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Objective. Develop a prototype on-line positron emission tomography (PET) scanner and evaluate its capability of on-line imaging and intra-fractionated proton-induced radioactivity range measurement. Approach. Each detector consists of 32 × 32 array of 2 × 2 × 30 mm3 Lutetium–Yttrium Oxyorthosilicate scintillators with single-scintillator-end readout through a 20 × 20 array of 3 × 3 mm2 Silicon Photomultipliers. The PET can be configurated with a full-ring of 20 detectors for conventional PET imaging or a partial-ring of 18 detectors for on-line imaging and range measurement. All detector-level readout and processing electronics are attached to the backside of the system gantry and their output signals are transferred to a field-programable-gate-array based system electronics and data acquisition that can be placed 2 m away from the gantry. The PET imaging performance and radioactivity range measurement capability were evaluated by both the offline study that placed a radioactive source with known intensity and distribution within a phantom and the online study that irradiated a phantom with proton beams under different radiation and imaging conditions. Main results. The PET has 32 cm diameter and 6.5 cm axial length field-of-view (FOV), ∼2.3–5.0 mm spatial resolution within FOV, 3% sensitivity at the FOV center, 18%–30% energy resolution, and ∼9 ns coincidence time resolution. The offline study shows the PET can determine the shift of distal falloff edge position of a known radioactivity distribution with the accuracy of 0.3 ± 0.3 mm even without attenuation and scatter corrections, and online study shows the PET can measure the shift of proton-induced positron radioactive range with the accuracy of 0.6 ± 0.3 mm from the data acquired with a short-acquisition (60 s) and low-dose (5 MU) proton radiation to a human head phantom. Significance. This study demonstrated the capability of intra-fractionated PET imaging and radioactivity range measurement and will enable the investigation on the feasibility of intra-fractionated, range-shift compensated adaptive proton therapy. [ABSTRACT FROM AUTHOR]

Silicon photomultipliers (SiPMs) are solid-state single-photon-sensitive detectors that show excellent performance in a wide range of applications. In FBK (Trento, Italy), we developed a position-sensitive SiPM technology, called "linearly graded" (LG-SiPM), which is based on an avalanche-current weighted-partitioning approach. It shows position reconstruction resolution below 250 μm on an 8 × 8 mm2 device area with four readout channels and minimal distortions. A recent development in terms of LG-SIPM is a larger chip version (10 × 10 mm2) based on FBK NUV-HD technology (near-ultraviolet sensitive), with a peak photon detection efficiency at 420 nm. Such a large-area detector with position sensitivity is very interesting in applications like MR-compatible PET, high-energy physics experiments, and readout of time-projection chambers, gamma and beta cameras, or scintillating fibers, with a reduced number of channels. These SiPMs were characterized in terms of noise, photon detection efficiency, and position resolution. We also developed tiles of 2 × 2 and 3 × 3 LG-SiPMs, reaching very large sensitive areas of 20 × 20 mm2 and 30 × 30 mm2. We implemented a "smart-channel" configuration, which allowed us to have just six output channels for the 2 × 2 elements and eight channels for the 3 × 3 element tiles, preserving a position resolution below 0.5 mm. These kinds of detectors provide a great advantage in compact and low-power applications by maintaining position sensitivity over large areas with a small number of channels. [ABSTRACT FROM AUTHOR]

Background: Gamma camera imaging, including single photon emission computed tomography (SPECT), is crucial for research, diagnostics, and radionuclide therapy. Gamma cameras are predominantly based on arrays of photon multipliers tubes (PMTs) that read out NaI(Tl) scintillation crystals. In this way, standard gamma cameras can localize ɣ‐rays with energies typically ranging from 30 to 360 keV. In the last decade, there has been an increasing interest towards gamma imaging outside this conventional clinical energy range, for example, for theragnostic applications and preclinical multi‐isotope positron emission tomography (PET) and PET‐SPECT. However, standard gamma cameras are typically equipped with 9.5 mm thick NaI(Tl) crystals which can result in limited sensitivity for these higher energies. Purpose: Here we investigate to what extent thicker scintillators can improve the photopeak sensitivity for higher energy isotopes while attempting to maintain spatial resolution. Methods: Using Monte Carlo simulations, we analyzed multiple PMT‐based configurations of gamma detectors with monolithic NaI (Tl) crystals of 20 and 40 mm thickness. Optimized light guide thickness together with 2‐inch round, 3‐inch round, 60 × 60 mm2 square, and 76 × 76 mm2 square PMTs were tested. For each setup, we assessed photopeak sensitivity, energy resolution, spatial, and depth‐of‐interaction (DoI) resolution for conventional (140 keV) and high (511 keV) energy ɣ using a maximum‐likelihood algorithm. These metrics were compared to those of a "standard" 9.5 mm‐thick crystal detector with 3‐inch round PMTs. Results: Estimated photopeak sensitivities for 511 keV were 27% and 53% for 20 and 40 mm thick scintillators, which is respectively, 2.2 and 4.4 times higher than for 9.5 mm thickness. In most cases, energy resolution benefits from using square PMTs instead of round ones, regardless of their size. Lateral and DoI spatial resolution are best for smaller PMTs (2‐inch round and 60 × 60 mm2 square) which outperform the more cost‐effective larger PMT setups (3‐inch round and 76 × 76 mm2 square), while PMT layout and shape have negligible (< 10%) effect on resolution. Best spatial resolution was obtained with 60 × 60 mm2 PMTs; for 140 keV, lateral resolution was 3.5 mm irrespective of scintillator thickness, improving to 2.8 and 2.9 mm for 511 keV with 20 and 40 mm thick crystals, respectively. Using the 3‐inch round PMTs, lateral resolutions of 4.5 and 3.9 mm for 140 keV and of 3.5 and 3.7 mm for 511 keV were obtained with 20 and 40 mm thick crystals respectively, indicating a moderate performance degradation compared to the 3.5 and 2.9 mm resolution obtained by the standard detector for 140 and 511 keV. Additionally, DoI resolution for 511 keV was 7.0 and 5.6 mm with 20 and 40 mm crystals using 60 × 60 mm2 square PMTs, while with 3‐inch round PMTs 12.1 and 5.9 mm were obtained. Conclusion: Depending on PMT size and shape, the use of thicker scintillator crystals can substantially improve detector sensitivity at high gamma energies, while spatial resolution is slightly improved or mildly degraded compared to standard crystals. [ABSTRACT FROM AUTHOR]

This research investigates the fabrication and analysis of plastic scintillators using an epoxy matrix. Plastic scintillators are widely used in radiation detection because of their low cost, ease of fabrication, resistance to moisture, and rapid decay time. The production process involved dissolving primary and secondary dopants, p-terphenyl (p-TP) and 1,4-bis [2-(phenyloxazolyl)]-benzene (POPOP), respectively, into a low-viscosity of cycloaliphatic amine as hardener B, which was then combined with Bisphenol-A diglycidyl ether as epoxy A. The ratio of primary and secondary dopants was varied in the experiment. The resulting scintillators were characterized using Fourier Transform Infrared Spectroscopy (FTIR) to analyze the functional groups that constitute the epoxy before and after curing. The morphology of the scintillator sample was evaluated using SEM and The thermal properties were evaluated with differential scanning calorimetry (DSC). The optical properties of the scintillator were studied using a UV-Vis Spectrophotometer and a Fluorescence Spectrophotometer. The performance of the scintillator in detecting gamma rays was evaluated using a module comprising a Photomultiplier Tube (PMT) and a Multichannel Analyzer (MCA) with sources of gamma Cesium 137. The results showed that epoxy-based scintillators can provide a detective response to gamma rays. This study demonstrates the potential of epoxy-based plastic scintillators for use in radiation detection. [ABSTRACT FROM AUTHOR]

