Scintillation Photons Research Articles

The high-precision detector of the JUNO-TAO experiment

The Taishan Antineutrino Observatory (TAO) is a proposed ton scale liquid scintillator (LS) detector designed to precisely measure the reactor neutrino energy spectrum with the highest possible energy resolution. This will provide a reference spectrum for Jiangmen Underground Neutrino Observatory (JUNO) and a benchmark to verify the nuclear database. As a satellite experiment of JUNO, TAO will be installed near the reactor core at a distance of ∼30m. The detector uses 2.8m3 of Gd-doped liquid scintillator (∼1 ton fiducial volume, Gd-LS) contained in a spherical acrylic vessel. To maximize the photon collection efficiency in the detector, a 10m2 SiPM array is proposed to fully cover the acrylic vessel and collect as many scintillation photon as possible. The photon detection efficiency of SiPMs should be larger than 50%, in order to achieve the desired energy resolution (1.5%/E, photon statistical resolution). Additionally, the SiPMs will be operated at low temperature (−50 °C or lower) to reduce dark noise. Meanwhile, a shield and muon veto system will be located outside of the neutrino detector to control the environmental background. An overview of the JUNO-TAO experiment and its current progress are discussed.

(Invited) Photoluminescence and Scintillation Properties of Heavy Single Crystal Scintillators for X- and Gamma-Ray Detection

Scintillators are one of the luminescent materials, and have a function to convert a quantum of ionizing radiation to thousands of low energy photons immediately via interactions between the material and ionizing radiation [1,2]. Generally, scintillators are combined with photodetectors, and when the scintillation photons are emitted from the scintillator, photodetectors convert them to electrical signals. When the target ionizing radiation is high energy photons such as X- and gamma-rays, heavy materials are preferable for scintillators since the detection efficiency against high energy photons depends on density and effective atomic number. Up to now, many types of materials have been examined for scintillators, such as single crystals, glasses, and opaque and transparent ceramics [2]. Among them, bulk single crystalline scintillators have been applied for scintillation detectors owing to a superior optical quality including high transmittance and luminescence efficiency.In the conference, some recent results of development of heavy scintillators mainly containing Lu, Hf, Ta and Tl are introduced. These materials were synthesized by some single crystal growth techniques such as the floating zone and bridgman method. After the synthesis, they were examined on optical (photoluminescence excitation and emission spectra and decay curve) and scintillation (scintillation emission spectrum, decay curve, afterglow and pulse height) properties. In Lu-based crystals, rare earth doped Lu2O3 crystals are introduced, and especially, Tb- and Eu-doped ones show a high scintillation light yield. In Hf-based ones, some results of rare earth doped AEHfO3 (AE = alkali earth) crystals are presented, and Ce-doped (Mg,Ca)HfO3 shows a high scintillation light yield [3]. Among Ta-based crystals, Mg4(Nb,Ta)2O9 crystals have a high light yield due to charge transfer luminescence of Ta/Nb and O [4]. In Tl-based crystalline compounds, TlMgCl3 shows a high light yield and energy resolution [5]. In the conference, these results will be introduced.

