Neutron Scintillation Research Articles

Synergy of Organic and Inorganic Sites in 2D Perovskite for Fast Neutron and X‐Ray Imaging

AbstractFast neutron and X‐ray imaging are considered complementary nondestructive detection technologies. However, due to their opposite cross‐sections, development of a scintillator that is sensitive to both fast neutrons and X‐rays within a single‐material framework remains challenging. Herein, an organic–inorganic hybrid perovskite (C4H9NH3)2PbBr4 (BPB) is demonstrated as a scintillator that fully meets the requirements for both fast neutron and X‐ray detection. The hydrogen‐rich organic component acts as a fast neutron converter and produces detectable recoil protons. The heavy atom‐rich inorganic fraction efficiently deposits the energy of charged recoil protons and directly provides a large X‐ray cross‐section. Due to the synergy of these organic and inorganic components, the BPB scintillator exhibits high light yields (86% of the brightness of a commercial ZnS (Ag)/6LiF scintillator for fast neutrons; 22 000 photons per MeV for X‐rays) and fast response times (τdecay = 10.3 ns). More importantly, energy‐selective fast neutron and X‐ray imaging are also demonstrated, with high resolutions of ≈1 lp mm−1 for fast neutrons and 17.3 lp mm−1 for X‐rays; these are among the highest resolution levels for 2D perovskite scintillators. This study highlights the potential of 2D perovskite materials for use in combined fast neutron and X‐ray imaging applications.

Performance optimization of the scintillator neutron detectors for EMD in CSNS

Abstract Chinese Spallation Neutron Source (CSNS) has successfully produced its first neutron beam in 28th August 2017. It has been running steadily from March, 2018. According to the construction plan, the Engineering Materials diffractometer (EMD) will be installed between 2019- 2023. This instrument requires the neutron detectors with the cover area near 3m2 in two 90° neutron diffraction angle position, the neutron detect efficiency better than 40%@1Å, and the spatial resolution better than 4mm×200mm in horizontal and vertical directions respectively. We have developed an one-dimensional position sensitive neutron detector based on the oblique 6LiF/ZnS(Ag) scintillators, wavelength shifting fibers and SiPMs (Silicon Photomultipliers) readout. The inhomogeneity of the neutron detection efficiency between each pixel and each detector module, which caused by the inconsistency of the wave-length shifting fibers in collecting scintillation photons, need to be mitigated before the installation. A performance optimization experiment of the detector modules was carried out on the BL20 (Beam Line 20) of CSNS. Using water sample, the neutron beam with Φ5mm exit hole was dispersed relate evenly into the forward space. According to the neutron counts of each pixel of the detector module, the readout electronics threshold of each pixel is adjusted. Compared with the unadjusted detector module, the inhomogeneity of the detection efficiency for the adjusted one is improved from 69% to 90%. The test result of the diffraction peak of the standard sample Si showed that the adjusted detector module works well.

Determination of energy-dependent neutron backgrounds using shadow bars

Understanding the neutron background is essential for determining the neutron yield from nuclear reactions. The neutron backgrounds were determined for heavy-ion collision experiment using the shadow-bar method, where beams of 40,48Ca at 56, 140 MeV/u impinged on targets of 58,64Ni and 112,124Sn. In the analysis presented here, brass shadow bars are placed in front of organic liquid scintillator neutron detectors to determine the energy-dependent neutron background fractions. The measurement of neutron spectra with and without shadow bars is important to determine the neutron background more accurately. The neutron background, along with its sources and systematic uncertainties, are explored with a focus on the impact of background models and their dependence on neutron energy.

Large scale BN-perovskite Nanocomposite Aerogel Scintillator for Thermal Neutron Detection.

State-of-the-art thermal neutron scintillation detectors rely on rare isotopes for neutron capture, lack stability and scalability of solid-state scintillation devices, and poorly discriminate between the neutron and gamma rays. Our boron nitride (BN) - CsPbBr3 perovskite nanocomposite aerogel scintillator enables discriminative detection of thermal neutrons, features the largest known size (9cm across), the lowest density (0.17g/cm3 ) among the existing scintillation materials, high BN (50%) perovskite (1%) contents, high optical transparency (85%), and excellent radiation stability. The new detection mechanism relies on thermal neutron capture by 10 B and effective energy transfer from the charged particles to visible-range scintillation photons between the densely packed BN and CsPbBr3 nanocrystals. Low density minimizes the gamma ray response. The neutrons and gamma rays are discriminated by complete decoupling of the respective single pulses in time and intensity. These outcomes open new avenues for neutron detection in resource exploration, clean energy, environmental, aerospace, and homeland security applications. This article is protected by copyright. All rights reserved.

