Large Photomultiplier Tubes Research Articles

Optimization of the Pixel Design for Large Gamma Cameras Based on Silicon Photomultipliers.

Most single-photon emission computed tomography (SPECT) scanners employ a gamma camera with a large scintillator crystal and 50-100 large photomultiplier tubes (PMTs). In the past, we proposed that the weight, size and cost of a scanner could be reduced by replacing the PMTs with large-area silicon photomultiplier (SiPM) pixels in which commercial SiPMs are summed to reduce the number of readout channels. We studied the feasibility of that solution with a small homemade camera, but the question on how it could be implemented in a large camera remained open. In this work, we try to answer this question by performing Geant4 simulations of a full-body SPECT camera. We studied how the pixel size, shape and noise could affect its energy and spatial resolution. Our results suggest that it would be possible to obtain an intrinsic spatial resolution of a few mm FWHM and an energy resolution at 140 keV close to 10%, even if using pixels more than 20 times larger than standard commercial SiPMs of 6 × 6 mm2. We have also found that if SiPMs are distributed following a honeycomb structure, the spatial resolution is significantly better than if using square pixels distributed in a square grid.

Afterpulse measurement of JUNO 20-inch PMTs

In this study, we present the large photomultiplier tube (PMT) afterpulse measurement results obtained from the Jiangmen underground neutrino observatory (JUNO) experiment. A total of 11 dynode-PMTs (R12860) from the Hamamatsu company (Hamamatsu Photonics K.K. (HPK)) and 150 micro-channel plate PMTs (MCP-PMTs, GDB-6201) from the NNVT company (North Night Vision Technology Co., Ltd. (NNVT)) were tested. Subsequently, an afterpulse model was built according to the afterpulse time distribution and the probability of occurrence for these two types of PMTs. The average ratio of the total afterpulse charge with a delay between 0.5 \(\upmu\)s and 20 \(\upmu\)s to the primary pulse charge is \(\sim\) 5.7% (13.2%) for the tested MCP-PMTs (dynode-PMTs). The JUNO experiment will deploy 20,012 20-inch PMTs; this study will benefit detector simulation, event reconstruction, and data analysis regarding the JUNO experiment.

The JUNO large PMT readout electronics

The Jiangmen Underground Neutrino Observatory (JUNO) is a large neutrino detector currently under construction in China. Thanks to the tight requirements on its optical and radio-purity properties, it will be able to perform leading measurements detecting terrestrial and astrophysical neutrinos in a wide energy range from tens of keV to hundreds of MeV. A key requirement for the success of the experiment is an unprecedented 3% energy resolution, guaranteed by its large active mass and the use in the central detector of more than 17,000 20-inch photomultiplier tubes (PMTs) acquired by high-speed, high-resolution sampling electronics located very close to the PMTs. In this contribution, the design of the Front-End and Read-Out electronics will be presented, together with the performances measured on prototype modules and during the mass production of the final electronics.

Study of Using Machine Learning for Level 1 Trigger Decision in JUNO Experiment

A study on the use of a machine learning algorithm for the level 1 trigger decision in the JUNO experiment ispresented. JUNO is a medium baseline neutrino experiment in construction in China, with the main goal of determining the neutrino mass hierarchy. A large liquid scintillator (LS)volume will detect the electron antineutrinos issued from nuclear reactors. The LS detector is instrumented by around 20000 large photomultiplier tubes. The hit information from each PMT will be collected into a center trigger unit for the level 1 trigger decision. The current trigger algorithm used to select a neutrino signal event is based on a fast vertex reconstruction. We propose to study an alternative level 1 (L1) trigger in order to achieve a similar performance as the vertex fitting trigger but with less logic resources by using firmware implemented machine learning model at the L1 trigger level. We treat the trigger decision as a classification problem and train a Multi-Layer Perceptron (MLP)model to distinguish the signal events with an energy higher than a certain threshold from noise events. We use JUNO software to generate datasets which include 100K physics events with noise and 100K pure noise events coming from PMT dark noise.For events with energy higher than 100 keV, the L1 trigger based on the converged MLP model can achieve an efficiency higher than 99%. After the training performed on simulations,we successfully implemented the trained model into a Kintex 7FPGA. We present the technical details of the neural network development and training, as well as its implementation in the hardware with the FPGA programming. Finally the performance of the L1 trigger MLP implementation is discussed.