Scintillation Properties of LaMgAl11O19:Er Crystals with NIR Luminescence

A scintillator is a phosphor that emits photons with several eV when irradiated by ionizing radiations and has been used in applications such as medical diagnostic, security, resource exploration etc. A scintillation detector consists of a scintillator that converts ionizing radiations into photons and a photodetector such as a photomultiplier tube or photodiode that converts photons into electrical signals. Since the conversion efficiency from photon to electrical signal depends on the quantum efficiency of the photodetector, phosphors that emit in the UV–visible region, where the above photodetectors have high sensitivity, have been investigated.Since the nuclear accident in Fukushima, various countermeasures using materials have been studied for reconstruction. In recent years, scintillators which exhibit luminescence in the near-infrared (NIR) region have attracted attention for remote monitoring applications in high-dose fields. Remote monitoring using scintillators and optical fibers has been proposed to avoid radiation damage to semiconductors and electrical circuits of signal amplifiers involved in measurements. Since the method uses a long optical fiber, the transmission efficiency of scintillation photons in an optical fiber is important. In the NIR region of 800–1700 nm, the transmittance of a quartz fiber is higher than that in the UV–visible region, and the transmission loss can be suppressed. So far, there have been sporadic studies on NIR-scintillators. In the past studies, only emission wavelengths shorter than 1000 nm were monitored because a Si-photodiode was used as the photodetector. On the other hand, InGaAs-based photodiodes enable stable measurement of NIR scintillation photons with wavelengths longer than 1000 nm. In our previous works, various scintillators doped with Nd as an emission center in the NIR region have been developed as candidate materials.LaMgAl11O19 has been extensively studied in various phosphor fields such as laser and white LED applications. Since LaMgAl11O19 has La3+ sites that can be easily substituted with doped rare-earth ions as an emission center, LaMgAl11O19 doped with various trivalent rare-earth ions such as Ce, Nd, Sm, Eu, Dy, Tm, Yb etc. has been investigated. In addition, compared with conventional oxide scintillators such as rare-earth-based silicate and aluminate compounds, the composition ratio of rare-earth elements is relatively low, and the main component is Al2O3, so the cost of raw materials can be suppressed. However, no research on the scintillation properties for measuring ionizing radiations has been reported so far. In this study, the rare-earth-doped LaMgAl11O19 single crystals were synthesized, and the photoluminescence and scintillation properties were investigated to evaluate the potential applicability for high-dose monitoring applications.

Monte Carlo calculations of cryogenic photodetector readout of scintillating GaAs for dark matter detection

The recent discovery that GaAs(Si,B) is a bright cryogenic scintillator with no apparent afterglow offers new opportunities for detecting rare, low-energy, electronic excitations from interacting dark matter. This paper presents Monte Carlo calculations of the scintillation photon detection efficiencies of optical cavities using three current cryogenic photodetector technologies. In order of photon detection efficiency these are: (1) Ge/TES: germanium absorbers that convert interacting photons to athermal phonons that are readout by transition edge sensors, (2) KID: kinetic induction detectors that respond to the breaking of cooper pairs by a change in resonance frequency, and (3) SNSPD: superconducting nanowire single photon detectors, where a photon briefly transitions a thin wire from superconducting to normal. The detection efficiencies depend strongly on the n-type GaAs absolute absorption coefficient KA, which is a part of the narrow beam absorption that has never been directly measured. However, the high cryogenic scintillation luminosity of GaAs(Si,B) sets an upper limit on KA of 0.03/cm. Using that value and properties published for Ge/TES, KID, and SNSPD photodetectors, this work calculates that those photodetectors attached to opposing faces of a 1 cm3 cubic GaAs(Si,B) crystal in an optical cavity with gold mirrors would have scintillation photon detection efficiencies of 35%, 25%, and 8%, respectively. Larger values would be expected for lower values of KA.

Predicting time-of-flight with Cerenkov light in BGO: a three-stage network approach with multiple timing kernels prior

Objective.In the quest for enhanced image quality in positron emission tomography (PET) reconstruction, the introduction of time-of-flight (TOF) constraints in TOF-PET reconstruction offers superior signal-to-noise ratio. By employing BGO detectors capable of simultaneously emitting prompt Cerenkov light and scintillation light, this approach combines the high time resolution of prompt photons with the high energy resolution of scintillation light, thereby presenting a promising avenue for acquiring more precise TOF information.Approach.In Stage One, we train a raw method capable of predicting TOF information based on coincidence waveform pairs. In Stage Two, the data is categorized into 25 classes based on signal rise time, and the pre-trained raw method is utilized to obtain TOF kernels for each of the 25 classes, thereby generating prior knowledge. Within Stage Three, our proposed deep learning (DL) module, combined with a bias fine-tuning module, utilizes the kernel prior to provide bias compensation values for the data, thereby refining the first-stage outputs and obtaining more accurate TOF predictions.Main results.The three-stage network built upon the LED method resulted in improvements of 11.7 ps and 41.8 ps for full width at half maximum (FWHM) and full width at tenth maximum (FWTM), respectively. Optimal performance was achieved with FWHM of 128.2 ps and FWTM of 286.6 ps when CNN and Transformer were utilized in Stages One and Three, respectively. Further enhancements of 2.3 ps and 3.5 ps for FWHM and FWTM were attained through data augmentation methods.Significance.This study employs neural networks to compensate for the timing delays in mixed (Cerenkov and scintillation photons) signals, combining multiple timing kernels as prior knowledge with DL models. This integration yields optimal predictive performance, offering a superior solution for TOF-PET research utilizing Cerenkov signals.