Novel flexible and conformable composite neutron scintillator based on fully enriched lithium tetraborate

Thermal neutron detection is a key subject for nuclear physics research and also in a wide variety of applications from homeland security to nuclear medicine. In this work, it is proposed a novel flexible and conformable composite thermal neutron scintillator based on a fully enriched Lithium Tetraborate preparation (^{6}Li_2^{10}B_4O_7) combined with a phosphorescent inorganic scintillator powder (ZnS:Ag), and is then distributed into a polydimethylsiloxane matrix. The proposed scintillator shows a good neutron detection efficiency (max. sim 57% with respect to the commercial EJ-420), an average light output of sim 9000 ph/neutron-capture, a remarkable insensitivity to gamma-rays (Gamma Rejection Ratio <10^{-11}), and an extraordinary flexibility, so as to reach extremely small curvature radii, down to 1.5 mm, with no signs of cracking or tearing. Its characteristics make it suitable to be employed in scenarios where non-standard geometries are needed, for example, to optimize the detector performance and/or maximize the detection efficiency. Finally, the response of a hybrid detector made of a plastic scintillator, wrapped with the proposed scintillator, coupled to a silicon photomultiplier array is described, and the excellent discrimination between gamma-rays, fast and thermal neutrons resulting from data processing is demonstrated.

Growth of Eu doped LiBr/BaBr2 eutectic and its thermal neutron response

In this study, Eu:6LiBr/BaBr2 with a high Li concentration was developed as a novel neutron scintillator. Here, an Eu-doped BaBr2 phase acted as a scintillator and 6Li-containing LiBr phase acted as a neutron capturer. Eu:6LiBr/BaBr2 eutectics were fabricated via the vertical Bridgman technique in quartz ampoules. The scintillation performance of Ce:6LiBr/LaBr3 was measured using electron and neutron irradiation to evaluate its potential as a neutron scintillator. The grown Eu:6LiBr/BaBr2 eutectic exhibited a lamellar eutectic structure and optical transparency as well as a 410 nm emission due to the Eu2+ 5d–4f transition. The light yield under thermal neutron excitation was estimated to be 5600 photons/neutrons. The scintillation decay time was 550 ns.

Neutron-gamma events discrimination under complex circumstances using ResNet

On scintillator detectors, neutron and gamma rays could generate signals. These signals are generated internally and cannot be shielded, and there are various complex circumstances during data collection, such as piled-up pulse at high count rates and overflowed pulse caused by detector range limits. It is challenging to screen these complex circumstances using conventional methods like charge comparison. Conventional methods have low accuracy and lack self adaptability, to address these problem, a neural network based on residual connection structure (ResNet) was proposed. On the basis of the collected real signal, the pulse waveforms under complex circumstances were simulated. After integrating these waveforms into a dataset, they were trained and validated by ResNet and compared with two neural network algorithms MLP and CNN. The false predictions number of ResNet is 60% and 73% lower than that of CNN and MLP. The macro average F1 score of ResNet was 0.9956, which was significantly higher than 0.9885 of CNN and 0.9855 of MLP. And in the ROC and AUC, ResNet is still the best performing method, furthermore the improvement of ResNet to CNN is higher than that of CNN to MLP. These results indicated that Proposed ResNet is more suitable for neutron-gamma events discrimination in complex situations.

