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Nuclear imaging techniques rely on the accurate positioning of events to produce the final images. Among the factors affecting the event positioning accuracy is the nonuniform light distribution between different regions of gamma detectors. In this article, we attempt to implement the adaptive neuro-fuzzy inference system (ANFIS) as a scintillation event positioning algorithm to improve the linearity and uniformity of the response. Therefore, we trained the network using signal data collected from a monolithic scintillator coupled to a position-sensitive photomultiplier tube (PS-PMT). We evaluated the position detection performance of the system after convergence with a test dataset. The results showed a 1.149-mm RMSE and over 98% $R^{2}$ value for position estimation. Moreover, the average full-width at half-maximum (FWHM) values obtained by ANFIS were 1.18 and 1.57 mm for the $x$ - and $y$ -axes, respectively. Therefore, the implementation of ANFIS as a position estimation algorithm can minimize the limitations of the edge distortion effect in the final results. [ABSTRACT FROM AUTHOR]

In medical dosimetry, the radiation quantity of interest is frequently the dose to tissue. To make direct dosimeters that show the dose absorbed in soft tissue, tissue-equivalent material is preferred. Plastic scintillators (PLSs) are made of materials with a density similar to soft tissue and relatively have energy independent response. Non-proportionality must be taken into account when reproducing the light output spectrum for photons below 200 keV, as it reduces light output significantly. In comparison to a standard PLS, both low and high-energy photons’ pulse height distribution spectra as a result of lead doping were measured and calculated. The effect of a 0.5% lead doping scintillator is sufficient to make up for the loss or difference between soft tissues and PLSs in response to low-energy photons, particularly below 200 keV. [ABSTRACT FROM AUTHOR]

In this work, we report polyvinyl toluene (PVT)-based plastic scintillators highly loaded with five different kinds of organotin compounds. The newly developed Sn-loaded plastic scintillators demonstrate the capability of gamma spectroscopy detection with fast decay characteristics. The maximum of organotin loading ratio of 33 wt% (10.8 wt% Sn) was achieved in tributyl(1-ethoxyvinyl) tin. PVT plastic scintillators containing 20 wt% tributyl(1-ethoxyvinyl) tin have optimal performance, providing gamma-ray spectroscopy with a light yield of 7100 photons/MeV and an energy resolution of 11.7% at 662 keV. [ABSTRACT FROM AUTHOR]

NaI(Tl) scintillators can detect thermal neutrons with surprising efficiency, even in the presence of ambient gamma radiation. This is due to a peculiarity of the 128I level scheme. Deexcitation cascades following neutron captures in 127I, a main constituent of NaI with quite large neutron capture cross section, unexpectedly often involve the 167.4 keV state of 128I with 175 ns half-life, which feeds another isomeric level at 137.9 keV having a half-life of 845 ns. The 29.5 keV transition between both levels, as well as the subsequent deexcitation sequence to ground state comprising 137.9 keV sum energy, are almost certainly absorbed in the crystal. Signals including three scintillation pulses within few microseconds, the first one caused by a prompt part of the cascade, the second and third one disclosing 30 and 138 keV energy depositions and characteristic delays, are clearly related to such neutron captures. Double-pulse sequences comprising only the primary pulse and a delayed 138 keV signal are also distinctive but more prone to load-dependent background by random pulse pileups. This article demonstrates neutron detection with a Ø2” $\times2$ ” NaI(Tl) scintillation detector by finding and analyzing such double- and triple-pulse sequences in digitized detector signals. It quantifies effect and background rates as a function of the detector load ranging up to 30 kcps. Complementary measurements with a 6Li codoped Ø2” $\times2$ ” NaI(Tl) (NaIL) scintillator allow relating the neutron detection yield by delayed-coincidence counting to the 6Li capture rate in the same crystal and thus to evaluate prospects and limits of this technique. [ABSTRACT FROM AUTHOR]

An active shield using a scintillator and silicon photo-multipliers (SiPMs) has been developed to operate with space environment particle detectors sensitive to both protons and electrons, such as Influence sur les Composants Avancés des Radiations de l’Espace-Nouvelle Génération (ICARE-NG). The method shows a reduction in electron contamination through the sides of the detector, thus increasing energy resolution. Two geometries are studied, one working in coincidence mode with the main detector and the other in anti-coincidence. Performances of both the geometries are simulated in proton and electron environments in energy ranges typical of a space environment. Experimental measurements then aimed to validate the Monte Carlo simulation framework for scintillating materials. Finally, a case study of electron decontamination is carried out, as well as an error rate estimation in flux reconstruction. [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]

The radioluminescence (RL) response under X-rays is investigated for five different types of multimode silica-based optical fibers doped with Ge, P, Al, F, or Ce. The results indicate that all tested fibers show a measurable RL signal at dose rates from 0.1 to 15 Gy(SiO2)/s, using 10-cm-long samples and a photomultiplier-based acquisition chain. Other influences of radiation, such as radiation-induced attenuation, are discussed in order to evaluate the potential of such fiber types for radiation detection or dosimetry applications. [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]

The optically segmented single volume scatter camera (OS-SVSC) aims to image neutron sources for nuclear nonproliferation applications using the kinematic reconstruction of elastic double-scatter events. We report on the design, construction, and calibration of one module of a new prototype. The module includes 16 EJ-204 organic plastic scintillating bars individually wrapped in Teflon tape, each measuring $0.5 {\mathrm {cm}}\times 0.5 {\mathrm {cm}}\times 20 {\mathrm {cm}}$. The scintillator array is coupled to two custom silicon photomultiplier (SiPM) boards consisting of a $2\times 8$ array of SensL J-Series-60035 SiPMs, which are read out by a custom 16 channel DRS4 based digitizer board. The electrical crosstalk between SiPMs within the electronics chain is measured as $0.76\% \,\pm \,0.11\%$ among all 16 channels. We report the detector response of one module including interaction position, time, and energy, using two different optical coupling materials: EJ-560 silicone rubber optical coupling pads and EJ-550 optical coupling grease. We present results in terms of the overall mean and standard deviation of the $z$ -position reconstruction and interaction time resolutions for all 16 bars in the module. We observed the $1\sigma z$ -position resolution for gamma interactions in the 0.3–0.4 MeVee range to be 2.24 cm ± 1.10 cm and 1.45 cm ± 0.19 cm for silicone optical coupling pad and optical grease, respectively. The observed $1\sigma $ interaction time resolution is 265 ps ± 29 ps and 235 ps ± 10 ps for silicone optical coupling pad and optical grease, respectively. [ABSTRACT FROM AUTHOR]

