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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 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]

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]

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]

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]

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]

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]

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]

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]

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]