Novel Liquid Argon Time-Projection Chamber Readouts

Liquid argon time-projection chambers (LArTPCs) have become a prominent tool for experiments in particle physics. Recent years have yielded significant advances in the techniques used to capture the signals generated by these cryogenic detectors. This article summarizes these novel developments for detection of ionization electrons and scintillation photons in LArTPCs. New methods to capture ionization signals address the challenges of scaling traditional techniques to the large scales necessary for future experiments. Pixelated readouts improve signal fidelity and expand the applicability of LArTPCs to higher-rate environments. Methods that leverage amplification in argon enable measurements in the keV regime and below. Techniques to enhance collection of argon scintillation photons improve calorimetry and expand the physics program for very large detectors. Future efforts aim to demonstrate systems for the combined detection of both electrons and photons.

Investigation of scintillation properties of a CsI(Tl) crystal at low temperature for dark matter search

The Korea invisible mass search (KIMS) experiment used CsI(Tl) crystals coupled with photomultiplier tubes (PMTs) to detect signals from weakly interacting massive particles (WIMPs) at room temperature. It is expected that combining CsI(Tl) crystals with silicon photomultipliers (SiPMs) will enhance the detection performance. However, SiPMs must operate at low temperatures to reduce the dark count rate. In this study, we examined the temperature dependence of CsI(Tl) crystal properties, including light yield, α/β ratio, decay time, and pulse shape discrimination, before integrating it with a SiPM. The CsI(Tl) crystal was placed in a low-temperature chamber with a radiation source, and scintillation photons were detected by a PMT positioned outside the chamber. The response of CsI(Tl) to α-particles and γ-rays was examined across temperatures ranging from 10 K to 300 K.

Burn-in test and thermal performance evaluation of Silicon Photomultipliers for the JUNO-TAO experiment

This study evaluates more than 4,000 tiles made of Hamamatsu visual-sensitive silicon photomultipier (SiPM), each with dimensions of 5 × 5 cm2, intended for the central detector of the Taishan Anti-neutrino Observatory (TAO), a satellite experiment of the Jiangmen Underground Neutrino Observatory (JUNO) aimed at measuring the reactor anti-neutrino energy spectrum with unprecedented energy resolution. All SiPM tiles underwent a room temperature burn-in test in the dark for two weeks, while cryogenic testing analyzed the thermal dependence of parameters for some sampled SiPMs. Results from these comprehensive tests provide crucial insights into the long-term performance and stability of the 10 square meters of SiPMs operating at -50°C to detect scintillation photons in the TAO detector. Despite some anomalies awaiting further inspection, all SiPMs successfully passed the burn-in test over two weeks at room temperature, which is equivalent to 6.7 years at -50°C. Results are also used to guide optimal SiPM selection, configuration, and operation, ensuring reliability and sustainability in reactor neutrino measurements. This work also provides insights for a rapid and robust quality assessment in future experiments that employ large-scale SiPMs as detection systems.

Analysis of the S1 triplet component in the DarkSide-50 experiment

The DarkSide-50 (DS-50) experiment aims at the direct detection of weakly interacting massive particles. It is a dual-phase liquid argon time projection chamber (LAr TPC) where Dark Matter (DM), which constitutes five sixths of all matter in the universe, is expected to interact with an argon nucleus resulting in a nuclear recoil. A scintillation signal (S1) is produced as a result of the ionising events from the DM-Ar interaction. The impurities in LAr, such as O,2, N2, H2O, etc., at the ppm level, quench the scintillation photons, leading to a reduction in the observed lifetime of the triplet state. In this contribution, the effect of impurities on the triplet lifetime is analyzed for individual events using DS-50 data, with a primary focus on nitrogen, one of the candidates for the impurities in LAr hypothesized to cause a suppression of triplet lifetime. This is done by determining the lifetime of the triplet component with a known purity, which can be used as a reference for the purity level of argon used in current and future dark matter searches.