In recent years, a number of new scintillator materials with improved energy resolution for gamma-ray detectors have become commercially available for use in terrestrial-based homeland security applications, and some are being incorporated into instrumentation for space. Unlike terrestrial applications, the harsh environment of space—in particular, energetic trapped particles, cosmic rays, and neutrons—often activates these materials, and any improvement in sensitivity as a result of improved energy resolution could be offset by the additional background due to activation. The purpose of this work was to measure potential backgrounds due to trapped and cosmic-ray proton-induced activation in the new materials: SrI2:Eu (SrI), 7Li-enriched Cs2LiYCl6:Ce (CLYC-7), Cs2LiLaBr6:Ce (CLLB), Cs2LiLa(Br,Cl)6:Ce (CLLBC), Tl2LiYCl6:Ce (TLYC), and Gd3(Al,Ga)5O12:Ce (GAGG). Using a large-diameter 64-MeV proton beam, detectors were irradiated with a total dose of 100 rad (Si), roughly equivalent to the annual dose in a typical low earth orbit. Measurements were made with a single 100% relative efficiency high-purity germanium (HPGe) (0.05–3 MeV) and the irradiated detector. Two multichannel analyzers (MCAs) operating in the event mode were used to collect the data. Time-tagged events were processed into various spectral integration times for analysis, and characteristic gamma-ray energies and decay times were used to identify activation products. Most of the identified activation products were the result of (p, xn) reactions, with a few exceptions. This work identifies the primary radioisotopes generated by energetic proton activation in six different scintillator materials. [ABSTRACT FROM AUTHOR]

Localizing and quantifying special nuclear materials (SNMs) is desired for effective nuclear security and robust nuclear power management. Here, we demonstrate a compact radiation imaging system based on a coded aperture that allows one to form a quantified radionuclide distribution map for small amounts of SNM. The imager is based on the active scintillating medium: cerium-doped gadolinium aluminum gallium garnet [Gd3Al2Ga3O12(Ce) or GAGG(Ce)], which even in arrayed form exhibits excellent detection efficiency and good energy resolution over a wide energy range. With a $12 \times12$ array of $4\times 4\times20$ mm3 pixels, the instrument can image, at a target-to-imager separation of 1 m, 1 g of highly enriched uranium (HEU) in 4 min, 75 g of depleted uranium (DU) within 11 min, and 100 g of uranyl nitrate hexahydrate (UNH) within 11 min. The instrument, termed EPSILON-G, can also measure the ambient dose equivalent, H*(10), for radionuclides inside the unit’s 45° field of view (FOV), allowing one to accurately reconstruct the radiation dose map inside buildings. The system provides a precise determination of the H*(10) within a short acquisition time when compared to a Geiger–Muller (GM) survey meter due to the sizable area of the GAGG(Ce) scintillator array and its high density and $Z_{\text {eff}}$. Furthermore, one can identify, in real time, by means of gamma-ray detection, the accurate locations of neutron-gamma sources, as demonstrated with mixed emitters 252Cf, 239PuBe, and 241AmLi all while maintaining a gamma-ray analytical capability. [ABSTRACT FROM AUTHOR]

The Nevada National Security Site (NNSS), together with Los Alamos National Laboratory (LANL) and Lawrence Livermore National Laboratory, is developing a novel diagnostic to measure the reactivity of subcritical experiments (SCEs). This capability is known as neutron-diagnosed subcritical experiments (NDSEs). The decay of the fission gamma rays from the neutron-interrogated SCE is measured as a function of time with a large ($\sim 3$ -m diameter) detector wall consisting of 151 individual detector pixels. The data from this current mode measurement inform the neutron multiplication factor, $k_{\mathrm {eff}}$ , and thus the relative reactivity of the SCE. The NNSS developed the Gamma Array Simulation Toolkit (GAST) initially to help inform the design of the individual detector pixels and the 3.4-m diameter detector wall to be fielded as part of NDSEs. This toolkit is now being used to simulate and predict the performance of the final design of the individual detector pixels and the aggregate detector wall. Key detector characteristics evaluated from these simulations include impulse response, pulse height spectrum, number of photoelectrons per MeV, detector efficiency, and crosstalk between detector pixels. Collectively, the results of these simulations inform how well the fission gamma-ray die-off distribution from an NDSE measurement can be resolved. This is critical to determining the relative reactivity of the experiment. Furthermore, the GAST can be used to aid in the analysis of the experimental data from an NDSE measurement once the simulation has been benchmarked. [ABSTRACT FROM AUTHOR]

A dual-particle imager based on a rotational modulation collimator (RMC) utilizing a Cs2LiYCl6:Ce (CLYC) scintillator was developed and investigated for its dual-particle imaging performance. Design considerations and previous simulation work were verified by conducting experiments, and experimental results showing neutron and gamma-ray imaging capabilities were obtained. The imaging performance of the CLYC-based RMC system was further evaluated by investigating it in a mixed neutron and gamma-ray environment, and dual-particle imaging capability of the RMC system was demonstrated. Signal-to-noise ratio (SNR) values larger than 45 were achieved for reconstructed images of each neutron and gamma-ray source distribution, if modulation patterns were obtained with average fractional counting uncertainty of less than 3%. The structural similarity (SSIM) index of reconstructed images was calculated to be almost unity, indicating an artifact-free image. [ABSTRACT FROM AUTHOR]

Oak Ridge National Laboratory is developing a portable, pixelated fast-neutron imaging panel for associated particle imaging (API). The panel consists of new and commercially available hardware. Unlike the current generation of API-based neutron imaging systems, this panel is intended to be field deployable. A $30\times30$ array of optically isolated 1 cm $\times$ 1 cm $\times$ 5 cm pulse shape discriminating (PSD) plastic scintillator pixels are optically coupled to a $6\times6$ array of position-sensitive photomultiplier tubes (PMTs) allowing each pixel to be resolved. Each quadrant of $3\times3$ PMTs recombines the 576 PMT anodes using a resistive charge division network to achieve four-corner readout that preserves the average position of the detected light. The design of the panel and initial testing of the light collection and position encoding electronics is presented herein. [ABSTRACT FROM AUTHOR]

Upgrades to the Spallation Neutron Source at Oak Ridge National Laboratory will provide a second target station and an increased neutron flux, which will offer a more powerful tool for neutron reflectometry. To fully utilize the higher neutron flux, a high-speed, neutron-imaging device (an imaging plane) specifically for reflectometry is required. The neutron imaging plane requires a detection efficiency of 60% for 2 Å neutrons for event rates exceeding 2 Mcps/cm2 with less than 10% dead time. A novel organic glass scintillator material loaded with a boron compound demonstrated good neutron sensitivity. Simulations show that the detection efficiency for thermal neutrons can reach 60% with a 500- $\mu \text{m}$ thickness, if the glass is loaded with 99% enriched $^{10}\text{B}$ compound at 10% wt. A lower concentration of 95% enrichment at 5% wt loading can provide 60% efficiency with a thickness slightly above 1 mm. The decay time of the scintillator is less than 100 ns, providing a fast response for high rate counting. The instrument design is based on detecting the neutron with a fast scintillation material and integrating silicon photomultipliers (SiPMs) with high-speed digital electronics. Traditional pulse sampling using a high-speed analog to digital converter (ADC) to conduct pulse shape discrimination is not viable for imaging, and a new technique has been formulated for this material using a time over threshold (TOT) method to isolate neutrons from gamma-ray interactions. The gamma-neutron peak separation is greater than two sigma, and with a thin scintillator, the gamma-ray rejection per detected neutron should meet the design specification of $10^{-6}$. Using the TOT method, the digital information to be processed by an interfacing ADC is reduced allowing for readout per SiPM, providing a position resolution close to 1 mm. [ABSTRACT FROM AUTHOR]

