Small Photomultiplier Tube Research Articles

AugerPrime status and prospects

The Pierre Auger Collaboration started a few years ago the AugerPrime project to increase the Surface Detector (SD) performance of the Pierre Auger Observatory. It aims to address the still open questions on the origin and composition of the highest energy cosmic rays by allowing a better identification of the nature of the primaries. The key element of this major upgrade is the capability of measuring the different components of extensive air showers, which will be significantly improved by the addition of a Surface Scintillator Detector (SSD) on each water-Cherenkov detector (WCD) constituting the SD. Moreover, the dynamic range of measurement is extended through an additional small photomultiplier tube inside the WCD. New electronics is processing the signals from the WCD and the SSD with higher sampling frequency and enhanced resolution. The scintillator module deployment started in 2019, and the new electronics in December 2020. The collected data allow for the evaluation of the first performances of the upgraded array and to adapt the whole data acquisition chain necessary for an efficient and sustainable operation of the Observatory. After the recall of the motivations for the upgrade, the main characteristics of the new detection setup are reviewed, as well as the status of its deployment and commissioning. The expected prospects are also discussed.

AugerPrime: The Pierre Auger Observatory upgrade

After more than 15 years of successful data taking, the Pierre Auger Observatory started a major upgrade, called AugerPrime, whose main aim is the collection of new information about the primary mass of ultrahigh-energy cosmic rays, besides adding new indications on hadronic interactions at energies much larger than those reached in human-made accelerators. The upgrade program includes: the installation of a plastic scintillator detector (SSD) and of a radio antenna on top of each water-Cherenkov detector (WCD) of the surface array, an extension of the dynamic range of measurement through an additional small photomultiplier tube inside the WCD, new electronics to process signals from the WCD and the SSD with higher sampling frequency and enhanced resolution in amplitude. An array of underground scintillator detectors will measure the muonic component of lower energy extensive air showers. After presenting the motivations for upgrading the Observatory, an overview of the detectors is provided, together with the deployment and commissioning status.

Development of a small and light portable positron annihilation lifetime measurement equipment for on-site measurements

Positron annihilation lifetime measurement has been a destructive analysis method in the sense that it requires cutting the specimen in two pieces, but the anti-coincidence method we developed enables the measurement of positron annihilation lifetime without cutting. In this study, by applying this anti-coincidence method, we developed a small and light portable positron annihilation lifetime measurement equipment for on-site measurements. In order to make the equipment small and light, we used a small photomultiplier tube for the γ-ray detectors, and we determined the detector configuration by simulation and experiment. To evaluate the performance of the developed equipment, we conducted positron annihilation lifetime measurements on shot-peened stainless steel and compared the results to those by the desktop anti-coincidence equipment. Just like the desktop equipment, the developed equipment revealed the increase in the defect density by shot-peening as the change in the positron lifetime, verifying the effectiveness of this equipment.

Design and calibration of the high energy particle monitor onboard the Insight-HXMT

Three high energy particle monitors (HPMs) employed onboard the Hard X-ray Modulation Telescope (Insight-HXMT) can detect the charged particles from South Atlantic Anomaly (SAA) and hence provide the alert trigger for switch-on/off of the main detectors. Here a typical design of HPM with high stability and reliability is adopted by taking a plastic scintillator coupled with a small photomultiplier tube (PMT). The window threshold of HPM is designed as 1 MeV and 20 MeV for the incident electron and proton, respectively. Before the launch of Insight-HXMT, we performed in details the ground calibration of HPM. The measured energy response and its dependence on temperature are taken as essential input of Geant4 simulation for estimating the HPM count rate given with an incident particle energy spectrum. This serves as a guidance for choosing a reasonable working range of the PMT high voltage once the real SAA count rate is measured by HPM in orbit. So far the three HPMs have been working in orbit for more than two years. Apart from providing reliable alert trigger, the HPMs data are used as well to map the SAA region.

In vivo evaluation of the effect of lithium on peripheral circadian clocks by real-time monitoring of clock gene expression in near-freely moving mice

Lithium has been used as a mood stabilizer to treat human bipolar disorders for over half a century. Several studies have suggested the possibility that the efficacy of lithium treatment results in part from the amelioration of circadian dysfunction. However, the effect of lithium on clock gene expression has not yet been investigated in vivo because continuous measurement of gene expression in organs with high time resolution over a period of several days is difficult. To resolve this issue, we attached a small photo multiplier tube (PMT) tightly to the body surface of transgenic mice carrying a reporter gene such that the photon input window faced target organs such as the liver and kidney and succeeded in long-term continuous measurement of circadian gene expression in semi-freely moving mice over periods of several weeks. Using this simple method, we clearly showed that lithium causes circadian period elongation in peripheral clock gene expression rhythms in vivo. Further development of our detection system to maturity will aid a wide range of research fields in medicine and biology.