Expected performance of Cosmic Muon Veto Detector

The India-based Neutrino Observatory (INO) collaboration has established a miniICAL detector, at the transit campus of IICHEP, Madurai, India, which serves as a prototype detector of the larger Iron-Calorimeter detector (ICAL). The purpose of miniICAL lies in unraveling the intricate physics and engineering challenges inherent in constructing and operating a substantial ICAL-type detector. To explore the feasibility of building a large-scale neutrino experiment at shallow depths the collaboration has embarked upon the construction of a Cosmic Muon Veto Detector (CMVD) around the miniICAL detector. The primary objective of this endeavor revolves around attaining a veto efficiency surpassing 99.99%, while simultaneously maintaining a false-positive rate lower than 10-5. The CMVD system is based on extruded plastic scintillators (EPS) and utilizes wavelength-shifting fibers to collect scintillation photons and uses silicon photomultipliers (SiPMs) as photo-transducers. A software tool is developed for CMVD and is integrated with the existing miniICAL consisting of RPC detectors. The simulation is tuned to include properties of EPSs and WLS fibers, measured efficiencies, and time resolutions of EPSs. Measured spectra and noise in SiPMs are also taken into account. The muon tracks in the RPCs are used to estimate the muon veto efficiency of CMVD to arrive at efficient muon veto criteria. With improved veto efficiency of cosmic muons, the CMVD experiment will help to pave the way for future large-scale shallow-depth neutrino experiments e.g. INO-type experiments, enhancing our understanding of neutrino properties.

Electron density estimation using MPPC-based photon-counting CT for radiation therapy planning

Photon-counting computed tomography (PCCT) has been attracting attention recently, as a potential alternative to the conventional computed tomography (CT). With PCCT, the photon energy can be obtained, and the amount of exposure can be reduced compared with the conventional CT. We developed a detector system composed of a scintillator and multi-pixel photon counter (MPPC). This makes the system simple and inexpensive compared with the semiconductor-based PCCT, like CdTe and CZT. In this study, we propose estimating electron density for radiation therapy planning using a six-threshold MPPC-based photon-counting detector. Electron density is an essential information for determining beam energy in radiation therapy planning. Therefore, accurate electron density estimation is required. The estimation method used in this study is based on the method proposed by Saito et al. (2012) PCCT images of electron-density-known phantoms were acquired, and information of the two out of the six energy bands was used for estimation. As a result, we succeeded in estimating the electron density with an accuracy of 4.59% root-mean-square error. However, the lung phantoms, which had a relatively low electron density, still had a large deviation from the true value. In addition, dual-energy CT and PCCT estimation results were compared. PCCT results has not yet surpassed the accuracy of dual-energy CT (DECT) results; however, the high electron density materials were obtained almost at the same level of accuracy. In future, we will continue to work on more accurate electron density estimation using multiple energy band information.

Optimized α/β pulse shape discrimination in Borexino

Borexino could efficiently distinguish between α and β radiation in its liquid scintillator by the characteristic time profile of its scintillation pulse. This α/β discrimination, first demonstrated on the ton scale in the counting test facility prototype, was used throughout the lifetime of the experiment between 2007 and 2021. With this method, the α events are identified and subtracted from the solar neutrino events similar to β. This is particularly important in liquid scintillators, as the α scintillation is strongly quenched. In Borexino, the prominent Po210 decay peak was a background in the energy range of electrons scattered from Be7 solar neutrinos. Optimal α/β discrimination was achieved with a , with a higher ability to leverage the timing information of the scintillation photons detected by the photomultiplier tubes. An event-by-event, high efficiency, stable, and uniform pulse shape discrimination was essential in characterizing the spatial distribution of background in the detector. This benefited most Borexino measurements, including solar neutrinos in the pp chain and the first direct observation of the CNO cycle in the Sun. This paper presents key milestones in α/β discrimination in Borexino as a term of comparison for current and future large liquid scintillator detectors. Published by the American Physical Society 2024