Background: 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 depth encoding. Purpose: 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 timing resolutions. Methods: The tapered Prism‐PET module consists of a 16 ×$\times$ 16 array of 1.5 ×$\times$ 1.5 ×$\times$ 20 mm3${\rm {mm}}^3$ lutetium yttrium oxyorthosillicate (LYSO) crystals, which are tapered down to 1.2 ×$\times$ 1.2 mm2${\rm {mm}}^2$ at the crystal‐readout interface. The LYSO array couples 4‐to‐1 to an 8 ×$\times$ 8 array of 3 ×$\times$ 3 mm2${\rm {mm}}^2$ 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). Results: 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 29.5 kcps/MBq, respectively. Conclusions: 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., 0.1 mm) inter‐crystal spacing with barium sulfate as the reflector while also improving energy‐based DOI and timing resolutions. [ABSTRACT FROM AUTHOR]

We explored the nonlinear characteristics of energy resolution (ER) for the sealed NaI (Tl) scintillator detector by using a gamma-ray spectroscopy system and Monte Carlo simulation. Our research focused on the two primary factors of energy resolution including the photomultiplier tube (PMT) voltage and the distance between the gamma-ray sources (137Cs and 60Co) and the scintillator detector. The experimental results showed that energy resolution decreased when the PMT voltage increased, and the energy resolution of NaI (Tl) detectors reached a smaller value (6.92%, 6.76%, and 6.56%), especially with the PMT voltage in the range of 575–595 V. In addition, a suitable distance between the gamma-ray source and the scintillator (5 cm) can also effectively reduce the energy resolution. We established the simulation models of the experimental NaI (Tl) detectors and simulated their energy spectra. The simulation results in the peak area agreed with the experimental results. A possible better PMT voltage choice has been proposed to obtain a smaller energy resolution. [ABSTRACT FROM AUTHOR]

The article describes a prototype device for monitoring the level of phase separation, which can be used for operational control of the delayed coking process in the petrochemical industry. A scheme and design of an experimental device developed by the authors, consisting of an organic plastic scintillator and an array of silicon photomultipliers, is presented. A computer simulation of the response of a scintillation detector under conditions of the actual geometry of the coke drum is presented. Experimental results demonstrating the performance of the device are presented. [ABSTRACT FROM AUTHOR]

Source localisation and real-time dose verification are at the forefront of medical research in brachytherapy, an oncological radiotherapy procedure based on radioactive sources implanted in the patient body. The ORIGIN project aims to respond to this medical community's need by targeting the development of a multi-point dose mapping system based on fibre sensors integrating a small volume of scintillating material into the tip and interfaced with silicon photomultipliers operated in counting mode. In this paper, a novel method for the selection of the optimal silicon photomultipliers to be used is presented, as well as a laboratory characterisation based on dosimetric figures of merit. More specifically, a technique exploiting the optical cross-talk to maintain the detector linearity in high-rate conditions is demonstrated. Lastly, it is shown that the ORIGIN system complies with the TG43-U1 protocol in high and low dose rate pre-clinical trials with actual brachytherapy sources, an essential requirement for assessing the proposed system as a dosimeter and comparing the performance of the system prototype against the ORIGIN project specifications. [ABSTRACT FROM AUTHOR]

Core to advancing time‐of‐flight positron emission tomography (ToF‐PET) toward a less invasive, more flexible procedure with a higher diagnostic power is the development of enhanced radiation detector materials. One promising avenue is the development of heterostructured scintillators where multiple materials work in synergy to exceed the performance of each individual component. Applied to ToF‐PET detectors, one component contributes predominantly to the absorption of gamma rays and the other to the creation of ultra‐fast photons. Whilst other authors have proposed various concepts, heterostructured scintillators are still in their infancy and scientifically guiding their development remains a challenge. Toward this aim and based on simulation and modeling developments, heterostructure properties are directly linked to ToF‐PET performance. This is made possible by redefining the notions of detector photo‐peak efficiency and timing response, as defined for monolithic detectors, in the context of heterostructured scintillators. Their overall potential is then discussed as a function of the materials and design used. This provides a quantitative framework to rapidly and efficiently support the advancement of heterostructured detectors for ToF‐PET technology. [ABSTRACT FROM AUTHOR]

In this paper, the details of the development and performance characterisation of a compact, low-power gamma spectrometer for environmental gamma radiation monitoring networks are presented. To reduce the power consumption and the size of the spectrometer, a gamma detector comprising a silicon photomultiplier coupled to a Gd3Ga3Al2O12:Ce,B (GGAG:Ce,B) scintillator has been used for gamma spectrometry. Initially, a Monte Carlo simulation study was carried out to verify the suitability of the 5 mm × 5 mm × 5 mm GGAG:Ce,B crystal for spectrometry of gamma sources in the energy range 60–1332 keV. For minimising the power consumption, the signal processing electronics has been custom designed. This electronics was realised using standard off-the-shelf components to reduce the cost. The developed spectrometer is of size 16 cm × 10 cm × 6 cm, weighs 600 g and consumes 600 mW power. The spectrometer is developed such that it could be directly interfaced with GSM/Xbee for wireless communication with the radiation monitoring networks. The lower-level discriminator threshold of the system is 40 keV and the total electronic noise is <20 keV. The experimentally measured sensitivity of the spectrometer for 137Cs (662 keV) is 2.4 cps/μGy/h at 3.5 V overvoltage. The spectrometer offers excellent linearity over the measured energy range of 60–1332 keV and an energy resolution of ~10% for 662 keV gamma-ray at room temperature. [ABSTRACT FROM AUTHOR]

Liquid scintillators are extensively employed as targets in neutrino experiments and in medical radiography. Perovskite nanocrystals are recognized for their tunable emission spectra and high photoluminescence quantum yields. In this study, we investigated the feasibility of using perovskites as an alternative to fluor, a substance that shifts the wavelengths. The liquid scintillator candidates were synthesized by doping perovskite nanocrystals with emission wavelengths of 450, 480, and 510 nm into fluor PPO with varying nanocrystal concentrations in a toluene solvent. The several properties of the perovskite nanocrystal-doped liquid scintillator were measured and compared with those of a secondary wavelength shifter, bis-MSB. The emission spectra of the perovskite nanocrystal-doped liquid scintillator exhibited a distinct monochromatic wavelength, indicating energy transfer from PPO to the perovskite nanocrystals. Using a 60 Co radioactive source setup with two photomultiplier tubes (PMTs), the light yields, pulse shape, and wavelength shifts of the scintillation events were measured. The light yields were evaluated based on the observed Compton edges from γ -rays, and compared across the synthesized samples. A decrease (or increase) in area-normalized PMT pulse height was observed at higher perovskite nanocrystal (or PPO) concentrations. The results demonstrated the sufficient potential of perovskite nanocrystals as an alternative to traditional wavelength shifters in a liquid scintillator. [ABSTRACT FROM AUTHOR]