Dual-energy high-count-rate X-ray computed tomography scanner using a cerium-doped yttrium aluminum perovskite crystal and a small-photomultiplier tube

To obtain two kinds of tomograms at two different X-ray energy ranges simultaneously, we have constructed a dual-energy X-ray photon counter with a high-count-rate detector system, three comparators, two microcomputers, and two frequency-voltage converters. The detector system consists of a cerium-doped yttrium aluminum perovskite [YAP(Ce)], a photomultiplier tube, an inverse amplifier, and a pulse-width extender. X-ray photons are detected using the detector system, and the event pulses are input to three comparators simultaneously to determine threshold energies. At a tube voltage of 100 kV, the three threshold energies are 35, 55 and 60 keV. X-ray photons in the two ranges are counted using microcomputers, and the logical pulses from the two microcomputers are input to two frequency-voltage converters. In dual-energy computed tomography (CT), the tube voltage and current were 100 kV and 0.25 mA, respectively. Two tomograms were obtained simultaneously at two energy ranges. The energy ranges for iodine and gadolinium K-edge CT were 35–60 and 55–100 keV, respectively. The maximum count rate of dual-energy CT was 85 kilocounts per second with energies ranging from 21 to 100 keV, and the exposure time for tomography was 9.8 min.

Design and production of the digital optical module of the KM3NeT project

The KM3NeT collaboration is building the ARCA and ORCA neutrino telescopes in the depths of the Mediterranean Sea. They will consist of 3-dimensional arrays of photodetectors, called digital optical modules, suspended in the sea by means of vertical string structures, called detection units. The optical modules are composed of a pressure-resistant 17-inch spherical glass vessel, which contains 31 small photomultiplier tubes and all the associated electronics. The multi- photomultiplier solution represents an innovative design with respect to optical modules of all currently operated neutrino telescopes comprising a single large photomultipliers.

A wearable sensor based on CLYC scintillators

We have developed a wearable radiation sensor using Cs2LiYCl6:Ce (CLYC) for simultaneous gamma-ray and neutron detection. The system includes two ∅2.5×2.5cm3 crystals coupled to small, metal-body photomultiplier tubes. A custom, low-power electronics base digitizes the output signal at three time points and enables both pulse height and pulse shape discrimination of gamma rays and neutrons. The total counts, anomaly detection metrics, and identified isotopes are displayed on a small screen. Users may leave the device in unattended mode to collect long-dwell energy spectra. The system stores up to 18h of one-second data, including energy spectra, and may transfer the data to a remote computer via a wired or wireless connection. The prototype is 18×13×7.5cm3, weighs 1.3kg, not including the protective pouch, and runs on six AA alkaline batteries for 29h with the wireless link active, or 41h with the wireless link disabled. In this paper, we summarize the system design and present characterization results from the detector modules. The energy resolution is about 6.5% full width at half maximum at 662keV due to the small photomultiplier tube selected, and the linearity and pulse shape discrimination performance are very good.

TRitium Activity Measurements with a PhotomultipliEr in Liquids–The TRAMPEL experiment

A common technique for the determination of the activity of tritiated water (HTO) is liquid scintillation counting (LSC). This implies sample taking, sample preparation and radioactive waste processing afterwards. When handling highly tritiated water special care has to be taken because of possible harmfulness of the sample. Furthermore, LSC devices are mostly large, heavy and expensive. The TRAMPEL experiment aims at measuring the activity of tritiated water in-line without sample taking. The device is intended to be easy to use and operate, quite inexpensive and compact. The measurement principle is based on electrons from β-decay which induce light in commercially available scintillation fibres. The light is detected by a small photomultiplier tube (PMT). A proof-of-principle was set up for static measurements using standard stainless steel parts. The complete device has a volume of less than 0.5 l.

WE-AB-BRB-03: Investigation of a Small Photomultiplier-Based Probe for Use in Beam Diagnostics and Medical Dosimetry