Ten springs of experiments in CROCUS

Around a decade ago, a new team rebuilt experimental research at EPFL’s nuclear facilities, and in particular in the CROCUS nuclear reactor. After a broad investigation and open discussions with colleagues from the nuclear community, a number of experiments and research directions were selected. They range from reactor physics to nuclear data, with a focus on instrumentation. We present here the variety of experiments carried out and how instrumentation has been instrumental in these perspectives. Developments on branching or intrinsic reactor noise were made possible thanks to extensive theoretical investigation coupled with the developments of pulse and current modes neutron detection systems, as well as the LEAF gamma detection array. With regard to modulation or perturbation reactor noise, a study of fuel rods vibration was carried out thanks to the unique COLIBRI in-core fuel rods oscillation device; in the VOID experiments, a method was tested to measure the void coefficient with neutron modulation; in the APRHODITE project, the PISTIL rotating absorber, or absorber of variable strength, was used to determine the zero power reactor transfer function, in order to obtain feedback on kinetics nuclear data, particularly delayed neutrons. On the topic of nuclear data, the PETALE programme consisted on criticality and transmission experiments for the study of stainless steel, using instrumented metal reflectors. New dosimetry methodologies were developed for consistent and complete propagation of uncertainties, which also enabled experiments to be optimized. It will be continued in the HARVEST-X project, and its pile-oscillation program, BLOOM. Last but not least, developments in dosimetry as well as for a novel miniature neutron scintillation technology (MiMi detectors) allowed for interand intrapin (NECTAR) neutron measurements. 160 MiMi detectors have recently been distributed throughout the CROCUS core in a unique 3D detector array called SAFFRON, paving the way for novel high-resolution neutronics.

Study of a possible silicon photomultiplier based readout of the large plastic scintillator neutron detector NeuLAND

The NeuLAND (New Large-Area Neutron Detector) plastic-scintillator-based time-of-flight detector for 0.1–1.6GeV neutrons is currently under construction at the Facility for Antiproton and Ion Research (FAIR), Darmstadt, Germany. In its final configuration, NeuLAND will consist of 3,000 2.7m × 5 cm × 5 cm big plastic scintillator bars that are read out on each end by fast timing photomultipliers.Here, data from a comprehensive study of an alternative light readout scheme using silicon photomultipliers (SiPM) are reported. For this purpose, a NeuLAND bar was instrumented on each end with a SiPM-based prototype of the same geometry as a 1” photomultiplier tube, including four 6 × 6mm2 SiPMs, amplifiers, high voltage supply, and microcontroller.Tests were carried out using the 35MeV electron beam from the superconducting Electron Linac for beams with high Brilliance and low Emittance (ELBE) with its picosecond-level time jitter in two different modes of operation, namely parasitic mode with one electron per bunch and single-user mode with 1–60 electrons per bunch. Acqiris fast digitisers were used for data acquisition. In addition, off-beam tests using cosmic rays and the NeuLAND data acquisition scheme have been carried out.Typical time resolutions of σ≤ 120ps were found for ≥95% efficiency for minimum ionising particles, improving on previous work at ELBE and exceeding the NeuLAND timing goal of σ< 150ps. Over a range of 10–300MeV deposited energy in the NeuLAND bar, the gain was found to deviate by ≤10% (≤20%) from linearity for 35μm (75μm) SiPM pitch, respectively, satisfactory for calorimetric use of the full NeuLAND detector. The dark rate of the prototype studied was found to be lower than the expected cosmic-ray induced background in NeuLAND.

Thermal neutron scintillation improvement in Ce:Li6Y(BO3)3 single crystals by thermal treatment

The development of efficient, low-cost, and stable solid-state materials for portable thermal neutron detection is highly expected in order to substitute the currently used 3He and BF3 tank detectors. A few Li-based glasses and halide compounds have emerged as candidates, however, all of them present critical drawbacks for their practical implementations. Ce:Li6Y(BO3)3 is a priori a very promising oxide candidate that however has been disregarded so far due to its negligibly low light yield, caused by a poor crystalline and optical quality. In this study, we demonstrate that a post-growth thermal treatment is the key parameter to drastically reduce the concentration of intrinsic defects and scattering centers that lead to severe non-radiative recombination of excited electrons. Even though this annealing step also involves the oxidation of activator Ce3+ ions to Ce4+, a drastic enhancement of the light yield by ∼600% is achieved independently of the Ce3+ concentration within the considered range. The obtained light yield of 4650 ph n−1 is already close to that of reference Li-glass (commercial GS20 with 6000 ph n−1). An additional improvement can be envisaged upon further optimization of the Ce3+ concentration and the annealing time, so that Ce:Li6Y(BO3)3 reaches a light yield comparable to the state-of-the-art one for thermal neutron detection.