Alpha particle detection performances of a Hamamatsu R1828-01 model and a RCA 6342A model photomultiplier tubes (PMT) were tested. For the sensitivity of the PMTs to alpha particles, an Eljen AJ-440 model ZnS(Ag) scintillator material in sheet form was used in front of their windows. To test their performances, the alpha peaks of an 241Am source and the energy resolution values of the detectors that composed of these PMTs were compared. It has been showed that R1828-01 model PMT utilized for fast timing measurements in radiation detection could be used in alpha particle detection efficiently. This work revealed its another advantageous feature in addition to existing specifications. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the performance of an electromagnetic (EM)‐tracked scintillation dosimeter in detecting source positional errors of IVD in HDR brachytherapy treatment. Materials and Methods: Two different scintillator dosimeter prototypes were coupled to 5 degrees‐of‐freedom (DOF) EM sensors read by an Aurora V3 system. The scintillators used were a 0.3 × 0.4 × 0.4 mm3 ZnSe:O and a BCF‐60 plastic scintillator of 0.5 mm diameter and 2.0 mm in length (Saint‐Gobain Crystals). The sensors were placed at the dosimeter's tip at 20.0 mm from the scintillator. The EM sampling rate was 40/s while the scintillator signal was sampled at 100 000/s using two photomultiplier tubes from Hamamatsu (series H10722) connected to a data acquisition board. A high‐pass filter and a low‐pass filter were used to separate the light signal into two different channels. All measurements were performed with an afterloader unit (Flexitron‐Elekta AB, Sweden) in full‐scattered (TG43) conditions. EM tracking was further used to provide distance/angle‐dependent energy correction for the ZnSe:O inorganic scintillator. For the error detection part, lateral shifts of 0.5 to 3 mm were induced by moving the source away from its planned position. Indexer length (longitudinal) errors between 0.5 to 10 mm were also introduced. The measured dose rate difference was converted to a shift distance, with and without using the positional information from the EM sensor. Results: The inorganic scintillator had both a signal‐to‐noise‐ratio (SNR) and signal‐to‐background‐ratio (SBR) close to 70 times higher than those of the plastic scintillator. The mean absolute difference from the dose measurement to the dose calculated with TG‐43U1 was 1.5% ±0.7%. The mean absolute error for BCF‐60 detector was 1.7% ±1.2%$\pm 1.2\%$ when compared to TG‐43 calculations formalism. With the inorganic scintillator and EM tracking, a maximum area under the curve (AUC) gain of 24.0% was obtained for a 0.5‐mm lateral shift when using the EMT data with the ZnSe:O. Lower AUC gains were obtained for a 3‐mm lateral shifts with both scintillators. For the plastic scintillator, the highest gain from using EM tracking information occurred for a 0.5‐mm lateral shift at 20 mm from the source. The maximal gain (17.4%) for longitudinal errors was found at the smallest shifts (0.5 mm). Conclusions: This work demonstrates that integrating EM tracking to in vivo scintillation dosimeters enables the detection of smaller shifts, by decreasing the dosimeter positioning uncertainty. It also serves to perform position‐dependent energy correction for the inorganic scintillator,providing better SNR and SBR, allowing detection of errors at greater distances from the source. [ABSTRACT FROM AUTHOR]

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Background: Positron emission tomography (PET) requires a high signal-to-noise ratio (SNR) to improve image quality, with time-of-flight (TOF) being an effective way to boost the SNR. However, the scanner sensitivity and resolution must be maintained. The use of axially aligned 100-mm LYSO:Ce,Ca scintillation crystals with double-sided readout has the potential of ground-breaking TOF and sensitivity, while reducing parallax errors through depth-of-interaction (DOI) estimation, and also allowing a reduction in the number of readout channels required, resulting in cost benefits. Due to orientation, these fibres may also facilitate the integration of TOF-PET with magnetic resonance imaging (MRI) in hybrid imaging systems. The challenge of achieving a good spatial resolution with such long axial fibres is directly related to the achievable TOF resolution. In this study, the timing performance and DOI resolution of emerging high-performance materials were investigated to assess the merits of this approach in organ-dedicated or total-body/large-scale PET imaging systems. Methods: LYSO:Ce,Ca scintillation fibres of 20 mm and 100 mm length were tested in various operating and readout configurations to determine the best achievable coincidence time resolution (CTR) and DOI resolution. The tests were performed using state-of-the-art high-frequency (HF) readout and commercially available silicon photomultipliers (SiPMs) from Broadcom Inc. Results: For the 100-mm fibre, an average CTR performance of 137 ± 1 ps FWHM and an average depth-of-interaction resolution within the fibre of 12.3 ± 0.5 mm FWHM could be obtained. The 20-mm fibre showed a sub-100 ps CTR of 98 ± 1 ps FWHM and a fibre resolution of 8.5 ± 0.2 mm FWHM in the double-sided readout configuration. Conclusion: With modern SiPMs and crystals, a double-sided readout of long fibres can achieve excellent timing resolution and field-advancing TOF resolution, outperforming commercial PET systems. With 100-mm fibres, an electronic channel reduction of about a factor 2.5 is inherent, with larger reduction factors conceivable, which can lead to lower production costs. The spatial resolution was shown to be limited in the axial direction with 12 mm, but is defined to 3 mm in all other directions. Recent SiPM and scintillator developments are expected to improve on the time and spatial resolution to be investigated in future prototypes. [ABSTRACT FROM AUTHOR]

Experiments with antiprotons often require the tracking of charged particles emerging from the annihilation process. The Atomic Spectroscopy And Collisions Using Slow Antiprotons (ASACUSA) collaboration at the CERN Antiproton Decelerator (AD) used several panels of scintillating bars placed around the interaction region to detect the passage of charged pions and determine the annihilation vertex position and time. The panels were composed by extruded scintillating bars and the light was collected using WaveLength Shifting (WLS) fibers and multi-anode PhotoMultiplier Tubes (PMTs). After operating for several years, the fiber-PMT coupling quality had degraded and a major upgrade of the light readout system was planned. The PMTs will be replaced by Silicon PhotoMultipliers (SiPMs) and the front-end electronics changed accordingly. An improvement is expected in the efficiency and the uniformity of the detector response. In this contribution the commissioning of the upgrade will be described, including the results of preliminary tests with cosmic rays. [ABSTRACT FROM AUTHOR]