In this work, we propose a prototype of a compact detector assembly capable of discriminating between neutrons and gamma rays, by performing pulse shape analysis. The device takes advantage of recent improvements in silicon photomultiplier (SiPM) technology and the excellent neutron/gamma-ray discrimination capabilities of new plastics and standard liquid scintillators. Our work is focused on the read-out of small-, medium-, and large-sized organic scintillators with large-area SiPM arrays ($4 \times 4$ NUV and RGB-SiPM arrays, 17 mm $\times$ 17 mm). In particular, we used EJ-276 (and its old version EJ-299) and EJ-276G plastic scintillators of several sizes (ranging from 20- to 50-mm diameter) and two large liquid scintillator cells (EJ-301 and EJ-309, 50 mm diameter $\times 50$ mm thickness). Moreover, we show the comparison of neutron/gamma-ray discrimination performance between SiPM and standard photomultiplier read-out configurations. The presented innovative device could be used in different fields, first in fundamental nuclear physics experiments, as an ancillary neutron detector for the active target at the selective production of exotic species (SPES) facility at the Legnaro National Laboratories in Italy. Additionally, it could be used in radiation monitoring applications, as a fast neutron/gamma-ray counter to be embedded in unmanned vehicles for radiation monitoring. [ABSTRACT FROM AUTHOR]

Obtaining directional information is required in many applications such as nuclear homeland security, contamination mapping after a nuclear incident and radiological events, or during the decontamination work. However, many directional radiation detectors are based on directional shielding, made of lead or tungsten collimators, introducing two main drawbacks. The first is the size and weight, making those detectors too heavy and irrelevant for utilization in handheld devices, drone mapping, or space applications. The second drawback is the limited field of view (FOV), which requires multiple detectors to cover the whole required FOV or machinery to rotate the detector’s narrow FOV detector. We propose a novel $4\pi $ directional detector based on a segmented hollow cubic detector, which uses the Compton effect interactions with no heavy collimators. The symmetrical cubical design provides both higher efficiency and $4\pi $ detection ability. Instead of the traditional two types of detectors (scatterer and absorber) structure, we use the same type of detector, based on Gd3Al2Ga3O12 (GAGG) (Ce) scintillator coupled to silicon photomultiplier. An additional advantage of the proposed detector is obtained by locating the photon sensors inside the detector, behind the scintillators, which improves the radiation hardness required for space applications. Furthermore, such an arrangement flattens the temperature variation across the detector, providing better gain stability. The main advantage of the proposed detector is an efficient $4\pi $ radiation detection for high-energy gamma rays without the use of heavy collimators. [ABSTRACT FROM AUTHOR]

GYGAG(Ce) transparent ceramic garnet scintillators were irradiated with electrons from 0.5 to 2 MeV with fluences from $10^{16}\,\,\text{e}^{-}$ /cm2 to $10^{19}\,\,\text{e}^{-}$ /cm2, corresponding to doses from 0.3 to 310 Gigarad. Absorption spectra were measured before and after irradiations. Light yields from alpha, beta, and gamma excitations were measured before and after irradiation and compared to preirradiation values to gain a deeper understanding of how electron irradiations can affect light yield, as well as defects generated in both the surface and bulk. Within experimental error, no degradation in light yield was observed for the electron-irradiated samples, as measured via beta or gamma excitation, with minimal degradation observed via alpha excitation. A small increase in optical absorption near the wavelength of emission was observed following the largest dose irradiation. These results suggest that GYGAG(Ce) is radiation hard to electron irradiation up to $10^{19}\,\,\text{e}^{-}$ /cm2 and doses up to 310 Gigarad. This robustness to irradiation indicates that transparent ceramic garnets may prove useful for applications such as scintillation-based nuclear batteries by allowing for higher energy beta emitters, increased power densities, and enabling long service lifetimes. [ABSTRACT FROM AUTHOR]

Optical couplant greases based on polydimethylsiloxane (PDMS) may be employed in devices such as scintillator-based radiation detectors that operate in extreme environmental conditions. The optical transmission of Dow Corning DOWSIL Q2-3067 optical couplant grease was measured at room temperature as a function of wavelength (200–800 nm) and grease thickness (0.13–1 mm). Across the spectral range, transmission decreased with increasing thickness, and the increase was more pronounced at wavelengths < 400 nm. An effective ultraviolet (UV) cutoff wavelength of ~270 nm was found, independent of grease thickness, although a weak transmission feature was observed below this cutoff at 233 nm. The optical transmission spectra exhibited a dependence on temperature, increasing with increasing temperature to 50 °C and decreasing with decreasing temperature to −10 °C. This temperature dependence was more pronounced at wavelengths < 400 nm and for thicker grease layers. Below −10 °C, transmission decreased sharply for all wavelengths. This decrease was correlated with a sharp increase in viscosity, indicating that the grease undergoes a thermal transition at −11 °C ± 1 °C. This thermal transition occurs more slowly with decreasing temperature for thinner layers of grease, but all measured grease thicknesses were reasonably opaque at temperatures below −20 °C. These results will aid in predicting the optical and mechanical performance of optical systems such as radiation detectors exposed to extreme outdoor environmental conditions. [ABSTRACT FROM AUTHOR]

Polyvinyl toluene (PVT), with additives, is a widely used organic plastic scintillator that is robust and inexpensive for large-volume gamma-ray detectors. Even though PVT-based scintillators have been used for decades in many applications, some of their basic optical properties have not been fully explored. Measurements of the attenuation length, index of refraction, and scintillation light output of a specific commercial PVT-based scintillator (Saint-Gobain BC-412) as a function of temperature are presented. These properties are important to the performance of systems using PVT-based scintillators in environments subject to wide temperature variations and are being used to better model the performance of such applications. [ABSTRACT FROM AUTHOR]

This work addresses the use of plastic scintillators as an alternative to 3He neutron detectors for radioactive waste drum characterization. The time response of scintillators is three orders of magnitude faster than that of gas proportional counters, and they offer similar neutron detection efficiency at lower cost. However, they are sensitive to gamma rays and the neutron-gamma pulse shape discrimination (PSD) is not possible with standard PVT scintillators. The proposed approach uses the neutron and gamma times of flight in triple coincidences recorded with 252Cf, AmBe, and 60Co sources. A 2-D histogram of time delays between the second and first detected pulses, on the $x$ -axis, and between the third and second pulses, on the $y$ -axis, evidences a specific region of interest for spontaneous fission coincidences. MCNPX-PoliMi simulations are performed, which are in good agreement with previous experiments and allow for investigating the types of coincidences ($\gamma \gamma \gamma $ , nnn, $\gamma $ nn, $\gamma \gamma \text{n}$) and optimizing the rejection of neutron and gamma scattering crosstalk. The method was also experimentally tested with a 118-L mock-up drum filled with a metallic or an organic matrix, showing a correct estimation of the net fission signal up to an “alpha ratio” of 12 between fission and ($\alpha $ ,n) neutron emissions. Matrix and localization effects were also measured, showing a sensitivity (useful signal per gram of 240Pueq) for a homogeneous distribution of plutonium in the iron matrix about three times larger than in the wood matrix, due to neutron slowing-down in the latter. This difference can be taken into account by the prior knowledge of the matrix characteristics or by neutron and gamma attenuation measurements. In contrast, in case of a point source with an unknown position in the matrix, the relative localization uncertainty is 26% for the metallic drum, and 41% for the organic one. [ABSTRACT FROM AUTHOR]