Understanding the xenon primary scintillation yield for cutting-edge rare event experiments

Xenon scintillation has been widely used in rare event detection experiments, such as in neutrinoless double beta decay, double electron captures and dark matter searches. Nonetheless, experimental values for primary scintillation yield in gaseous xenon (GXe) remain scarce and dispersed. The mean energy required to produce a scintillation photon, w sc, in GXe in the absence of recombination has been measured to be in the range of 34–111 eV. Lower w sc-values were reported for α-particles when compared to electrons produced by γ- or x-rays. Since w sc is expected to be similar for x-, γ-rays or electrons and almost equal to that obtained for α-particles, the above difference can not be understood. In addition, at present one may also pose the question of a dependence of w sc on photon energy. We carried out a systematic study on the absolute primary scintillation yield in GXe under reduced electric fields in the 70–300 V cm-1 bar-1 range and near atmospheric pressure, 1.2 bar, supported by a robust geometrical efficiency simulation model. We were able to clear-out the above standing problems: w sc was determined for x/γ-rays in the 5.9–60 keV energy range as well as for α-particles in the 1.5–2.5 MeV range, and no significant dependency neither on radiation type nor on energy has been observed. Our experimental w sc-values agree well with both up-to-date simulations and literature data obtained for α-particles. The discrepancy between our results and the experimental values found in the literature for x/γ-rays is discussed in this work and attributed to unaddressed large systematic errors in those previous studies. These findings can be extrapolated to other gases, and have impact on experiments such as double beta decay, double electron capture and directional dark matter searches while also on potential future detection systems such as DUNE-Gas. Only assuming the VUV emission band as is the case of most of the literature values, a mean w sc-value of 38.7 ± 0.6 (sta.)+7.7 -7.2 (sys.) eV was obtained. If the UV-VIS emission band is to be considered, the average energy to produce a photon was determined to be w 2nd = 43.5 ± 0.7 (sta.)+8.7 -8.1 (sys.) eV and w 3rd = 483 ± 7 (sta.+110 -105 (sys.) eV, in the VUV and UV-VIS bands, respectively.

Performance of a first full-size WOM-based liquid scintillator detector cell as prototype for the SHiP Surrounding Background Tagger

As a prototype detector for the SHiP Surrounding Background Tagger (SBT), we constructed a cell (120 cm × 80 cm × 25 cm) made from corten steel that is filled with liquid scintillator (LS) composed of linear alkylbenzene (LAB) and 2,5-diphenyloxazole (PPO). The detector is equipped with two Wavelength-shifting Optical Modules (WOMs) for light collection of the primary scintillation photons. Each WOM consists of an acrylic tube that is dip-coated with a wavelength-shifting layer on its surface. Via internal total reflection, the secondary photons emitted by the molecules of the wavelength shifter are guided to a ring-shaped array of 40 silicon photomultipliers (SiPMs) coupled to the WOM for light detection. The granularity of these SiPM arrays provides an innovative method to gain spatial information on the particle crossing point. Several improvements in the detector design significantly increased the light yield with respect to earlier proof-of-principle detectors. We report on the performance of this prototype detector during an exposure to high-energy positrons at the DESY II test beam facility by measuring the collected integrated yield and the signal time-of-arrival in each of the SiPM arrays. The resulting detection efficiency and reconstructed energy deposition of the incident positrons are presented, as well as the spatial and time resolution of the detector. These results are then compared to Monte Carlo simulations.

Reactor neutrino physics potentials of cryogenic pure-CsI crystal

AbstractThis paper presents a world-leading scintillation light yield among inorganic crystals measured from a 0.5 kg pure-CsI detector operated at 77 Kelvin. Scintillation photons were detected by two 2-inch Hamamatsu SiPM arrays equipped with cryogenic front-end electronics. Benefiting the light yield enhancement of pure-CsI at low temperatures and the high photon detection efficiency of SiPM, a light yield of 30.1 photoelectrons per keV energy deposit was obtained for X-rays and $$\gamma $$ γ -rays with energies from 5.9 to 59.6 keV. Instrumental and physical effects in the light yield measurement are carefully analyzed. This is the first stable cryogenic operation of kg-scale pure-CsI crystal readout by SiPM arrays at liquid nitrogen temperatures for several days. The world-leading light yield opens a door for the usage of pure-CsI crystal in several fields, particularly in detecting the coherent elastic neutrino-nucleus scattering of reactor neutrinos. The potential of using pure-CsI crystals in neutrino physics is discussed in the paper.