Background: Fiber optic dosimetry (FOD) has emerged as a useful technique that can be used in those cases when intracavitary, real time, high spatial resolution dose assessment is required. Among the several factors characterizing a dosimeter, angular response of FOD probes has to be assessed in order to consider possible clinical application. Purpose: The objective of this study was to characterize the angular response of a FOD probe based on a cylindrical shaped YVO4:Eu3+ scintillator under irradiation with a 6 MV photon beam generated by a linear accelerator (LINAC). Methods: A FOD probe was irradiated inside a plastic phantom using a 6 MV LINAC photon beam at different azimuthal angles (0° to 360°, 15° steps). Scintillation output was measured with a photomultiplier tube. Similar measurements were performed with a second FOD probe having an optical filter interposed between the scintillator and the fiber. Monte Carlo simulations using PENELOPE were carried out in order to interpret the observed results. Results: The FOD output was symmetrical with respect to the scintillator axis. For the unfiltered probe, the signal was maximum at rear incidence (0°) and steadily decreased down to its minimum value at frontal incidence (180°) having a signal ratio of 37%. The output of the filtered probe showed a plateau from 15° up to 115°. The signal was maximum at 60° and minimum at 180° having a signal ratio of 16%. Monte Carlo simulations predicted symmetry of the deposited dose about 0° and 90°, which contrasts with experimental findings. Conclusions: Photoluminescence (PL) of the scintillator induced by the Cherenkov light increases the angular dependence. Radiation attenuation inside the scintillator and partial light collection of the scintillation yield by the optical fiber (OF) are responsible for asymmetrical response. Results from this study should be considered in order to minimize angular dependence in FOD. [ABSTRACT FROM AUTHOR]

Background: Fiber optic dosimetry (FOD) has emerged as a useful technique that can be used in those cases when intracavitary, real time, high spatial resolution dose assessment is required. Among the several factors characterizing a dosimeter, angular response of FOD probes has to be assessed in order to consider possible clinical application. Purpose: The objective of this study was to characterize the angular response of a FOD probe based on a cylindrical shaped YVO4:Eu3+ scintillator under irradiation with a 6 MV photon beam generated by a linear accelerator (LINAC). Methods: A FOD probe was irradiated inside a plastic phantom using a 6 MV LINAC photon beam at different azimuthal angles (0° to 360°, 15° steps). Scintillation output was measured with a photomultiplier tube. Similar measurements were performed with a second FOD probe having an optical filter interposed between the scintillator and the fiber. Monte Carlo simulations using PENELOPE were carried out in order to interpret the observed results. Results: The FOD output was symmetrical with respect to the scintillator axis. For the unfiltered probe, the signal was maximum at rear incidence (0°) and steadily decreased down to its minimum value at frontal incidence (180°) having a signal ratio of 37%. The output of the filtered probe showed a plateau from 15° up to 115°. The signal was maximum at 60° and minimum at 180° having a signal ratio of 16%. Monte Carlo simulations predicted symmetry of the deposited dose about 0° and 90°, which contrasts with experimental findings. Conclusions: Photoluminescence (PL) of the scintillator induced by the Cherenkov light increases the angular dependence. Radiation attenuation inside the scintillator and partial light collection of the scintillation yield by the optical fiber (OF) are responsible for asymmetrical response. Results from this study should be considered in order to minimize angular dependence in FOD. [ABSTRACT FROM AUTHOR]

Herein, details on the effect of Ce3+ concentration and annealing temperature on luminescence and scintillation properties of Y3Al5O12:Ce3+ (YAG:Ce3+) nanoscintillator powders, prepared by sol–gel method, have been investigated. Despite extensive research on YAG:Ce3+ single crystal, the behavior of this material at the nanoscale is still not fully understood. The photoluminescence spectra of nanoscintillator powders have been measured and analyzed. To properly assess the scintillation properties, the nanoscintillator sample powders are developed for use as a radiation detector and underwent preparation procedures, including surface homogenization and efficient coupling with a photomultiplier tube window. It is shown that even with nanoscintillator powders, pulse height spectra, with well‐resolved photo‐peak from the Compton edge, and scintillation decay curves are obtained. It is found that 0.5 mol% Ce3+ sample annealed at 1000 °C presents the nonradiative quenching concentration with calculated critical distance of 20.21 Å based on the resonance transfer by electric multipole–multipole interaction. Additionally, the sample detector with 0.5 mol% Ce3+ annealed at 1150 °C exhibits the highest light yield (LY) with value 18 900 ph MeV−1 and a better energy resolution value 10% full‐width and half‐maximum under 662 keV γ‐ray from 137Cs source. [ABSTRACT FROM AUTHOR]

Xenon is a widely used detector target material due to its excellent scintillation properties in the ultraviolet (UV) spectrum. The additional use of infrared (IR) scintillation light could improve future detectors. However, a comprehensive characterization of the IR component is necessary to explore its potential. We report on the first measurement of the time profile of the IR scintillation response of gaseous xenon. Our setup consists of a gaseous xenon target irradiated by an alpha particle source and is instrumented with one IR- and two UV-sensitive photomultiplier tubes. Thereby, it enables IR timing measurements with nanosecond resolution and simultaneous measurement of UV and IR signals. We find that the IR light yield is in the same order of magnitude as the UV yield. We observe that the IR pulses can be described by a fast and a slow component and demonstrate that the size of the slow component decreases with increasing levels of impurities in the gas. Moreover, we study the IR emission as a function of pressure. These findings confirm earlier observations and advance our understanding of the IR scintillation response of gaseous xenon, which could have implications for the development of novel xenon-based detectors. [ABSTRACT FROM AUTHOR]

Digital spectroscopy with Silicon Photomultiplier (SiPM) array coupled on CsI(Tl) crystal, needs some consideration to achieve desirable energy resolution. an array of SiPMs must be used with large scintillation crystal, therewithal signal from whole SiPMs is not ideal. Also silicon pixels are arranged in arrays at regular intervals. The distances between the pixels and the interference of the cross-talk of adjacent pixels are undesirable factors for energy resolution when the light is received by the crystal and transmitted to the SiPM array. On the other hand, due to the advantages of the SiPM array, there is a need to improve the energy resolution in order to be able to be applied. In this paper, an attempt is made to obtain the desired energy resolution by using the digital spectroscopy method and digital filters and properly shaping the output pulse of the preamplifier by the trapezoidal filter method. In this case, it will be possible to use it in different applications such as spectroscopy by the detector. [ABSTRACT FROM AUTHOR]

In positron emission tomography (PET), parallax errors degrade spatial resolution. The depth of interaction (DOI) information provides the position in the depth of the scintillator interacting with the γ-rays, thus reducing parallax errors. A previous study developed a Peak-to-Charge discrimination (PQD), which can separate spontaneous alpha decay in LaBr3:Ce. Since decay constant of GSO:Ce depends on Ce concentration, the PQD is expected to discriminate GSO:Ce scintillators with different Ce concentration. In this study, the PQD-based DOI detector system was developed, which can be processed online and implemented in PET. A detector was composed of four layers of GSO:Ce crystals and a PS-PMT. The four crystals were obtained from both the top and bottom of ingots with a nominal Ce concentration of 0.5 mol% and 1.5 mol%. The PQD was implemented on the Xilinx Zynq-7000 SoC board with 8ch Flash ADC to gain real-time processing, flexibility, and expandability. The results showed that the mean Figure of Merits in 1D between four scintillators are 1.5, 0.99, 0.91 for layers between 1st–2nd, 2nd–3rd, and 3rd–4th respectively, and the mean Error Rate in 1D between four scintillators are 3.50%, 2.96%, 13.3%, and 1.88% for layers 1, 2, 3, and 4, respectively. In addition, the introduction of the 2D PQDs resulted in the mean Figure of Merits in 2D greater than 0.9 and the mean Error Rate in 2D less than 3% in all layers. [ABSTRACT FROM AUTHOR]