Proton therapy is a cancer treatment technique currently in growth since it offers advantages with respect to conventional X-ray and $\gamma $ -ray radiotherapy. In particular, better control of the dose deposition allowing to reach higher conformity in the treatments causing less secondary effects. However, in order to take full advantage of its potential, improvements in treatment planning and dose verification are required. A new prototype of proton computed tomography scanner is proposed to design more accurate and precise treatment plans for proton therapy. Our prototype is formed by double-sided silicon strip detectors and scintillators of LaBr3(Ce) with high energy resolution and fast response. Here, the results obtained from an experiment performed using a 100-MeV proton beam are presented. Proton radiographs of polymethyl methacrylate (PMMA) samples of 50-mm thickness with spatial patterns in aluminum were taken. Their properties were studied, including reproduction of the dimensions, spatial resolution, and sensitivity to different materials. Structures of up to 2 mm are well resolved and the sensitivity of the system was enough to distinguish the thicknesses of 10 mm of aluminum or PMMA. The spatial resolution of the images was 0.3 line pairs per mm (MTF-10%). This constitutes the first step to validate the device as a proton radiography scanner. [ABSTRACT FROM AUTHOR]

We report the investigations made on the use of pixelated plastic scintillator (PS) and silicon photomultipliers (SiPMs) array applied to coded aperture gamma-neutron imaging. Specifically, verification of the ability of a multiplexing readout to discriminate and localize neutron interactions was studied. In its intended configuration, the gamma-neutron imager design consists of a coded aperture aligned with a matrix of $12\times12$ PS each coupled to a SiPM. The coded aperture is a rank 7 modified uniformly redundant array (MURA), composed of 1.2 cm of tungsten, with a surface area of 100.4 mm $\times100.4$ mm and placed at 5 cm from the detector. The pixelated PS is composed of polystyrene and standard fluorophores (20 wt% PPO, 0.03 wt% POPOP) loaded with a lithium carboxylate (Li $\alpha $ -valerate), which allows the triple discrimination between thermal neutrons, fast neutrons, and photons. Each pixel of PS has a dimension of 3.6 mm $\times3.6$ mm $\times3.6$ mm and they are separated from each other by 0.6 mm of polytetrafluoroethylene (PTFE). The photonic and electronic readout consists of the ArrayC-30035-144P SiPM from SensL, Cork, Ireland, connected to the diode coupled charge division readout from AiT. First, this neutron imager design was modeled and simulated using the MCNP6 Monte Carlo code. The encoding capability, field of view, and spatial resolution of the neutron imager were therefore evaluated by simulation. Then, we detailed the experimental setups implemented to demonstrate the feasibility of coupling pixelated PS to SiPM to localize radioactive sources and showed the results obtained. Finally, based on this position-sensitive gamma-neutron detector, a gamma-neutron imager was prototyped and tested. [ABSTRACT FROM AUTHOR]

Since the beginning of using liquid scintillators for gamma–neutron separation, there have been many articles dealing with long-term degradation, especially due to oxygen dissolved in the cocktail or presented during scintillator encapsulation. Oxygen is a well-known quenching agent causing a significant reduction of light yield. The effect of aging of liquid organic scintillators, namely EJ301, EJ309 (both Eljen Technology), and new custom-made cocktails based on 1-Phenyl-3-(2,4,6-trimethylphenyl)-2-pyrazoline and 2,5-Bis (5-tert-butyl-benzoxazol-2-yl)thiophene luminophores, were investigated for more than half a year. The research was focused on the Compton edge shifting of gamma particles since the position is proportional to the light yield of the selected scintillator. It was proven that all investigated cocktails suffered from different deterioration of the light yield in the investigated period, especially those containing a low concentration of luminophore. On the other hand, the gamma–neutron separation was improving up to the 100th day of measurement. Furthermore, the gamma–neutron separation was observed and quantified using figure of merit (FoM) for samples prepared and filled under normal and nitrogen atmosphere during the mentioned period. All stated parameters of liquid scintillator NE213 manufactured by Nuclear Enterprises Ltd. opened more than three decades ago were measured and used for comparison. It was observed that even after 30 years, this cocktail was still able to discriminate gammas from neutrons. [ABSTRACT FROM AUTHOR]

The drift of the acquired gamma spectra used in prompt gamma neutron activation analysis (PGNAA) has a large influence on the analysis accuracy. To address this problem, a set of digital algorithms for wide-region spectral stabilization was investigated. The spectra were first calibrated by using the nonlinear method, and the counts in each channel were corrected with cubic spline interpolation. Then, the corrected spectra were used for stabilization according to the established stabilization method. The experimental results showed a significant reduction in the maximum relative deviation of the peak position for both sodium iodide [NaI(Tl)] (7.26%–1.25%) and bismuth germanate oxide (BGO) (20.15%–2.91%) detectors. [ABSTRACT FROM AUTHOR]

Because of their potential low cost, bright light, and fast decay time, LuAG:Ce ceramic scintillators have attracted a broad interest in the high-energy physics community. One crucial issue for their application in future high-energy physics experiments is their radiation hardness against neutrons and protons expected at future hadron colliders. We report optical and scintillation performance of 1-mm LuAG:Ce ceramic samples doped with Mg2+ (and Ca2+) and their radiation damage induced by hadrons. While Mg2+ co-doping improves their light output, Ca2+ co-doping improves their fast to total (F/T) ratio. LuAG:Ce ceramic samples were irradiated at the Los Alamos Neutron Science Center (LANSCE), Los Alamos, NM, USA, by neutrons up to $6.7\times 10^{15}\,\,\text{n}_{\mathrm {eq}}$ /cm2 and by 24-GeV and 800-MeV protons at CERN PS-IRRAD up to $1.2\times 10^{15}$ p/cm2 and at LANSCE up to $2.3\times 10^{14}$ p/cm2, respectively. All samples show excellent radiation hardness with more than 90% of light after irradiation. The RIAC values induced by neutrons are found to be a factor of 2 smaller than lutetium–yttrium oxyorthosilicate (LYSO:Ce) crystals. The RIAC values induced by protons are also found a factor of 2 smaller than LYSO:Ce crystals in LuAG:Ce ceramic samples with good optical quality. Research and development will continue to develop LuAG:Ce scintillating ceramics with improved optical quality for future investigation. [ABSTRACT FROM AUTHOR]