Depth-encoding using optical photon TOF in a prism-PET detector with tapered crystals.

High-resolution brain positron emission tomography (PET) scanner is emerging as a significant and transformative non-invasive neuroimaging tool to advance neuroscience research as well as improve diagnosis and treatment in neurology and psychiatry. Time-of-flight (TOF) and depth-of-interaction (DOI) information provide markedly higher PET imaging performance by increasing image signal-to-noise ratio and mitigating spatial resolution degradation due to parallax error, respectively. PET detector modules that utilize light sharing can inherently carry DOI information from the multiple timestamps that are generated per gamma event. The difference between two timestamps that are triggered by scintillation photons traveling in opposite directions signifies the event's depth-dependent optical photon TOF (oTOF). However, light leak at the crystal-readout interface substantially degrades the resolution of this oTOF-based depthencoding. We demonstrate the feasibility of oTOF-based depth encoding by mitigating light leak in single-ended-readout Prism-PET detector modules using tapered crystals. Minimizing light leak also improved both energy-based DOI and coincidence timingresolutions. The tapered Prism-PET module consists of a 16 16 array of 1.5 1.5 20 lutetium yttrium oxyorthosillicate (LYSO) crystals, which are tapered down to 1.2 1.2 at the crystal-readout interface. The LYSO array couples 4-to-1 to an 8 8 array of 3 3 silicon photomultiplier (SiPM) pixels on the tapered end and to a segmented prismatoid light guide array on the opposite end. Performance of tapered and non-tapered Prism-PET detectors was experimentally characterized and evaluated by measuring flood histogram, energy resolution, energy-, and oTOF-based DOI resolutions, and coincidence timing resolution. Sensitivities of scanners using different Prism-PET detector designs were simulated using Geant4 application for tomographic emission (GATE). For the tapered (non-tapered) Prism-PET module, the measured full width at half maximum (FWHM) energy, timing, energy-based DOI, and oTOF-based DOI resolutions were 8.88 (11.18)%, 243 (286)ps, 2.35 (3.18)mm, and 5.42 (13.87)mm, respectively. The scanner sensitivities using non-tapered and tapered crystals, and 10 rings of detector modules, were simulated to be 30.9 and 29.5kcps/MBq,respectively. The tapered Prism-PET module with minimized light leak enabled the first experimental report of oTOF-based depth encoding at the detector module level. It also enabled the utilization of thinner (i.e., 0.1mm) inter-crystal spacing with barium sulfate as the reflector while also improving energy-based DOI and timingresolutions.

Evaluation of the capability of coumarin dye as a liquid scintillator for gamma ray detection and compton edge localization

In this work, we developed a highly sensitive liquid scintillator (LS) using Coumarin 450 (C450) dye to detect gamma ray and localize Compton edges (CEs). C450 exhibited absorption and fluorescence peaks at 350 nm and 407 nm, respectively, in toluene, at an optimized concentration (3 mM). The LS, contained in a standard glass container (1.8 cm diameter, 3.6 cm height), showed an emission peak in the blue region, matching the high quantum yield of typical PMT photocathodes. We exposed the LS to various gamma radiation sources (137Cs, 60Co, and 22Na), recording responses for different PMT voltages. Gaussian fitting of pulse height distribution spectrum allowed CE identification at the half-height for all PMT voltages. We compared theoretical and experimental results to a GEANT4-simulated detector, obtaining CE positions for radiation interactions and scintillation photon transport. The calibrated GEANT4 simulation was compared to experimental spectra to locate the Compton edges.

Capillary Manganese Halide Needle-Like Array Scintillator with Isolated Light Crosstalk for Micro-X-Ray Imaging.