The linear response of a photomultiplier tube (PMT) is a required property for photon counting and reconstruction of the neutrino energy. The linearity valid region and the saturation response of a PMT were investigated using a linear-alkylbenzene (LAB)-based liquid scintillator. A correlation was observed between the two different saturation responses, with pulse-shape distortion and pulse-area decrease. The observed pulse shape provides useful information for the estimation of the linearity region relative to the pulse area. This correlation-based diagnosis allows an in situ estimation of the linearity range, which was previously challenging. The measured correlation between the two saturation responses was employed to train an artificial neural network (ANN) to predict the decrease in pulse area from the observed pulse shape. The ANN-predicted pulse-area decrease enables a prediction of the ideal number of photoelectrons regardless of the saturation behavior. This pulse-shape-based machine-learning technique offers a novel method for restoring the saturation response of PMTs. [ABSTRACT FROM AUTHOR]

Objective. Together with novel photodetector technologies and emerging electronic front-end designs, scintillator material research is one of the key aspects to obtain ultra-fast timing in time-of-flight positron emission tomography (TOF-PET). In the late 1990s, Cerium-doped lutetium–yttrium oxyorthosilicate (LYSO:Ce) has been established as the state-of-the-art PET scintillator due to its fast decay time, high light yield and high stopping power. It has been shown that co-doping with divalent ions, such as Ca 2+ and Mg 2+, is beneficial for its scintillation characteristics and timing performance. Therefore, this work aims to identify a fast scintillation material to combine it with novel photosensor technologies to push the state of the art in TOF-PET. Approach. This study evaluates commercially available LYSO:Ce,Ca and LYSO:Ce,Mg samples manufactured by Taiwan Applied Crystal Co., LTD regarding their rise and decay times as well as their coincidence time resolution (CTR) with both ultra-fast high-frequency (HF) readout and commercially available readout electronics, i.e. the TOFPET2 ASIC. Main results. The co-doped samples exhibit state-of-the-art rise times of on average 60 ps and effective decay times of on average 35 ns. Using the latest technological improvements made on NUV-MT SiPMs by Fondazione Bruno Kessler and Broadcom Inc., a 3 × 3 × 19 mm3 LYSO:Ce,Ca crystal achieves a CTR of 95 ps (FWHM) with ultra-fast HF readout and 157 ps (FWHM) with the system-applicable TOFPET2 ASIC. Evaluating the timing limits of the scintillation material, we even show a CTR of 56 ps (FWHM) for small 2 × 2 × 3 mm3 pixels. A complete overview of the timing performance obtained with different coatings (Teflon, BaSO4) and different crystal sizes coupled to standard Broadcom AFBR-S4N33C013 SiPMs will be presented and discussed. Significance. This work thoroughly evaluates commercially available co-doped LYSO:Ce crystals and, in combination with novel NUV-MT SiPMs, shows a TOF performance that significantly exceeds the current state of the art. [ABSTRACT FROM AUTHOR]

A Hamamatsu R1828-01 model fast photomultiplier tube, i.e. having fast time response, was tested whether it can be utilized for the detection of alpha particles. An Eljen AJ-440 model ZnS(Ag) scintillator sheet was mounted on the front window of the PMT. In order to obtain best alpha detection performance, three different main amplifier models that are in our laboratory were used. The alpha energy resolution values were calculated through the amplifiers. Thus, the most appropriate amplifier model in the used ones was determined. It was shown that a fast PMT could be used in alpha particle detection in addition to the timing measurement. With this study, a Hamamatsu R18128-01 type PMT was first tested for the alpha detection and the detection performances through the main amplifiers were compared. [ABSTRACT FROM AUTHOR]

Recent progress in the field of scintillators and silicon photomultipliers (SiPM) has allowed development of new scintillation detectors capable of detecting low-energy X- and gamma-ray sources that are widely used in medicine, security and industry. Such scintillation detectors are compact, insensitive to magnetic fields, have low operation voltages and are functional at room temperature. These advantages of SiPM are considered to solve the main problems facing scintillation detectors in medicine and industry today. Development of detectors of low-energy electromagnetic radiation is relevant now. Scintillation detectors based on lutetium fine silicate, LaBr3(Ce), NaI and silicon avalanche photomultipliers offer a great potential for use for X- and gamma-ray detection. The present work demonstrates the gamma-ray detection performance of a new micropixel avalanche photodiode (MAPD) array (16 (4×4) elements - 15×15 cm) with a LaBr3(Ce) scintillator (15×15×30 mm) using 177Lu and 133Ba isotopes as the gamma-ray sources. [ABSTRACT FROM AUTHOR]

We investigated the correlation between the surface finish and luminescence properties of chemically polished cerium-doped single-crystal Gd3Al2Ga3O12 scintillators (Ce:GAGG), from the crystallographic perspective. The intrinsic defects in the crystals were identified via photoluminescence spectroscopy followed by scanning electron microscopy and X-ray diffraction to analyze their surface morphologies. Finally, the samples were individually wrapped with an enhanced specular reflector (ESR), coupled with a photomultiplier tube, placed inside a dark box, connected to a digitizer, and irradiated with a 137Cs radioactive source to evaluate the relative light (signal) output and energy resolution of each sample. The as-cut (rough) Ce:GAGG single-crystal samples, that were chemically polished with phosphoric acid at 190°C in air for 60 min, demonstrated a 33.1% increase in signal amplitude (light output to photosensor) and 2.4% (absolute value) improvement in energy resolution, which were comparable to those obtained for the mechanically polished sample. For these samples, the surface roughness was found to be ~430 nm, which was approximately half of that of the mechanically polished sample. The chemical polishing method used in this study is a cost-effective and straightforward technique to improve structural imperfections and can facilitate the treatment of inorganic scintillators with complex shapes and/or on a large scale. [ABSTRACT FROM AUTHOR]

A neutron detector with a micro-structured boron cathode and a glass gas electron multiplier (GEM) has been developed for time-of-flight Bragg edge neutron transmission imaging. The detector has a field of view of 100 x 100 mm² and 128 x 128 pixels (pixel size 0.8 x 0.8 mm²). The neutron imaging performance of the detector was evaluated at a compact electron accelerator-driven neutron source (AISTANS). By comparison with a Li-glass detector, we found that our detector has a detection efficiency of 5% for 4 Å neutrons. In addition, a preliminary time-of-flight neutron imaging test was performed to observe the difference between the face-centered and body-centered cubic crystal structures, from which we confirmed that our detector has sufficient stability and time resolution for use in Bragg edge imaging analysis. [ABSTRACT FROM AUTHOR]

We investigated the scintillation light yields of Tb-doped SiO2 glasses. We prepared 0.05, 0.1, and 0.5% Tb-doped SiO2 glasses by melting and solidifying sintered ceramic rods using an oxygen burner. The obtained samples showed no crystalline phases in X-ray diffraction measurements. Pulse height spectra of the Tb-doped SiO2 samples were measured under γ-ray excitation using a measurement system for slow decay pulses. The number of channels at the Compton edge of the 0.5% Tb-doped sample was the highest and was approximately 50% of that of a commercial lithium glass scintillator (GS20). By considering the light yield of GS20 and the wavelength dependence of the quantum efficiency of the photomultiplier tube, the light yield of the 0.5% Tb-doped SiO2 sample was estimated as 3800 photons/MeV. [ABSTRACT FROM AUTHOR]