Gamma/neutron dual detection has occupied significant territory in the field of homeland security and nuclear energy development. Cs2LiLaBr6 (CLLB) has shown both neutron/gamma dual-mode detection capability and excellent scintillation properties. Herein, we explored the Cs2LaBr5-LiBr phase diagram through powder X-ray diffraction (XRD) and differential scanning calorimetry (DSC) tests of synthesized polycrystalline materials. The Cs2LaBr5-rich side of the phase diagram is similar to a binary peritectic phase diagram, where the peritectic line (447 °C) extends to a LiBr content of 61%. The LiBr-rich side of the phase diagram resembles a binary eutectic phase diagram, where the eutectic point (395 °C) is located at 80% LiBr concentration. Guided by the phase diagram, CLLB ingots were designed to grow from the LiBr-rich side with different concentrations of LiBr. The scintillator properties of CLLB crystals were found to be deteriorated by the increasing defects with elevated LiBr contents. A concentration of LiBr around 55% was a preference for the growth of high-quality CLLB. A better understanding of the Cs2LaBr5-LiBr phase diagram benefits the growth of CLLB crystals and provides considerations for other halide double perovskites. [ABSTRACT FROM AUTHOR]

The ORION chipset, a full-custom multichip readout and processing electronics for the X- $\gamma $ -ray imaging spectrometer (XGIS) on-board the transient high-energy sky and early universe surveyor (THESEUS) space mission, is presented. The XGIS detection plane is arranged in a matrix of 10 $\times $ 10 detection modules, each one composed of 64 CsI(Tl) scintillation bars (4.5 mm $\times $ 4.5 mm $\times $ 30 mm) optically coupled at the top and bottom ends to two 8 $\times $ 8 monolithic silicon drift detector (SDD) matrices. The top SDD, exposed to the X-ray entrance window, performs the double function of low-energy X-ray detection as well as scintillator’s readout, together with the bottom SDD, providing detection and spectroscopic energy range from 2 keV up to 20 MeV. The need to achieve a high-energy resolution, as well as a high sensitive area on the detection plane, led to the development of a chipset organized to have a minimum-area analog readout chip placed in close proximity of the SDD (ORION-FE) and a mixed-signal back-end (ORION-BE) placed a few centimeters further on the back-end board for the additional signal processing and digitization. The multichip readout electronics integrates two dedicated analog processors for low-energy photons up to 30 keV (X-processor) and high-energy photons up to 5 MeV ($\gamma $ -processor), allowing a spectroscopy-grade resolution in the 4 decades energy band (2 keV–20 MeV) of the XGIS, with a simulated power consumption of 1.55 mW/pixel. The ORION prototype was bonded to two ~25 mm2 SDDs, and extensively characterized in terms of pulse shaping, pulse discrimination, and stretching functionality, as well as linearity, dynamic range, and spectroscopic resolution. An optimum equivalent noise charge (ENC) at −20 °C of 24.3 el. r.m.s. on the X-channel [212 eV full-width at half-maximum (FWHM) on Si], and 39.6 el. r.m.s. on the $\gamma $ -channel [3.7 keV FWHM on CsI(Tl)] has been recorded. [ABSTRACT FROM AUTHOR]

Nowadays, silicon photomultipliers (SiPMs) are extensively used for absorption of scintillation light in all types of scintillators in high-energy physics. Fast spread of SiPMs resulted in a rapid development of both analytical and Monte Carlo models. Models describe the response of these silicon integrated circuits. We introduce a novel Monte Carlo model of SiPM with a scintillator module that enables modeling the response of SiPM to dynamic scintillation processes. The model introduces several improvements over other models. This article focuses on the analysis of pulse shape discrimination (PSD) performance of SiPM-based scintillation systems since such techniques are often used to discriminate between incident particles of ionizing radiation. The algorithms for PSD are sensitive to the shape of the pulse and SiPMs have several mechanisms that influence the shape of the output pulse, such as bandwidth of the system, the presence of fast decay components, and the recovery time of individual microcells. Some of these mechanisms are not present in a classical photomultiplier, for instance, a recovery time or the fast decay component. We have analyzed the performance of three different PSD algorithms with three SiPMs (MicroFC-30020, MicroFC-30035, and MicroFC-30050) coupled with scintillators EJ-301 and EJ-276. Several conclusions are drawn from the analysis. The two most important ones are that optimized systems need to finetune their bandwidth and that scintillators with fast decay signals are better suited for photomultipliers with lower recovery time and vice versa. It is also shown that the classical charge comparison algorithm does not reach the performance of modern algorithms, for instance, frequency gradient analysis. [ABSTRACT FROM AUTHOR]

Gain amplitude modulation multichannel ASIC (GAMMA) is a 16-channel application specified integrated circuit (ASIC), designed in 0.35- $\mu \text{m}$ technology to read the charge provided by silicon photomultipliers (SiPMs) on a wide amplitude range. This chip was designed to satisfy the demanding requirements of the INFN the GAMMA project, where a 3” $\times3$ ” large lanthanum bromide crystal is to be read by SiPMs, aiming at state-of-the-art energy resolution. Because the energy range of the application is 100 keV–20 MeV, signals in a wide dynamic range (DR) have to be processed by the ASIC. This wide DR requirement raised the necessity of an adaptive gain change solution in order to guarantee a high signal-to-noise ratio together with a large full-scale range. While the ASIC input stage features a programmable static gain, the analog filtering channel exploits a self-triggered gated integrator stage with an automatically adjusted gain for each detected input current pulse; one of the following values is selected: 10, 2, or 0.83 [mV/pC]. The gated integrator gain is predictively adjusted before the circuit reaches saturation due to a time-gated threshold mechanism and provides negligible charge loss when the gain is switched (< 20 fC). A preintegration feature is also implemented in order to get rid of nonlinearity due to delays in the integration phase that could take place in a multi-ASIC system. The ASIC uses 5- and 3.3-V bias voltages, the overall power consumption being 280 mW. The ASIC was tested with a $12\times12$ SiPMs matrix coupled with a 3 inch LaBr 3, providing good spectroscopic performances (2.6% at the 137Cs photopeak emission energy of 662 keV), and was also tested irradiating the SiPMs with fast, bright NUV light pulses, in order to explore the ASIC wide range coverage while simulating the scintillation light emission of a lanthanum bromide crystal. [ABSTRACT FROM AUTHOR]

In the nuclear sciences and radiation detection fields, the differentiation between gamma-ray and neutron interactions inside a detector volume continues to be an area of active research. Historically, the primary mechanism for conducting particle identification has been pulse shape discrimination (PSD). However, almost all variations of this technique rely on only two factors: the area of the tail and the total area of the pulse. In the last decade, the emergence of advanced machine learning techniques, most specifically artificial neural networks (ANNs), offers a unique opportunity to capitalize on the entirety of the waveform. But such techniques appear highly reliant on the quality of datasets used for training. Our research addresses this challenge to quantify the relative performances of networks trained on a variety of datasets and subjected to the same test. Furthermore, we offer an analysis of the portability of a network trained on one detector to a similar detector. [ABSTRACT FROM AUTHOR]