A first prototype of C[formula omitted]D[formula omitted] total-energy detector with SiPM readout for neutron capture time-of-flight experiments

Low efficiency total-energy detectors (TEDs) are one of the main tools for neutron capture cross section measurements utilizing the time-of-flight (TOF) technique. State-of-the-art TEDs are based on a C6D6 liquid-scintillation cell optically coupled to a fast photomultiplier tube. The large photomultiplier tube represents yet a significant contribution to the so-called neutron sensitivity background, which is one of the most conspicuous sources of uncertainty in this type of experiments. Here we report on the development of a first prototype of a TED based on a silicon-photomultiplier (SiPM) readout, thus resulting in a lightweight and much more compact detector. Apart from the envisaged improvement in neutron sensitivity, the new system uses low voltage (+28 V) and low current supply (∼50 mA), which is more practical than the ∼kV supply required by conventional photomultipliers. One important difficulty hindering the earlier implementation of SiPM readout for this type of detector was the large capacitance for the output signal when all pixels of a SiPM array are summed together. The latter leads to long pulse rise and decay times, which are not suitable for time-of-flight experiments. In this work we demonstrate the feasibility of a Schottky-diode multiplexing readout approach, that allows one to preserve the excellent timing properties of SiPMs, hereby paving the way for their implementation in future neutron TOF experiments.

Energy resolution experiments of conical organic scintillators and a comparison with Geant4 simulations

An increase in light-collection efficiency (LCE) improves the energy resolution of scintillator-based detection systems. An improvement in energy resolution can benefit detector performance, for example by lowering the measurement threshold and achieving greater accuracy in light-output calibration. This work shows that LCE can be increased by modifying the scintillator shape to reduce optical-photon reflections, thereby decreasing transmission and absorption likelihood at the reflector boundary. The energy resolution of four organic scintillators (EJ200) were compared: two cones and two right-circular cylinders, all with equal base diameter and height (50 mm). The sides of each shape had two surface conditions: one was polished and the other was ground. Each scintillator was coupled to the center of four photomultiplier tube (PMT) configurations of different diameters. The photocathode response of all PMTs was assessed as a function of position using a small cube (5 mm height) of EJ200. The worst configuration, a highly polished conical scintillator mated to a PMT of equal base diameter, produced a smeared energy spectrum. The cause of spectrum smearing is explored in detail. Results demonstrate that a ground cone had the greatest improvement in energy resolution over a ground cylinder by approximately 16.2% at 478 keVee, when using the largest diameter (127 mm) PMT. This result is attributed to the greater LCE of the cone, its ground surface, and the uniform photocathode response near center of the largest PMT. Optical-photon transport simulations in Geant4 of the cone and cylinder assuming a diffuse reflector and a uniform photocathode were compared to the best experimental configuration and agreed well. If a detector application requires excellent energy resolution above all other considerations, a ground cone on a large PMT is recommended over a cylinder.

Sequential Detection for Optical Wireless Scattering Communication

In an optical wireless scattering communication network, the receiver needs to periodically listen to the channel to detect whether the channel is occupied by other transceiver pairs. It falls into the spectrum sensing category of the cognitive radio. In this work, we adopt sequential detection for the spectrum sensing, for both a photon-counting receiver and a photomultiplier tube (PMT) receiver. For the PMT receiver, to reduce the computational complexity, we propose a one-term approximation for the log-likelihood ratio (LLR) computation. We also extend the sequential detection to cooperative sensing with multiple photon-counting and PMT receivers. From the simulations, it is seen that the one-term approximation can show a comparable number of samples as that for the exact LLR computation to achieve certain miss detection and false alarm probabilities, significantly fewer than those required by the Gaussian approximation for a low PMT amplification factor. The numbers of samples for both the Gaussian and one-term approximations are close to those for the exact LLR computation for a large PMT amplification factor.

Suppressing ringing caused by large photomultiplier tube signals

We describe here the characteristic features of the ringing we observed following large PMT signals in the Daya Bay reactor antineutrino experiment. We conclude that the ceramic capacitors used in the circuitry of the PMT bases and the HV-signal decouplers are the primary cause for this ringing. We present some possible schemes to reduce the ringing when replacing these ceramic capacitors is not feasible.

Multi-PMT optical module for the KM3NeT neutrino telescope

The future cubic kilometre scale neutrino telescope KM3NeT will employ a novel type of a Digital Optical Module (DOM), developed during the recent FP6 Design Study. A pressure-resistant glass sphere hosts 31 photomultiplier tubes (PMTs) of 3-in. diameter, together with all the electronics for high-voltage generation and signal readout. The optical module forms a complete stand-alone detector that is connected to the outside world via a single optical fibre and two copper conductors providing electrical power. The advantages of using multiple small PMTs in the same DOM are the higher quantum efficiency (>30% expected), smaller transit time spread, better two-photon separation capability and directional sensitivity. Moreover, a longer operating lifetime is expected than for large PMTs due to the accumulation of less charge on the anode. In addition, small PMTs are insensitive to the Earth's magnetic field and do not require μ-metal shielding. In order to maximise the detector sensitivity, each PMT will be surrounded by an expansion cone collecting photons that would normally miss the photocathode. Such an expansion cone consists of an aluminium ring filled with silicone gel. An increase in the overall sensitivity, integrated over all angles of incidence, was estimated to be about 27%. Monte-Carlo simulations have shown that a detector configuration with multi-PMT DOMs requires three times less OMs to achieve the same performance as conventional OMs hosting 10-in. PMTs. Prototype DOMs are currently being built by the KM3NeT consortium.