High-resolution photon-counting detector (PCD) computed tomography (CT) imaging is increasingly used for several applications. Recent technological advances in CT instrumentation have introduced various types of radiation detectors. Therefore, this work aims at evaluating the lutetium–yttrium oxyorthosilicate (LYSO) scintillator for use in PCD CT from a detector point of view. To do so, a mini-CT prototype was designed and constructed based on the pixelated LYSO blocks. The detector comprises four 10 × 10 linearly arranged LYSO blocks coupled with four position-sensitive photomultiplier tubes. The prototype utilizes a point gamma-ray source along with a cone-beam collimator. An in-home MATLAB-based data processing software package was also developed for storing the list-mode data, event positioning, and energy windowing. A set of experiments were conducted to assess the performance of the constructed energy-resolved LYSO:Ce detector for mini-CT imaging. The results show good crystal identification for all blocks with a maximum peak-to-valley ratio of 3.48. In addition, the findings confirm that the developed detector is position-sensitive. The 20% energy window provides an optimal performance by simultaneously providing good crystal identification and a scatter removal factor of 0.71. A 96% uniformity was also observed when the detector was irradiated with a uniform flood. The spatial resolution of the mini-CT prototype in the x- and y-directions was calculated to be 0.9 and 0.93 mm, respectively, corrected for a magnification factor of 2.5. It is concluded that the pixelated LYSO crystal is a promising alternative to the current detectors and would be the scintillator of choice for high-resolution PCD CT imaging tasks. [ABSTRACT FROM AUTHOR]

The anti-Compton phoswich (ACP) detector, which is composed of multiple scintillators with one photomultiplier tube, takes into account the Compton suppression function and portability, and therefore, a discussion on how to design its shape to improve the performance of the detector has become necessary. Based on an ACP detector using a well-typed LaBr3:Ce/NaI:Tl composite scintillator that has been developed in the laboratory in early work, this study uses GEANT4 to simulate and study the influence of the change in the shape and size of the secondary scintillator on the performance of the detector, such as the Compton suppression ratio, the energy resolution, and the full-energy peak (FEP) loss. In the course of the study, we mainly investigate the variation of the performance of the detector in two ways. First, the inclination angle of the truncated cone is gradually changed to compare its FEP address and Compton suppression ratio. Second, the case of the well-shaped and annular-shaped secondary scintillators is compared, respectively, to find out their impact on energy resolution and FEP address. The final results show that, compared with the ACP detector using a φ75 × 90 mm2 LaBr3:Ce/NaI:Tl cylindrical composite scintillator, a truncated cone-shaped composite scintillator of 0.8 inclination may have an equivalent 137% light yield (137% signal-to-noise ratio), a Compton suppression ratio of 89.62% (at 662 keV), 89.98% FWHM energy resolution, and a volume reduction of 36.74%, which means that the weight of the detector is reduced by 2.107 kg. [ABSTRACT FROM AUTHOR]

A new fibre-sampling dual-readout calorimeter prototype has been qualified on beam at two facilities (DESY and CERN) using electrons from 1 to 100 GeV. The prototype was designed to almost fully contain electromagnetic showers and a central module (highly granular readout) was equipped with 320 Silicon Photomultipliers (SiPMs) spaced by 2 mm and individually read out. The test beams performed in 2021, allowed to qualify the readout boards used to operate the SiPMs, to define the calibration procedure and to measure the light yield for scintillating and Cherenkov signals produced by the shower development. This paper reports the first results obtained with the highly granular readout and discusses the ongoing R&D to address some open questions concerning the mechanical integration and the scalable readout scheme that will allow to build and operate the next prototype designed for hadronic showers containment. [ABSTRACT FROM AUTHOR]

Scintillators play an important role in radiation detection and imaging. Thallium-doped cesium iodide (CsI:Tl) and sodium iodide (NaI:Tl) are two of the major scintillators that have been used for many applications for many decades. In this paper, we will present an improved scintillation performance of Bridgman method-grown CsI(Tl) and NaI(Tl) crystals developed by Xtallized Intelligence, Inc. (XI, Inc.), and we will compare the performance with commercially available CsI:Tl and NaI:Tl. In a preliminary testing using MicroFJ−60035−TSV silicon photomultipliers (ON Semiconductor), the newly developed and improved 12.5 × 12.5 × 6 mm3 CsI:Tl crystal has shown an energy resolution of 4.8% (FWHM) at 662 keV, compared to 7.2% obtained by a commercially available CsI:Tl with a size of 12.5 × 12.5 × 25 mm3. The energy resolution of 5.4% (FWHM) at 662 keV is obtained for the newly improved NaI:Tl crystal, compared to 7% obtained by a commercially available ∅1″ × 1″ NaI(Tl). The comparison of the photo peak channel locations shows that the improvements in both CsI:Tl and NaI:Tl, developed by XI, Inc., have produced much larger signal amplitudes (roughly double), when compared to the commercially available CsI(Tl) and NaI:Tl. Improved decay time constants are presented as well. [ABSTRACT FROM AUTHOR]

It is important to differentiate between natural and artificial radioactive materials such as plutonium in nuclear facilities. In this study, a scintillator-based alpha-particle detector was developed using YAP:Ce scintillator and Multi-Anode PhotoMultiplier Tube. The detector was used to measure various naturally occurring radioactive materials (NORM) samples including radon progeny, lead plate, lantern mantle, and radium ceramic ball. The measurement results were compared with Monte Carlo simulation calculations and were found to be in agreement. The energy resolution of the detector is 8.6%FWHM. In the measurement results of radon progeny, peaks of 212Bi (6.1 MeV), 214Po (7.7 MeV), and 212Po (8.8 MeV) can be observed. The lead plate contains 210Po and emits 5.3 MeV alpha particle. The simulation with the same energy was able to reproduce the actual measurement. The results showed the energy and distribution of the alpha particles emitted by the NORM samples. The study successfully demonstrated the capability of the developed alpha-particle detector in identifying NORM. [ABSTRACT FROM AUTHOR]

CYGNO is an international collaboration with the aim of operating a ▪ optical time projection chamber (TPC) for directional Dark Matter (DM) searches and solar neutrino spectroscopy, to be deployed at the Laboratori Nazionali del Gran Sasso (LNGS). A ▪/▪ (60/40) mixture is used, along with a triple Gas Electron Multiplier (GEM) cascade to amplify the ionisation signal. The scintillation produced in the electron avalanches is read out using a scientific complementary metal–oxide–semiconductor (sCMOS) camera. This solution has proven to provide very high sensitivity to interactions in the few ▪ energy range. The inclusion of a hydrogen-based gas will offer an even lighter target, resulting in a more efficient energy transfer in a DM particle collision, and consequently, a lower detection threshold. Additionally, longer track lengths of light nuclear recoils are easier to detect with a clearer direction. However, the addition of such gas will contribute to quenching the scintillation, jeopardizing the TPC performance. In this work, we demonstrate the feasibility of adding 1% to 5% isobutane to the ▪/▪ (60/40) mixture by measuring the respective absolute scintillation yield output. The overall scintillation produced in the charge avalanches is not drastically suppressed by quenching due to the isobutane addition. The presence of Penning transfer from excited He atoms to isobutane molecules increases the number of electrons in the avalanches, partially compensating for the loss of scintillation due to quenching. For the highest applied GEM voltage, the total number of photons produced in the avalanche per ▪ deposited in the absorption region presents a decrease of only a factor of about three, from 2.30 (20) × 10 4 to 8.2 (4) × 10 3 ▪, as the isobutane content increases from 0 to 5%. The quantification of the visible component of the scintillation shows that isobutane quenches both visible and ultraviolet (UV) photons emitted by ▪/▪. [ABSTRACT FROM AUTHOR]

