tube with a 500 MHz flash analog-to-digital converter. The detectors were operated in a large temperature and humidity chamber across a temperature range from -30∘C to +50∘C, and the temperature dependence of the pulse shape discrimination performance for fast and thermal neutrons was measured using pure LaCl3 and CLYC-6, respectively. The effect of the temperature on the absolute light yield, energy resolution, and decay times was also measured. Based on the results, the pure LaCl3 and CLYC-6 detectors proved suitable for neutron spectroscopy for the LVRAD project.

Enhancing the light yield of He:CF4 based gaseous detector

The CYGNO experiment aims to build a large (O(10) m3) directional detector for rare event searches, such as nuclear recoils (NRs) induced by dark matter (DM), such as weakly interactive massive particles (WIMPs). The detector concept comprises a time projection chamber (TPC), filled with a He:CF4 60/40 scintillating gas mixture at room temperature and atmospheric pressure, equipped with an amplification stage made of a stack of three gas electron multipliers (GEMs) which are coupled to an optical readout. The latter consists in scientific CMOS (sCMOS) cameras and photomultipliers tubes (PMTs). The maximisation of the light yield of the amplification stage plays a major role in the determination of the energy threshold of the experiment. In this paper, we simulate the effect of the addition of a strong electric field below the last GEM plane on the GEM field structure and we experimentally test it by means of a 10 × 10 cm2 readout area prototype. The experimental measurements analyse stacks of different GEMs and helium concentrations in the gas mixture combined with this extra electric field, studying their performances in terms of light yield, energy resolution and intrinsic diffusion. It is found that the use of this additional electric field permits large light yield increases without degrading intrinsic characteristics of the amplification stage with respect to the regular use of GEMs.

Research on Rate Adaptation of Underwater Optical Communication with Joint Control of Photoelectric Domain

As the communication distance changes, the received signal strength of an underwater optical communication system will change, and the range of its variation may not only exceed the dynamic range of the photoelectric detection device but also cause the reliability of communication to change due to the change in the received signal-to-noise ratio. In order to maintain better communication over a longer distance, this paper proposes a rate-adaptive method for underwater optical communication with joint control in the photoelectric domain. In the optical domain, the incident light’s power is adaptively adjusted by controlling the transmittance of the liquid crystal light valve to reduce saturation distortion. In the electrical domain, the constellation distribution is optimized according to the desired probability mass function, and the modulation order is adjusted in real time by estimating the received signal-to-noise ratio of the link. The simulation results show that under the forward error correction (FEC) threshold, the proposed method increases the dynamic range of the photomultiplier tube (PMT) by about 10 dB and expands the dynamic range of the system’s communication distance.

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.

Review of Photodetectors for Space Lidars

Photodetectors play a critical role in space lidars designed for scientific investigations from orbit around planetary bodies. The detectors must be highly sensitive due to the long range of measurements and tight constraints on the size, weight, and power of the instrument. The detectors must also be space radiation tolerant over multi-year mission lifetimes with no significant performance degradation. Early space lidars used diode-pumped Nd:YAG lasers with a single beam for range and atmospheric backscattering measurements at 1064 nm or its frequency harmonics. The photodetectors used were single-element photomultiplier tubes and infrared performance-enhanced silicon avalanche photodiodes. Space lidars have advanced to multiple beams for surface topographic mapping and active infrared spectroscopic measurements of atmospheric species and surface composition, which demand increased performance and new capabilities for lidar detectors. Higher sensitivity detectors are required so that multi-beam and multi-wavelength measurements can be performed without increasing the laser and instrument power. Pixelated photodetectors are needed so that a single detector assembly can be used for simultaneous multi-channel measurements. Photon-counting photodetectors are needed for active spectroscopy measurements from short-wave infrared to mid-wave infrared. HgCdTe avalanche photodiode arrays have emerged recently as a promising technology to fill these needs. This paper gives a review of the photodetectors used in past and present lidars and the development and outlook of HgCdTe APD arrays for future space lidars.