We present an electrical analysis method for a gamma-ray imaging system based on a resistive network readout. Currently, the array numbers of scintillators and detectors in imaging systems are being increased to enhance the spatial resolution, and resistive network-based readout circuits are used to reduce the number of channels. However, a positioning process is required to identify the channel in which the signal has been generated, which causes positional distortion. For position correction, the positioning characteristics must be measured according to the readout circuit conditions. However, due to the scintillator’s radiation, measurement in a single channel is difficult. In this work, a current pulse is modeled to analyze the positional characteristics of different channels. A current pulse generator and an automatic channel-selection circuit are designed to input signals selectively to each channel. When the input signal duration is 1 $\mu \text{s}$ , the maximum amount of charge generated by the current pulse generator is approximately 1000 pC. Position errors of up to 88.47% are generated, depending on the gain of the preamplifier. Our proposed method can be used for the linearity analysis of preamplifiers and image position correction algorithms. [ABSTRACT FROM AUTHOR]

A 128-channel positron detection system will be constructed at Experimental Muon Source (EMuS) of China Spallation Neutron Source (CSNS) to conduct muon spin rotation/relaxation/resonance ($\mu $ SR) measurements. Each detector channel consists of a scintillator, a light guide, and a photomultiplier tube (PMT). The long light guide is bent to an “L” shape to propagate optical photons from the scintillator to the PMT. A series of Geant4 simulations and experiments has been performed to optimize the light collection performance of the L-bent detector. Geometry deformation induced by the bending process has been well modeled. Simulation results agree with the experimental tests. Accordingly, a novel hybrid wrapping method (scintillator with polytetrafluoroethylene (PTFE) and light guide with aluminum tape) has been developed to improve the amplitude of detector signals greatly. Compared to wrapping the detector with merely PTFE tapes or aluminum tapes, this method leads to an enhancement in light collection efficiency of 73% or 14%, respectively. Two optimally manufactured prototype detectors using the novel wrapping method have been tested at the ISIS Muon Facility. The beam tests demonstrated that the L-bent detectors can precisely measure the behavior of muon spins inside samples. Therefore, the L-bent detector design is competent for $\mu $ SR applications at CSNS/EMuS. [ABSTRACT FROM AUTHOR]

High-performance radiation detection materials are an integral part of national security, medical imaging, and nuclear physics applications. Those that offer compositional and manufacturing versatility are of particular interest. Here, we report a new family of radiological particle-discriminating scintillators containing bis(9,9-dimethyl-9H-fluoren-2-yl)diphe-nylsilane (compound “P2”) and in situ polymerized vinyltoluene (PVT) that is phase stable and mechanically robust at any blend ratio. The gamma-ray light yield increases nearly linearly across the composition range, to ~16 400 photons/MeV at 75 wt.% P2. These materials are also capable of performing $\gamma $ /n pulse shape discrimination (PSD), and between 20% and 50% P2 loading is competitive with the PSD quality of commercially available plastic scintillators. The 137Cs scintillation rise and decay times are sensitive to P2 loading and approach the values for “pure” P2. Additionally, the radiation detection performance of P2-PVT blends can be made stable in 60 °C air for at least 1.5 months with the application of a thin film of poly(vinylalcohol) to the scintillator surfaces. [ABSTRACT FROM AUTHOR]

Ground-level cosmic ray muon detections have various potential applications in the predictions of space and Earth weather variations and muon tomography. However, in order to push its practical applications, a low-power, low-cost, high-accuracy, and portable ground-level cosmic ray muon detection system needs to be developed. In this article, we present a high time-resolution and low-power readout integrated circuit (ROIC) for portable ground-level cosmic ray muon detection. The ROIC comprises preamplifiers, comparators, encoding modules, a delay-locked loop (DLL), and a data transfer module. The preamplifiers amplify the weak signals produced by the muon detector. The comparators convert the amplified signals into digital signals. The encoding modules extract and store the time information of the input pulses produced by the comparator, and the data transfer module transmits them to a microcontroller unit (MCU). A pulse edge detecting method using DLL clocks is employed to improve the time-resolution and limit the power consumption of the ROIC. A 32-channel prototype of the ROIC was designed and fabricated in a 0.18- $\mu \text{m}$ mixed-signal CMOS process. The main chip size is 11.4 mm2. A one-channel double-layer plastic scintillator muon detector was used to test the performance of the ROIC. A time-resolution of 1.0 ns was achieved with a system clock of 50 MHz, and the ROIC power consumption was measured at 1.9 mW/channel. Compared with existing muon readout electronics systems, the system using the proposed ROIC achieves high time-resolution and accuracy, with low power consumption and a smaller size, making it suitable for portable real-time cosmic ray muon detection. [ABSTRACT FROM AUTHOR]

The upgrade of the BESIII end cap time-of-flight (TOF) detector needs to achieve a ~40-ps time resolution level to provide high-performance reference time for beam testing. Fast silicon photomultiplier tubes (SiPMs) have excellent time characteristics and the transition time spread (TTS) can reach tens of picoseconds. Therefore, SiPMs are selected to replace the PMTs in T0 detectors. In this article, we describe that the time characteristics of a fast SiPM and T0 system were studied using a high-speed real-time oscilloscope. In order to obtain the optimal time resolution, coupling techniques of the plastic scintillators and SiPMs were studied. Single-ended coupling between a SiPM and a plastic scintillator can obtain the best time resolution. [ABSTRACT FROM AUTHOR]

These days, research on the classification of neutron/gamma waveforms in scintillators using pulse shape discrimination (PSD) techniques is a highly studied topic. Numerous methods have been explored to optimize this classification, with some of the most recent research being focused on machine learning techniques with excellent results. These approaches are mainly based on the use of 1-D convolutional neural networks (CNNs). In this field, field-programmable gate arrays (FPGAs) with high-sampling rate analog to digital converters (ADCs) have been used to perform this classification in real-time. In this work, we select a potential architecture and implement it with the help of the IntelFPGA OpenCL SDK environment. A shorter and C-like development of OpenCL enables a more straightforward modification and optimization of the network architecture. The main goal of this work is the evaluation of the needed resources and the obtained performance to prototype a complete solution in the FPGA. The FPGA design is generated as if it was connected to an ADC module streaming the data samples with the help of a Board Support Package developed for an IntelFPGA ARRIA10 available in an Advanced Mezzanine Card (AMC) module in an Micro Telecommunications Computing Architecture (MTCA.4) platform. The prototyped solution has been integrated into Experimental Physics and Industrial Control System (EPICS) using the nominal device support (NDS) model currently being developed by ITER. [ABSTRACT FROM AUTHOR]