Performance of the front-end electronics of the ANTARES neutrino telescope

ANTARES is a high-energy neutrino telescope installed in the Mediterranean Sea at a depth of 2475m. It consists of a three-dimensional array of optical modules, each containing a large photomultiplier tube. A total of 2700 front-end ASICs named analogue ring samplers (ARS) process the phototube signals, measure their arrival time, amplitude and shape as well as perform monitoring and calibration tasks. The ARS chip processes the analogue signals from the optical modules and converts information into digital data. All the information is transmitted to shore through further multiplexing electronics and an optical link. This paper describes the performance of the ARS chip; results from the functionality and characterization tests in the laboratory are summarized and the long-term performance in the apparatus is illustrated.

Simulation of large photomultipliers for experiments in astroparticle physics

We have developed an accurate simulation model of the large 9 in. photomultiplier tubes (PMT) used in water-Cherenkov detectors of cosmic-ray induced extensive air-showers. This work was carried out as part of the development of the Off ¯ line ̲ simulation software for the Pierre Auger Observatory surface array, but our findings may be relevant also for other astrophysics experiments that employ similar large PMTs. The implementation is realistic in terms of geometrical dimensions, optical processes at various surfaces, thin-film treatment of the photocathode, and photon reflections on the inner structure of the PMT. With the quantum efficiency obtained for this advanced model we have calibrated a much simpler and a more rudimentary model of the PMT which is more practical for massive simulation productions. We show that the quantum efficiency declared by manufactures of the PMTs is usually determined under conditions substantially different from those relevant for the particular experiment and thus requires careful (re)interpretation when applied to the experimental data or when used in simulations. In principle, the effective quantum efficiency could vary depending on the optical characteristics of individual events.

Testing of photomultiplier tubes for use in the surface detector of the Pierre Auger observatory

In the array of water Cherenkov detectors of the Pierre Auger Observatory, 4800 large photomultiplier tubes (PMTs) will be used. Before being deployed, each PMT is evaluated to check that various parameters, such as the linearity, dark noise, and gain, fall within a specified range. The large scale test system, designed and constructed for this purpose, is capable of testing multiple large PMTs simultaneously. The test system and the results of the tests for the first 3964 PMTs are presented in this paper.

Design evaluation of A-PET: A high sensitivity animal PET camera

In recent years it has been shown that PET is capable of obtaining in vivo metabolic images of small animals. These serve as models to study the development and progress of diseases within humans. Imaging small animals requires not only image resolution better than 2 mm, but also high sensitivity in order to image ligands with low specific activity or radiochemical yields. Toward achieving these goals, we have developed a discrete 2 /spl times/ 2 /spl times/ 10 mm/sup 3/ GSO Anger-logic detector for use in a high resolution, high sensitivity, and high count-rate animal PET scanner. This detector uses relatively large 19 mm diameter photomultiplier tubes (PMT), but nevertheless achieves good spatial and energy resolution. The scanner (A-PET) has a port diameter of 21 cm, transverse field-of-view of 12.8 cm, axial length of 11.6 cm, and operates in 3-D volume imaging mode. The absolute coincidence sensitivity is 1.3% for a point source. Due to the use of large PMTs in an Anger design, the encoding ratio (number of crystals/PMT) is high, which reduces the complexity and leads to a cost-effective scanner. Simulation results show that this scanner can achieve high NEC rates for small cylindrical phantoms due to its high sensitivity and low dead-time. Initial measurements show that our design goals for spatial resolution and sensitivity were realized in the prototype scanner.

A systematic study of large PMTs for the Pierre Auger Observatory

In order to select the most suitable Photomultiplier Tubes (PMTs) for the surface detectors of the Pierre Auger Observatory, we have performed extensive tests on large PMTs from three different manufacturers: Electron Tubes Limited, Hamamatsu Photonics, and Photonis Imaging Sensors. The test and their results are described in this report.

A systematic study of large PMTs for the Pierre Auger Observatory

In order to select the most suitable Photomultiplier Tubes (PMTs) for the surface detectors of the Pierre Auger Observatory, we have performed extensive tests on large PMTs from three different manufacturers: Electron Tubes Limited, Hamamatsu Photonics, and Photonis Imaging Sensors. The test and their results are described in this report.