The discrimination of α / β -particles based on Liquid Scintillation (LS) is a measurement technique that can be applied for environmental monitoring. This technique relies on the specific feature of the scintillation process yielding two decay components (fast and delayed) of the photon emission following a particle interaction in a LS sample; indeed, the intensity of the delayed component is higher for α -particles than for β -particles. When operating with a photon detector such as a PhotoMultiplier Tube (PMT), the Pulse-Shape Discrimination (PSD) is the traditional approach, relying on low-pass filtered signals allowing pulse-tail analysis for an α -particle identification. This paper presents a new α -particle detection method based on an Artificial Neural Network (ANN) that directly processes fast pulse trains produced by the delayed scintillation component of a single detector. The ANN is trained using an experimental dataset obtained with a single PMT channel connected in a 3-PMTs detection system from which triple coincidences resulting from α -interactions ( 241 A m) in a LS source are used for the single detector labeling. As we target a real-time implementation, the ANN is designed to minimize the computational resources. The classifier can operate with good performances (91.0% of correct classification, 8.5% false negative and 0.5% false positive) on a single-channel detector. [Display omitted] • Focus on the photons train from a scintillator instead of the integrated pulse shape. • α / β discrimination relying on an ANN which analyses the signal from a single PMT. • Training dataset labelization based on coincidence detection. • The coïncidence detection is performed using a 3-PMT TDCR experimental layout. [ABSTRACT FROM AUTHOR]

Composite materials consisting of 6Li scintillator particles in an organic matrix can enable thermal neutron detectors with excellent rejection of gamma-ray backgrounds. The efficiency of transporting scintillation light through such a composite is critical to the detector performance. This optical raytracing study of a composite thermal neutron detector quantifies the various sources of scintillation light loss and identifies favorable photomultiplier tube (PMT) readout schemes. The composite material consisted of scintillator cubes within an organic matrix shaped as a right cylinder. The cylinder surface was surrounded by an optical reflector, and the light was detected by PMTs attached to the cylinder end faces. A reflector in direct contact with the composite caused 53% loss of scintillation light. This loss was reduced 8-fold by creating an air gap between the composite and the reflector to allow a fraction of the scintillation light to propagate by total internal reflection. Replacing a liquid mineral oil matrix with a solid acrylic matrix decreased the light transport efficiency by only ∼10% for the benefit of creating an all-solid-state device. The light propagation loss was found to scale exponentially with the distance between the scintillation event and the PMT along the cylinder main axis. This enabled a PMT readout scheme that corrects for light propagation loss on an event-by-event basis and achieved a 4.0% energy resolution that approached Poisson-limited performance. These results demonstrate that composite materials can enable practical thermal neutron detectors for a wide range of nuclear non-proliferation and safeguard applications. [ABSTRACT FROM AUTHOR]

A new neutron time-of-flight (nTOF) detector for deuterium–deuterium (DD)-fusion yield and ion-temperature measurements was designed, installed, and calibrated for the OMEGA Laser Facility. This detector provides an additional line of sight for DD neutron yield and ion-temperature measurements for yields exceeding 1 × 1010 with higher precision than existing detectors. The nTOF detector consists of a 90-mm-diam, 20-mm-thick BC-422 scintillator and a gated Photek photomultiplier tube (PMT240). The PMT collects scintillating light through the 20-mm side of the scintillator without the use of a light guide. There is no lead shielding from hard x rays in order to allow the x-ray instrument response function of the detector to be measured easily. Instead, hard x-ray signals generated in implosion experiments are gated out by the PMT. The design provides a place for glass neutral-density filters between the scintillator and the PMT to avoid PMT saturation at high yields. The nTOF detector is installed in the OMEGA Target Bay along the P8A sub-port line of sight at a distance of 5.3 m from the target chamber center. In addition to DD measurements, the same detector can be used to measure the neutron yield and ion temperature from deuterium–tritium (DT) implosion targets in the 5 × 1010 to 2 × 1012 yield range. The design details and the calibration results of this nTOF detector for both D2 and DT implosions on OMEGA will be presented. [ABSTRACT FROM AUTHOR]

The Tile Calorimeter (TileCal) is the central hadronic calorimeter of the ATLAS experiment at the LHC. This sampling device is made of steel plates acting as absorber and scintillating tiles as active medium. The wavelength-shifting fibers collect the light from scintillators and carry it to the photomultiplier tubes (PMTs). The analogue signals from the PMTs are amplified, shaped and digitized by sampling the signal every 25 ns and stored on detector until a trigger decision is received. The TileCal front-end electronics read out the signals produced by 9852 channels, whose dynamic range covers the interval from 30 MeV to 2 TeV. Each stage of the signal propagation from scintillation light to the signal reconstruction is monitored and calibrated. During LHC Run-2, high-momentum isolated muons and isolated hadrons have been used to study and validate the electromagnetic scale and the hadronic response, respectively. The time resolution was studied with multi-jet events. Results of performance studies that address calibration, stability, energy scale, uniformity and time resolution are presented. [ABSTRACT FROM AUTHOR]

This work presents a novel stereo coded aperture gamma camera based on four detection modules placed within four quadrants. Each module includes 48 × 48 strips of Bi4Ge3O12 scintillators, 24 × 24 pieces of silicon photomultipliers (SiPMs), and a set of data acquisition circuits. All signals from the SiPMs are individually extracted and finally simplified into 144 outputs to calculate the positions and energies of gamma-rays. Two masks of modified uniformly redundant arrays are fixed in the front of the top-right and bottom-left modules and two anti-masks are fixed in the top-left and bottom-right modules to achieve simultaneous imaging without dual measure. Once the projections of radioactive sources are determined, their source-to-detector distances can be estimated by our new multocular ranging algorithm. A series of lab and field experiments, including flood histogram and energy spectrum testing, field-of-view and angular resolution testing, real-time imaging, long-distance imaging, and ranging ability testing, with different radioactive sources, such as 137Cs, 22Na, 241Am, 60Co, 133Ba, and 75Se, have been completed to evaluate the comprehensive ability of the stereo gamma camera. The results show that the stereo gamma camera has a strong ability for the three-dimensional localization of radioactive sources over long distances with a high image sensitivity. So far, the stereo gamma camera has been successfully used in practical nuclear security and safety tasks although the angular resolution and the ranging algorithm robustness should be more optimized in the future. [ABSTRACT FROM AUTHOR]