Purpose: Investigate the use of a small photomultiplier-based probe as a possible beam diagnostic and medical dosimetry tool. Methods: Cerenkov emission produced by clinical accelerator beams was detected by a small photomultiplier tube (PMT). Measurements of Clinac beams were made both in air and by inserting the PMT directly into a water phantom. A conical collimator placed in front of the PMT reduced the angular acceptance and the detection of scattered light. With this arrangement, we obtained response curves as a function of depth along the central axis similar in shape and magnitude to those obtained with ionization chambers. Subsequent measurements were made with the PMT covered in aluminum foil, obtaining a signal arising primarily from direct Cerenkov light produced in the glass entrance window. With an oscilloscope and amplifier/MCA system, we were able to monitor the response to individual beam pulses and observe variations in the beam pulse shape and magnitude as a function of dose rate. Results: Using Cerenkov signals detected by a PMT, we were able to obtain reasonable beam quality metrics, and the response was found to be linear over a range of dose rates. The fast response of the PMT allowed for the observation of small changes in the shape and magnitude of the beam pulse. With this system we were able to detect small changes in the dose per pulse delivered by the accelerator. Conclusion: A small PMT probe has shown promise as a beam diagnostic and medical dosimetry tool. Its fast response allows for real time beam pulse monitoring, and the integrated response can yield relative and perhaps even absolute dose information with a properly calibrated system. For accelerator diagnostics, monitoring of the beam pulse shape can aid in beam tuning, particularly in electron mode, where no target current pulse is available.

Zero-dark-counting high-speed X-ray photon detection using a cerium-doped yttrium aluminum perovskite crystal and a small photomultiplier tube and its application to gadolinium imaging

X-ray photons are detected using a cerium-doped yttrium aluminum perovskite [YAP(Ce)] single-crystal scintillator with a decay time of 30 ns and a small-sized photomultiplier tube (SPMT). The negative output pulse from the SPMT is amplified by a high-speed inverse amplifier, and the event pulses are sent to a multichannel analyzer to measure X-ray spectra. The energy resolution of the spectrometer was 15% at 59.5 keV. We carried out photon-counting computed tomography using gadolinium media with a maximum rate of 650 kilo counts per second and confirmed the energy-dispersive effect with changes in the description voltage of event pulses using a high-speed comparator.

A feasibility study for the detection of supernova explosions with an undersea neutrino telescope

We study the potential of a very large volume underwater Mediterranean neutrino telescope to observe neutrinos from supernova (SN) explosions within our galaxy. The intense neutrino burst emitted in a SN explosion results in a large number of MeV neutrinos inside the instrumented volume of the neutrino telescope that can be detected (mainly) via the reaction ν¯e+p⟶e++n. In this study we simulated the response of the underwater neutrino telescope to the electron antineutrino flux predicted by the Garching model for SN explosions. We assumed that the neutrino telescope comprises 6160 direction sensitive optical modules, each containing 31 small photomultiplier tubes. Multiple coincidences between the photomultiplier tubes of the same optical module are utilized to suppress the noise produced by 40K radioactive decays and to establish a statistical significant signature of the SN explosion.

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.

Development of scintillating crystal hybrid photon detectors for the KM3NeT ( [formula omitted]-scale) deep-sea neutrino telescope

Scintillating crystal-based hybrid photon detectors have been demonstrated as viable single photon detectors since 1996 in the Lake Baikal neutrino telescope. Prior to this, the Philips XP2600 was developed under the DUMAND program, while more recently, developments at CERN have demonstrated the advantages of a true concentric geometry with a scintillator at the geometric centre of a spherical photocathode, giving almost 100% electrostatic collection efficiency over 3 π solid angle coverage. We have started to develop a new series of quasi-spherical crystal hybrid photon detectors starting at 8 in. and progressing toward the maximum that can be fitting in a standard 17 in. optical pressure sphere for a future large deep-sea neutrino telescope. The thrust of this R&D will be to investigate the industrialisation of these sensors to the point where they represent a significant cost reduction per cubic kilometre of instrumented volume compared to conventional large hemispherical photomultiplier tubes, thereby allowing for extremely large telescope target volumes. Such gains will arise through an all-glass envelope, internal processing of a standard or enhanced bialkali photocathode, and either from cost reductions in the central scintillating crystal or the use of a deposited phosphor viewed by a small photomultiplier tube. Details of the development program and recent progress in the characterisation of prototypes are presented.

Sensitivity of a multi-photomultiplier optical module for KM3NeT

For the KM3NeT neutrino telescope an optical module with a number of small photomultiplier tubes (multi-PMT optical module) will be advantageous for various reasons, e.g. reduced background rate, a larger number of coincidence hits, and sensitivity to ultra-high energy neutrinos. The properties of such a design have been investigated by measurements and simulations. Several types of 3 in. PMT were exposed to LED light pulses with intensities down to the single-photon level. The simulation tool Sirène for a photo-sensor based neutrino telescope has been applied to allow a comparison with the ANTARES detector. All muon directions can be observed with an improved identification and rejection of atmospheric muons. For up-going neutrinos and down-going muons the multi-PMT arrangement shows a better performance in both the photo-electron response and in the number-of-hits response as compared to the present ANTARES design.