The application of the curved-grid technique to a gas proportional scintillation counter with a small-diameter photo-multiplier tube

The curved-grid technique was developed to maintain the superior performance of large-area gas proportional scintillation counters (GPSCs) without resorting to complex and bulky focusing systems or large photomultiplier tubes (PMTs) for applications in energy-dispersive X-ray fluorescence analysis. The technique is a simple method to compensate for the variation in solid angle viewed by the PMT as a function of the radial distance from the cylindrical axis of the detector. The feasibility of the technique is demonstrated in a GPSC, by measuring the energy resolution as a function of entrance window diameter. With a properly shaped curved grid, no degradation in detector energy resolution is observed even when the effective detector sensitive area is increased approximately six-fold. The maximum ratio of detector entrance window to PMT diameter achieved thus far is approximately 0.75.

Colliding plasma neutron production at Trident

Trident is a two-beam Nd:glass laser producing typically 100 J at 2ω in 2 ns pulses. Diffraction unlimited f/6 optics reduce the 20-cm-diam beams down to 100 μm diameter. The laser is capable of producing neutrons from D-D and D-T plasmas, and has demonstrated yields of >106 D-D neutrons from colliding plasma geometries. We have combined a previously existing neutron activation technique with two large photomultiplier tubes (PMTs) coupled to scintillators to produce a neutron measuring capability on Trident. In addition, we have coupled a time-of-flight compensated scintillator to a fast microchannel plate PMT to provide neutron energy resolution and hence the potential to measure ion temperatures through time-of-flight spread. The activation technique is sensitive to >105 neutrons per count in its present configuration. The PMT/scintillators have comparable sensitivities. The MCP/PMT/scintillator combination has 220 ps rise time with an order of magnitude less sensitivity. We will describe these detectors and the methods used to calibrate the individual detector sensitivities.

Light concentrators for the Sudbury Neutrino Observatory

Abstract There is an important and growing class of elementary particle detectors which are characterized by a large sensitive volume (thousands of tonnes), very low radioactive backgrounds, and rely on the emission of light for particle detection. Water Cherenkov detectors come into this category; they have a large mass of water as the sensitive medium. Particles are detected when they interact with the water and produce Cherenkov light, so detection efficiency relies on having a huge light sensitive area at the periphery of the detector. The most cost-effective way of achieving this is by placing light concentrators on large photomultiplier tubes (PMTs). This paper describes the work carried out on light concentrators for the PMTs in the Sudbury Neutrino Observatory, a 1000 tonne heavy water Cherenkov detector. We discuss the advantages of using light concentrators, summarize the optical theory of non-imaging light concentration, and describe in detail the development and manufacture of the concentrators themselves.

Recent Developments in Detectors for High Spatial Resolution Positron CT

Experiments using three types of detectors for high spatial resolution positron CT have been carried out as follows : 1. One to one coupling between a BGO scintillator and a thin rectangular photomultiplier tube (PMT). 2. Combining a small position sensing PMT with two BGO scintillators. 3. Combining a large PMT with two or more BGO scintillators and using other detectors for scintillator identification -- a) small PMT's, b) silicon photodiodes (SiPD). The time resolution obtained in method 1 was poorer than that of the other methods due to the present status of thin PMT performance - poor cathode sensitivity. In method 2 and 3-a), good time resolution and position sensing were obtained. In method 3-b), the peak to valley ratio of 1.8 in pulse height spectrum was obtained with a cooled BGO scintillator and a SiPD.

A liquid scintillation detector for evaluating phototubes and determining gamma-ray activities

The design and operating characteristics of a liquid scintillation test tank for evaluating large photomultiplier tubes are described. The detector tank was a 16 in. diameter by 6 1 2 - in. deep cylinder filled with PPO and POPOP in toluene and mounted with a 16-in. photomultiplier tube. The half resolution of the Cs 137 Compton “peak” for the system was 29.9 percent. Counting sensitivity for typical γ-emitters were 62 pc/ml for Cs 137, 27 pc/ml for Co 60, and 11 pc/ml for Zn 65 based a 5-min count of 0.25 1. samples and a 1 percent counting error. Detector response to a collimated photon beam was found to be uniform over the surface of the detector tank, falling off only at the edges of the tank 9.5 percent. Counting efficiencies up to 23.2 percent were obtained for a point source of Cs 137. Thistype of detector is extremely useful in testing individual 16-in. phototubes of the type used in whole-body counters. Such a “test tank” permits individual focusing of the tube, noise level determination, determination of resolution, and determination of uniformity of photocathode response prior to the installation of the tube in a whole-body counting facility. In addition, the test tank system itself may be used as a sensitive γ-detection system.