This work shows a study of the effect of the non-uniformity of photocathode response on the energy resolution of plastic scintillators optimized for pulse-shape discrimination. The studies were performed with Hamamatsu R7600U-200 and R9779 photomultiplier tubes. The pulse-height and pulse-shape spectra were obtained for a small piece of radon-222 loaded plastic scintillator positioned at different places on the photocathode. We show that alpha spectra can be approximated well with a normal distribution if the non-uniformity of the photon response of the photocathode is minimized. In the cases when the non-uniformity cannot be minimized, we propose an analytical function which describes the shape of the alpha peaks well under a variety of conditions. A possible effect of the non-uniformity of the photocathode response on the primary activity measurements by liquid scintillation counting is highlighted. [ABSTRACT FROM AUTHOR]

Most of scintillators used for radiation detection exhibit afterglow, which is emission of light with longer decay times than that of main light pulse. High signal from afterglow has usually negative influence on detection parameters, e.g. for energy resolution in spectrometry measurements. The paper deals with long-term afterglow of some types of scintillators, which is more significant in the case of integral measurement when current in the photodetector is measured. The range of studied decay times was in the order of tens of seconds to days. Seven types of scintillators were measured: BGO, CaF2(Eu), CdWO4, CsI(Tl), LiI(Eu), NaI(Tl) and plastic scintillator. Excitation of scintillators was made using a UV lamp. After UV irradiation, a scintillator was inserted to scintillation detection unit and the anode current of photomultiplier tube was measured with a picoammeter. As results, CaF2(Eu) and plastic scintillator have relatively low long-term afterglow signal compared with other measured scintillators. [ABSTRACT FROM AUTHOR]

Sodium iodide crystal co-doped with thallium and lithium is a promising scintillator with wide application prospects for dual gamma neutron detection. In this study, a compact gamma/neutron detector was developed based on 2-inch NaI(Tl+Li) (NaIL) scintillator readout with 8 × 8 silicon photomultiplier (SiPM) array. Dedicated transimpedance amplifier circuit was developed for the SiPM array. The energy resolution and response linearity with the SiPM array were evaluated and compared to those obtained with photomultiplier tube (PMT) readout. The energy resolution for 661.6 keV gamma rays was measured as 7.0% and 6.5% with SiPM array and PMT, respectively. The linear response of the SiPM array is almost the same as that of the PMT in the energy range up to ~4 MeV. Neutron and gamma pulse shape discrimination was evaluated by acquiring the pulse waveforms with a digitizer (12 bit/250 MSPS) and off-line analysis. The best figure of merit (FOM) was measured as 3.75 for the SiPM array with optimized parameters, close to the performance measured with PMT (FOM = 4.07). The experimental results show that the NaIL scintillator readout with SiPM array exhibit energy resolution equivalent to NaI(Tl) gamma detectors and excellent neutron/gamma discrimination, making it especially suitable for compact devices requiring gamma and neutron dual detection capabilities. [ABSTRACT FROM AUTHOR]

A majority of the silicon photomultipliers (SiPMs) are sensitive to blue and near-ultraviolet (NUV) photons that are not optimized for scintillators with the emission maximum at wavelengths longer than 500 nm. The red–green–blue (RGB) SiPM is developed for the maximum photon detection efficiency (PDE) at 550 nm, which is a good match for some high-light-yield scintillators, such as CsI:Tl (CsI) and Gd1.5Y1.5Ga2Al3O12:Ce (GYGAG). Comparisons are made for the performance of these scintillators coupled to the RGB SiPM and a blue-sensitive SiPM. Because it takes tens of nanoseconds for the microcells to recharge after registering a photon hit, the linearity of these scintillation detectors was studied for high-energy gammas where numerous scintillation photons are generated. In addition, the energy resolution of the 662-keV gamma emitted by 137Cs was measured for temperatures between −20 °C and 50 °C. The nonlinearity was observed above 1 MeV for all measurements, and however, it can be corrected by energy calibration using a third-degree polynomial. For CsI, the energy resolution is better with the blue-sensitive SiPM because of the lower dark count rate (DCR). In contrast, GYGAG coupled to the RGB SiPM has a better energy resolution for temperatures below 30 °C because of the well-matched emission spectrum and PDE distribution. Nevertheless, the advantage disappears for temperatures above 30 °C due to the higher DCR. It would be useful to further develop the RGB SiPM with a lower DCR and higher operating temperatures. [ABSTRACT FROM AUTHOR]

Developments in the field of organic semiconductors have generated organic photodetectors with high quantum efficiency, wide spectral sensitivity, low power consumption, and unique form factors that are flexible and conformable to their substrate shape. In this work, organic photodetectors coupled with inorganic CsI(Tl) scintillators are used to showcase the low dose rate sensitivity that is enabled when high performance organic photodetectors and scintillator crystals are integrated. The detection capability of these organic-inorganic coupled systems to high energy radiation highlights their potential as an alternative to traditional photomultiplier tubes for nuclear spectroscopy applications. When exposed to Bremsstrahlung radiation produced from an X-ray generator, SubPc:C60, AlPcCl:C70, and P3HT:PC61BM thin film photodetectors with active layer thicknesses less than 100 nm show detection of incident radiation at low and no applied bias. Remarkably low dose rates, down to at least 0.18 μGy/s, were detectable with a characteristic linear relationship between exposure rate and photodetector current output. These devices also demonstrate sensitivities as high as 5.37 mC Gy-1cm-2 when coupled to CsI(Tl). Additionally, as the tube voltage across the X-ray generator was varied, these organic-inorganic systems showed their ability to detect a range of continuous radiation spectra spanning several hundred keV. [ABSTRACT FROM AUTHOR]

The effect of pulse pile-up on neutron count rates is a persistent challenge in photon active interrogation. During active interrogation, the neutron signatures from illicit special nuclear material (SNM) can provide a characteristic signal; however, the intense radiation environment can cause pulse pile-up in detectors. Organic scintillator detectors are favorable in active interrogation due to their fast neutron efficiency and fast timing characteristics and rely upon pulse shape discrimination to compare pulse shapes and classify detection events. Pile-up events are typically rejected during the analysis process because the pile-up events result in pulses with relatively large tail integrals, which appear similar to single neutron pulses. Pile-up events can be identified and removed in postprocessing, but in photon active interrogation scenarios, pile-up rejection algorithms can degrade due to the high pile-up rates, leading to erroneously high neutron count rates. Thus, it is essential that pulse pile-up events are minimized to produce accurate results. In this work, we compare the performance of a pair of 6-mm trans-stilbene cubes to a 5.08-cm-diameter, 5.08-cm-height trans-stilbene cylindrical detector during photon active interrogation. We use a Varex electron linear accelerator (linac) to produce an interrogation beam of bremsstrahlung photons up to 9 MeV in energy, which induces photofission and photodisintegration in depleted uranium (DU). We first optimize the pulse shape parameters for the 6-mm stilbene cubes using 137Cs and 252Cf sources and deploy the detectors in an active interrogation environment. As expected, the smaller detectors experience significantly less pile-up than the 5.08-cm stilbene cylindrical detector due to the reduction in detection volume. The 6-mm stilbene detectors observe a 250 ± 24 s−1 net neutron count rate and could determine the presence of the $\approx 2.8$ -kg DU in less than 3 min of measurement time, in stark contrast to the 5.08-cm stilbene detectors that failed to identify a net increase in neutron count rate due to the significantly high proportion of pile-up pulses. This work demonstrates that small detectors are robust against pile-up in photon active interrogation scenarios while maintaining a satisfactory neutron detection efficiency. [ABSTRACT FROM AUTHOR]