Using the waveforms from a digital electronic system, an offline analysis technique on pulse shape discrimination (PSD) has been developed to improve the neutron–gamma separation in a bar-shaped NE-213 scintillator that couples to a photomultiplier tube (PMT) at each end. The new improved method, called the “valued-assigned PSD” (VPSD), assigns a normalized fitting residual to every waveform as the PSD value. This procedure then facilitates the incorporation of longitudinal position dependence of the scintillator, which further enhances the PSD capability of the detector system. In this article, we use radiation emitted from an AmBe neutron source to demonstrate that the resulting neutron–gamma identification has been much improved when compared to the traditional technique that uses the geometric mean (GM) of light outputs from both PMTs. The new method has also been modified and applied to a recent experiment at the National Superconducting Cyclotron Laboratory (NSCL) that uses an analog electronic system. [ABSTRACT FROM AUTHOR]

A 6LiF:ZnS(Ag)-based cold neutron detector with wavelength shifting (WLS) fibers and Silicon photomultiplier (SiPM) photodetector was developed at the NIST Center for Neutron Research. For neutron scattering applications at the NCNR, detector false positives severely diminish the quality of very faint neutron scatter patterns. Thermal noise generated by the SiPM significantly increases the likelihood of false positives by the detector/discriminator. This article describes and evaluates a digital real-time algorithm implemented on a field programmable gate array (FPGA) which quickly differentiates SiPM thermal noise and noise pulse pile-up from neutron signals. The algorithm reduces deadtime spent on examining noise pulses as well as reduces the number of false positives. [ABSTRACT FROM AUTHOR]

Plastic scintillators are widely used in particle detectors when precise timing information is required. As a basis for comparing different detectors, we use such a characteristic as the time resolution per 1 MeV detected energy, i.e., the expected time resolution assuming the deposited energy in the scintillator is equal to 1 MeV, and all the scintillation light is collected to the photosensor. In this work, we measure this parameter with BC422 plastic scintillator read out by different silicon photomultipliers (SiPMs). The best obtained value is about 6 ps, which is almost a factor of 3 better compared to our earlier result from 2012. Such an improvement represents the progress in the development of SiPMs made over these years and, driven by this progress, improved knowledge and know-how on such detectors. [ABSTRACT FROM AUTHOR]

A transimpedance amplifier (TIA) is an essential electronic circuit in prompt gamma detection. To improve the performance and reliability of the electronics, we designed a TIA using GaN high electron mobility transistor (HEMT) as it is more radiation-hardened when compared to its silicon counterpart and it has lower noise. Our circuit is designed using GaN HEMT from efficient power conversion (EPC) and has a 3-dB frequency of 21 MHz and 45 dB Ω of transimpedance gain. Its total output rms noise voltage is 3.1 mV. Its functionality is verified using a Lu-176 radiation source, and experimental result shows that the current generated from the H12700 position-sensitive photomultiplier tube (PSPMT) detector when the gamma radiation hits the scintillator crystal is successfully converted into voltage with the gain in agreement with our simulation result. Comparison of this GaN-based TIA with the reported silicon-based TIA shows superior performances for particle therapy imaging. The circuit is also tested under 100-MeV proton radiation with a fluence of 1.6 × 1011 c−2 and flux of 1.14 × 108 cm−2 s−1, and negligible variations in the linearity and gain in the postradiation measurements are observed. [ABSTRACT FROM AUTHOR]

Branches of physics and application technologies have widely utilized avalanche photodiodes (APDs) by coupling of scintillators with advantages of multiplication process and effective photosensitivity in a wide range of visible light wavelength. In addition, to meet the requirements for the purpose of each experiment, various types of APDs have been developed. The calibration system and characteristics of APD were constructed and studied by comparing several calibration methods. Electronics calibration is presented with charge injection and quantum efficiency (QE)-calibrated photodiode. By utilizing visible light-emitting diodes (LEDs) and with conventional electronic characteristics and a scintillation crystal with 22Na radioactive source, the APD gain was measured. Furthermore, the following were measured from the calibration method: QE, excess noise factor, and noise level. In this article, we compare our test results with one another, which are provided in the datasheet presented by the manufacturer, and discuss the possibility of standardizing the characterization of APDs by this calibration system. [ABSTRACT FROM AUTHOR]

This article describes a new concept of developing a composite plastic scintillator (PS) with better light out and detection efficiency of ionizing radiations by loading high Zeff radioluminescence (RL) phosphor powder. Gamma-ray interaction in PSs has been enhanced due to increased photoelectric absorption in the loaded BaFBr:Eu2+ phosphor powder. RL BaFBr:Eu2+ powder has been synthesized by a high-temperature solid-state diffusion method in reducing atmosphere. Polystyrene-based PS sheets of 250 ± 50 μm thickness have been prepared with 2.5-diphenyl oxazole (PPO) and 1.4-bis(5-phenyl-2-oxazolyl) benzene (POPOP) as primary and secondary fluors, respectively, mixed with the synthesized phosphor powder in different weight percentages. Radiation detection properties of the composite PS have been studied for alpha, beta, neutron, and gamma radiations of different energies. The composite PS sheet loaded with 20 wt% of phosphor powder showed maximum intensity for RL and photoluminescence (PL). Studies also confirmed a significant increase in the radiation detection efficiency in composite PS for various energies of beta and gamma rays. The lifetime measurement of the composite PS showed same nanosecond lifetime which is appropriate for fast counting and matches closely with the PS without loading. Pulse height analysis for various ionizing radiations of different energies confirmed significant improvement in the detection efficiency of loaded PSs. [ABSTRACT FROM AUTHOR]

The nuclear accident that occurred in Fukushima, Japan, in 2011, resulted in considerable radiation leaks and mass exposure owing to an insufficient initial response to the disaster. To prevent similar disasters in the future, their cause should be identified, analyzed, and addressed using radiation-monitoring systems. The core component of a radiation-monitoring system is the gamma camera. It consists mainly of a gamma detector and a collimator. We proposed a diverging collimator that incorporates a novel concept of a curved surface such that the collimator hole length is constant for all the incident hole angles. Therefore, the sensitivity is likely to be more uniform across the field of view (FOV) compared with the case of the conventional flat collimator. Through a simulation study, we determined the collimator parameters and compared the performance of the curved collimator with that of the conventional flat collimator. The results revealed the feasibility of achieving higher uniform sensitivity, up to 10.5% at the edge of the FOV by using the proposed curved collimator. The average peak-to-background ratio (PBR) of the curved collimator was determined to be higher by 10.8% across the entire FOV. This indicates that it produced a more distinct signal than the flat collimator. In our future research, we intend to fabricate a curved collimator and evaluate its performance experimentally. [ABSTRACT FROM AUTHOR]

In order to improve the image quality of a coded-aperture-based gamma-ray imaging apparatus, a method for removing Compton scattered and other multipixel events is presented that removes inaccurate position estimations from the data stream. In coded-aperture gamma-ray imaging detectors, scattering events that are shared between different partitions in the active medium can result in the inaccurate determination of the initial gamma-ray interaction position, the result of which is distortion in the angular reconstruction mapping. For coded-aperture system in which the rapid localization and identification of the emitting source is important, the distortion due to scattered radiation can increase the integration time of the system. We show, in both software and hardware implementations using a cerium-doped gadolinium aluminum gallium garnet pixelated scintillator array, that filtering the data to remove multipixel events can improve the image quality despite the efficiency loss associated with not utilizing all of the interactions within the detector. [ABSTRACT FROM AUTHOR]