The exacerbation of inherent light scattering with increasing scintillator thickness poses a major challenge for balancing the thickness-dependent spatial resolution and scintillation brightness in X-ray imaging scintillators. Herein, a thick pixelated needle-like array scintillator capable of micrometer resolution is fabricated via waveguide structure engineering. Specifically, this involves integrating a straightforward low-temperature melting process of manganese halide with an aluminum-clad capillary template. In this waveguide structure, the oriented scintillation photons propagate along the well-aligned scintillator and are confined within individual pixels by the aluminum reflective cladding, as substantiated from the comprehensive analysis including laser diffraction experiments. Consequently, thanks to isolated light-crosstalk channels and robust light output due to increased thickness, ultrahigh spatial resolutions of 60.8 and 51.7 lp mm-1 at a modulation transfer function (MTF) of 0.2 are achieved on 0.5mm and even 1mm thick scintillators, respectively, which both exceed the pore diameter of the capillary arrays' template (Φ = 10µm). As far as it is known, these micrometer resolutions are among the highest reported metal halide scintillators and are never demonstrated on such thick scintillators. Here an avenue is presented to the demand for thick scintillators in high-resolution X-ray imaging across diverse scientific and practical fields.

Scintillation and cherenkov photon counting detectors with analog silicon photomultipliers for TOF-PET

Objective. Standard signal processing approaches for scintillation detectors in positron emission tomography (PET) derive accurate estimates for 511 keV photon time of interaction and energy imparted to the detection media from aggregate characteristics of electronic pulse shapes. The ultimate realization of a scintillation detector for PET is one that provides a unique timestamp and position for each detected scintillation photon. Detectors with these capabilities enable advanced concepts for three-dimensional (3D) position and time of interaction estimation with methods that exploit the spatiotemporal arrival time kinetics of individual scintillation photons. Approach. In this work, we show that taking into consideration the temporal photon emission density of a scintillator, the channel density of an analog silicon photomultiplier (SiPM) array, and employing fast electronic readout with digital signal processing, a detector that counts and timestamps scintillation photons can be realized. To demonstrate this approach, a prototype detector was constructed, comprising multichannel electronic readout for a bismuth germanate (BGO) scintillator coupled to an SiPM array. Main Results. In proof-of-concept measurements with this detector, we were able to count and provide unique timestamps for 66% of all optical photons, where the remaining 34% (two-or-more-photon pulses) are also independently counted, but each photon bunch shares a common timestamp. We show this detector concept can implement 3D positioning of 511 keV photon interactions and thereby enable corrections for time of interaction estimators. The detector achieved 17.6% energy resolution at 511 keV and 237 ± 10 ps full-width-at-half-maximum coincidence time resolution (CTR) (fast spectral component) versus a reference detector. We outline the methodology, readout, and approach for achieving this detector capability in first-ever, proof-of-concept measurements for scintillation photon counting detector with analog silicon photomultipliers. Significance. The presented detector concept is a promising design for large area, high sensitivity TOF-PET detector modules that can implement advanced event positioning and time of interaction estimators, which could push state-of-the-art performance.

Characterization of external optical crosstalk reduction for SiPM-based scintillation detectors with an optical bandpass filter

External optical crosstalk remains a significant source of correlated noise in scintillation detectors optically coupled to silicon photomultiplier (SiPM) arrays and can influence achievable performance by limiting the maximum overvoltage at which a detector can be operated. This study evaluated the potential benefits of incorporating an optical bandpass filter, which is absorptive to optical crosstalk and transmissive for scintillation photons, between the scintillator and SiPM array. Several SiPM and bandpass configurations were characterized, including single-element and SiPM arrays with bare, filter-coupled, crystal-coupled, and crystal-filter-coupled interfaces. Coupling the optical filter between a 4 × 4 array of Broadcom AFBR-S4N44P164 M (NUV-MT) SiPMs and a 12 × 12 × 20 mm3 LYSO crystal decreased the total number of detected optical photon noise by up to 92%. The impact of the filter on crosstalk probability reduction was also characterized by the single-channel measurements with the same SiPM, suppressing external crosstalk up to 64%. With the filter coupled, SiPMs were operable at very high overvoltage. The results of these studies demonstrate that optical filtering is a promising technique to significantly reduce correlated noise in scintillation detectors employing SiPMs.