Multi-PMT optical module

In this paper we discuss the advantages of using many small photomultiplier tubes inside a cylindrical or spherical pressure vessel as an alternative to the “standard” large (10″) photomultiplier. The tube used for the test is the Photonis XP53x2 tube which has a diameter of 3″. We show that in terms of signal to noise the small phototube solution is superior to the large tube. Tests show that the small tubes can be successfully operated feeding 12 tubes from a single high voltage power supply, using individual high resistance bases. The readout using a time over threshold technique has also been investigated and shows very promising results.

Alternative techniques for beam halo measurements

In future high intensity, high energy accelerators, it must be ensured that particle losses are minimized, as activation of the vacuum chambers or other components makes maintenance and upgrade work time consuming and costly. It is imperative to have a clear understanding of the mechanisms that can lead to halo formation and to have the possibility to test available theoretical models with an adequate experimental set-up. Measurements based on optical transition radiation are a well-established technique for measurements of the transverse beam profile. However, in order to be suitable for halo measurements as well, the dynamic range of the final image acquisition system needs to be high, being able to cover at least five orders of magnitude in intensity changes. Here, the performance of a standard acquisition system as it is used in the CLIC test facility (CTF3) is compared to a step-by-step measurement with a small movable photo multiplier tube and an innovative camera system based on charge injection device (CID) technology. Special emphasis is given to a description of the characteristics of the latter system.

First beam test on a BSO electromagnetic calorimeter

A beam test has been performed on a prototype electromagnetic calorimeter of bismuth silicate BSO crystals for the first time using electrons of 0.5–3.0 GeV. The calorimeter consists of nine BSO crystals, 22 mm × 22 mm × 180 mm (15.6 radiation lengths), arranged in a 3 × 3 array. Each crystal is coupled to a small photomultiplier tube of 20 mm in diameter. The obtained energy resolution is σ E / E = ( 0.023 ± 0.003 ) / E ( GeV ) ⊕ ( 0.017 ± 0.002 ) for incident electrons of the energy E in GeV. The position information for an electron injected onto the center crystal of the calorimeter array is given with energy deposit signals from nine BSO crystals. The RMS position resolution σ x is parameterized as σ x = [ ( 3.2 ± 0.1 ) / E ( GeV ) ⊕ ( 1.3 ± 0.1 ) ] mm at the center of the crystal. Misidentification probability of pions to electrons is found to be ∼ 10 - 3 for the pion momentum ranging from 1.0 to 3.0 GeV/ c.

Avalanche photodiodes in scintillation detection

Abstract This paper summarizes our studies on performance of Large Area Avalanche Photodiodes (LAAPDs) in gamma rays scintillation detection. Produced by Advanced Photonix, Inc. LAAPDs, because of their high sensitivity, low excess noise and large active area can potentially replace small area photomultiplier tubes (PMTs) in readout of scintillators. Several inorganic scintillators have been used to evaluate performance of commercially available LAAPDs as light readout devices in gamma-ray spectroscopy and timing measurements. The main factors limiting energy resolution have been analyzed and the experimental results have been compared with those obtained with PMT readout. Notably better or comparable energy resolutions to those observed with a XP2020Q photomultiplier were obtained with the LAAPDs for a number of different scintillators. Particularly, the recorded energy resolutions of 4.3±0.2% and 4.8±0.14% measured with YAP and CsI(Tl) crystals, respectively, for the 662 keV γ - peak from a 137 Cs source belong to the best observed ever with these scintillators. Results of the study of timing with fast scintillators coupled to the LAAPDs showed subnanosecond time resolution of 570 ps for 60 Co γ -rays detected with LSO crystal.

Thin Beta-ray Detectors using Plastic Scintillator Combined with Wavelength-shifting Fibers for Surface Contamination Monitoring

A thin β-ray detector for surface contamination monitoring has been newly developed. This detector, which we call a “wavelength-shifting” β-ray detector, consists of a thin square plastic scintillator plus wavelength-shifting fibers (WLSFs) to collect scintillation photons. The WLSFs are attached to opposite edges of the scintillator, where they convert highly concentrated scintillation photons into fluorescence. The fluorescent photons can either be detected directly at the ends of the WLSFs or through transparent optical fibers by small photo-multiplier tubes (PMTs). This design provides a thin detector profile while offering good β-ray detection performance.We first carry out a theoretical evaluation of the light output of this design. Then we describe verification tests aimed at device evaluation, including some performance tests using trial-manufactured detectors. The results demonstrate that the new design offers good sensitivity and uniformity, and that the required detection limit for surface contamination monitoring is achieved. Finally, we confirm that the newly developed detectors are suitable for practical application.