The correct quantification of the dose released in charged particle therapy treatments requires the knowledge of the double differential fragmentation cross section of particles composing both the beam and the target. The FragmentatiOn Of Target (FOOT) experiment aims at measuring these cross sections for ions of interest for charged particle therapy applications. This article describes the performance of the time-of-flight (TOF)-wall detector of the experiment. The detector is composed of two layers of 44 cm $\times 2$ cm $\times 3$ mm plastic scintillator bars (20 for each layer), arranged orthogonally and read-out by silicon photomultipliers. The detector is designed to identify the charge of fragments ranging from protons to oxygen ions, with a maximum energy of 700 MeV/u, by measuring the energy released in the scintillators and the TOF with respect to a start counter. In this study, the detector was scanned with carbon ions of energy between 115 and 400 MeV/u and with a 60-MeV proton beam. The measurements show an energy resolution ($\sigma _{E}/\mu _{E}$) between 6% and 4% and a contribution of the detector to the TOF system time resolution between 25 and 20 ps (standard deviation) for carbon ions and between 100 and 80 ps for protons. [ABSTRACT FROM AUTHOR]

Lu2O3:Eu single crystals (SCs) and transparent ceramics (TCs) were prepared by the optical floating zone (OFZ) method and hot isostatic pressing (HIP) sintering method, respectively. Their photoluminescence (PL) and scintillation properties, including photoluminescence excitation (PLE) and PL, PL decay, X-ray excited luminescence (XEL) and afterglow level curves, were measured and compared. Their transmission spectra were also recorded. The differences of the PL and scintillation performance between the Lu2O3:Eu SC and TC have been studied. It is shown that the transmittance of the SC is higher than that of the TC, reaching as high as 80%. The Eu(S6) → Eu(C2) energy transfer states in the SC and TC are comparable through investigating the PL and PL decay curves. The main difference between the SC and TC in this work comes from the scintillation luminescence efficiency and afterglow level. The XEL intensity of the SC is 2.4 times that of the TC. The afterglow level of the TC is significantly higher than that of the SC, which probably results from the carrier traps formed in the forbidden gap related to the grain interface in ceramics sample. [ABSTRACT FROM AUTHOR]

Many radionuclide identification algorithms use statistical inference to collect a variety of features from gamma-ray spectra to deduce the presence of particular radionuclides. More modern algorithms require large amounts of data to learn and use latent features from spectra for classification. Both approaches are computationally expensive, which is reflected in their power consumption, and require large amounts of user intervention to prepare. In this article, we introduce a low-power, neuromorphic algorithm for the real-time identification of radionuclides which simultaneously considers the entire shape of a gamma-ray spectrum. Utilizing the output of a traditional gamma-ray detector, our spiking, locally competitive algorithm uses sparse coding optimization to compare global patterns in a gamma-ray spectrum with a dictionary of radionuclide templates. This approach allows us to model informative global features resulting from both photoelectric absorption and Compton scattering. For the purpose of radiation threat reduction, the dictionary consists of data from the Nuclear Wallet Cards, a list of radionuclides and their properties compiled by the National Nuclear Data Center. To test our algorithm, we use a variety of gamma-ray spectra created using radionuclides measured under laboratory conditions with varying durations, distances, activity levels, and backgrounds, resulting in a wide range of signal-to-noise ratios. We have created test sets for three different gamma-ray detector types, with 57Co, 137Cs, 152Eu, 60Co, 239Pu, and 235U sources, to quantify the effect of resolution, efficiency, and background on the accuracy of the algorithm. We demonstrate a true positive accuracy of 91% with a high-resolution detector and 89% with a low-resolution detector on the corresponding test sets. Experimenting with the same radionuclides included in the test sets in a variety of special nuclear material (SNM) masking configurations, we show that our algorithm is capable of correctly identifying both SNM and mask even when the activity level of the mask is several times higher than that of the SNM. We also determine that our algorithm achieves over a 99% reduction in power consumption over other radionuclide identification software applications, which is critical for long-term, independent monitoring and is the goal of this research. [ABSTRACT FROM AUTHOR]

Currently, we are developing a neutron scintillation detector prototype using silicon photomultipliers (SiPMs) as the photodetector. In order to reconstruct the position of single neutron events to an accuracy better than the pixel pitch of the SiPM, a very accurate photon count is required. Each pixel consists of 3200 microcells, operated in Geiger mode. A cell which is already triggered cannot detect any following photons hitting the cell, until it is recharged. This leads to a nonlinearity in the pixel’s response for a higher photon density impinging across the pixel. Previous studies provided a correction factor to estimate the saturation, by assuming a homogeneous photon distribution density and comparing it to the number of microcells. In our specific application, the photon distribution is not homogeneous, which is why we examined the influence of the homogeneity on the saturation. In this work, we present a case study for difference in nonlinearity effect for an inhomogeneous and homogeneous photon distribution density, given the light intensity is equal. The simulation results suggest that the effect could be higher for an inhomogeneous distribution. Therefore, care must be taken when using the established correction factor for saturation and an analysis of the photon distribution homogeneity is necessary. [ABSTRACT FROM AUTHOR]

The detection efficiency of a plastic scintillator (PLS) can be enhanced by loading with heavy metal nanoparticles to measure high-energy X-rays at a high count rate exceeding 10 7 s -1 using a fast scintillation detector. We successfully polymerized up to 60 wt% HfO 2 nanoparticle-loaded PLSs (Hf-PLSs) by mixing with polystyrene and 2-(4-tert-butylphenyl)5-(4-biphenyl)-1,3,4-oxadiazole as a fluorophore. Loading 40 wt% HfO 2 maintained a light yield of 79% of a commercially available 5 wt% lead-loaded PLS (EJ-256) with a much higher high-Z loading. We tested the 40 wt% Hf-PLS (8 mm in diameter, 3 mm in thickness) mounted on a photomultiplier tube using a synchrotron X-ray beam at beamline BL-14A of the photon factory (PF) ring. The detection efficiency of the X-ray detector reached 44.3 ± 0.2% at 50.0 keV. Counting rates of up to 2.76 × 10 7 s -1 were recorded at input photon rates of up to 3.74 × 10 8 s -1 in the multibunch mode of the PF ring. The pulse height and time spectra were observed using the 40 wt% Hf-PLS at 67.4 keV for application to synchrotron radiation nuclear resonant scattering on 61 Ni. The detection efficiency was 49.2 ± 0.2% at 67.4 keV, 7.2 times greater than that of EJ-256. A time resolution (full-width at half-maximum) of 0.32 ± 0.06 ns was obtained in the time spectrum but with a time resolution of 0.46 ns at best using EJ-256. The Hf-PLS is promising for applications in counting and timing measurements within the high-energy X-ray regions. [ABSTRACT FROM AUTHOR]