Divertor tungsten source monitoring by A visible spectroscopy diagnostic on EAST

EAST has been upgraded with top and bottom tungsten divertors to facilitate the high power long pulse operation. A visible spectroscopy diagnostic has been developed progressively to monitor W source as well as line emissions from other particles (e.g., D, He, Li, B, C, N, O, Ne, Ar, Mo, D2, WD) in the divertors. Two sets of lens installed in mid-plane port view tangentially the top and bottom divertors, respectively. Two types of optical fibers transfer the plasma light collected by the lens to three different detecting modules. High spectral resolution (λ/Δλ ∼ 14000) can be achieved by the detecting module consisting of spectrometer and Electron-Multiplying Charge Coupled Device (EMCCD), high temporal resolution (50 μs) is obtained by filtered photoelectric multiplier (PMT), and high spatial resolution (1 mm) is acquired by Complementary Metal-Oxide-Semiconductor Transistor (CMOS) camera with collimation optics. The multichannel optical fiber array with 500 μm core diameter is used to connect the lens and the first two detecting modules. The imaging fiber bundle with 30 μm core diameter transmits the two-dimensional divertor plasma light to the third detecting module, i.e. collimation optics and CMOS camera. The diagnostic is operated automatically in normal EAST discharges to support experimental operation and divertor physics study. The paper presents a technical description of the diagnostic and typical measurements during EAST discharges.

Scintillation light in SBND: simulation, reconstruction, and expected performance of the photon detection system

SBND is the near detector of the Short-Baseline Neutrino program at Fermilab. Its location near to the Booster Neutrino Beam source and relatively large mass will allow the study of neutrino interactions on argon with unprecedented statistics. This paper describes the expected performance of the SBND photon detection system, using a simulated sample of beam neutrinos and cosmogenic particles. Its design is a dual readout concept combining a system of 120 photomultiplier tubes, used for triggering, with a system of 192 X-ARAPUCA devices, located behind the anode wire planes. Furthermore, covering the cathode plane with highly-reflective panels coated with a wavelength-shifting compound recovers part of the light emitted towards the cathode, where no optical detectors exist. We show how this new design provides a high light yield and a more uniform detection efficiency, an excellent timing resolution and an independent 3D-position reconstruction using only the scintillation light. Finally, the whole reconstruction chain is applied to recover the temporal structure of the beam spill, which is resolved with a resolution on the order of nanoseconds.

Prediction of Energy Resolution in the JUNO Experiment

Abstract This paper presents the energy resolution study in the JUNO experiment, incorporating the latest knowledge acquired during the detector construction phase. The determination of neutrino mass ordering in JUNO requires an exceptional energy resolution better than 3% at 1 MeV. To achieve this ambitious goal, significant efforts have been undertaken in the design and production of the key components of the JUNO detector. Various factors affecting the detection of inverse beta decay signals have an impact on the energy resolution, extending beyond the statistical fluctuations of the detected number of photons, such as the properties of liquid scintillator, performance of photomultiplier tubes, and the energy reconstruction algorithm. To account for these effects, a full JUNO simulation and reconstruction approach is employed. This enables the modeling of all relevant effects and the evaluation of associated inputs to accurately estimate the energy resolution. The study reveals an energy resolution of 2.95% at 1 MeV. Furthermore, the study assesses the contribution of major effects to the overall energy resolution budget. This analysis serves as a reference for interpreting future measurements of energy resolution during JUNO data taking. Moreover, it provides a guideline in comprehending the energy resolution characteristics of liquid scintillator-based detectors. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Article funded by SCOAP3 and published under licence by Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Science and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd.

Long-Term Afterglow Measurement of Scintillators after Gamma Irradiation

The long-term afterglow of scintillators is an important aspect, especially when the light signal from a scintillator is evaluated in the current mode. Scintillators used for radiation detection exhibit an afterglow, which usually comes from multiple components that have different decay times. A high level of afterglow usually has a negative influence on the detection parameters for the energy resolution in spectrometry measurements or X-ray and neutron imaging. The paper deals with the long-term afterglow of some types of scintillators, which is more significant for integral measurement when the current is measured in a photodetector. The range of decay times studied was in the order of tens of seconds to days. Seven types of scintillators were examined: BGO, CaF2(Eu), CdWO4, CsI(Tl), LiI(Eu), NaI(Tl), and plastic scintillator. The scintillators were excited by gamma-ray radiation. After irradiation, the detection unit, along with the scintillator, was moved to a laboratory where the anode current of the photomultiplier tube was measured using a picoammeter for at least a day. The measurements showed that CdWO4 and plastic scintillators have relatively low long-term afterglow signals in comparison to the other scintillators studied.