Titanium-doped LiAlO2 ceramics for neutron scintillation

A series of bulk ceramic samples of titanium-doped LiAlO2 with doping concentrations of 0.05, 0.1, 0.5 and 1.0 at% were prepared using a sol-gel method. The LiAlO2:Ti samples showed emission in two spectral regions around 380 and 765 nm associated with the CT transition of Ti4+ and the d-d transition of Fe3+ impurities, respectively. The sample composition with 0.5 at% doping concentration exhibited the highest emission intensity. Furthermore, dense ceramic samples with 0.5 at% Ti-doping were prepared using spark plasma sintering. These samples exhibited intense CT luminescence of Ti4+ at 380 nm with a decay time of approximately 2.3 μs, while the emission of Fe3+ impurities was mostly suppressed.

Performance test of different silicon photomultipliers for the 6LiF:ZnS(Ag) based neutron detectors of CSNS

The China Spallation Neutron Source (CSNS) is a large scientific facility whose main aim is to support multidisciplinary research on material characterization using neutron scattering. Twenty neutron spectrometers will be built as multidisciplinary platforms for scientific research by national institutions, universities, and industry. Scintillator neutron detectors for the spectrometers under construction have recently been developed using silicon photomultipliers (SiPMs) for the readout. This paper studies the characteristics of three candidate SiPMs, including the breakdown voltage, gain, temperature coefficient, dark count rate, and radiation tolerance. Two measurement platforms were built to evaluate each SiPM. We summarize the results from our analysis of laboratory tests and beam test data to characterize the performance of the SiPMs. The MicroFJ-30035-TSV SiPM manufactured by the SensL Corporation is chosen as the best SiPM for the scintillator detectors at CSNS.

Development of fluoride materials for neutron detection

We have studied various lithium containing fluoride materials as neutron scintillators for the last 15 years. Fluoride scintillator samples were prepared by melt growth techniques and their scintillation properties were investigated under thermal neutron irradiation. Developed fluoride scintillators show non-hygroscopicities and full-absorption peaks in the pulse height spectra under thermal neutron irradiation. The highest light yield among the samples was approximately 40000 photons/neutron. Several fluoride materials can be used as a non-hygroscopic neutron scintillators.

Исследование и подавление чувствительности нейтронных сцинтилляционных детекторов к гамма-излучению

The article continues the consideration of the main problems arising in the development of a real-time multi-detector neutron spectrometer. In previous articles [1,2], possible ways of forming the spectral characteristics of polystyrene scintillation neutron detectors and the results of their calculation using the GEANT-4 modeling software library [1] and restoring the absolute values of the spectral components of the measured neutron flux from their normalized values determined with using a pretrained neural network based on the responses of detectors used in the spectrometer with different spectral characteristics [2]. This article presents the results of studying the processes of scintillation initiation in organic scintillators under the influence of neutron and gamma radiation and considers possible methods for suppressing the sensitivity of a multi-detector neutron spectrometer to accompanying gamma radiation.

Digital pulse analysis for fast neutron recoil spectroscopy with a 4He scintillation detector

Helium-4-based fast neutron scintillation detectors are an attractive alternative to pulse-shape discrimination-capable organic scintillators for fast neutron detection and spectroscopy, as the response of the detectors to gamma rays is intrinsically limited to low energy deposition. Consequently, the neutron recoil distribution can be measured with these detectors without the need for pulse shape analysis. In this work, the response of an Arktis S670 4He scintillation detector to D-D, D-T, and 252Cf neutrons was measured. The detector has a unique construction and readout mechanism, with multiple output channels observing the same scintillation event, and an analysis method was developed to aggregate the outputs from all channels into a single list. The D-D and D-T neutron responses were used to perform a two-point energy calibration, which yielded a near-zero intercept, suggesting that the 4He scintillation medium behaves linearly to a higher energy than previously reported, and that a two-point calibration is sufficient for nuclear recoil energies below 9 MeV. Furthermore, the detector was measured to have 16.7-ns FWHM time resolution when using the developed custom analysis, a reduction of 4.9 ns when compared to the conventional pulse analysis.

Numerical studies on saturated kink and sawtooth induced fast ion transport in JET ITER-like plasmas

This presentation examines the energetic particle transport induced by saturated kink modes and sawtooth crashes in JET deuterium plasmas. It is known that kink mode-resonant transport and phase-space redistribution from sawtooth crashes can drive strong fast ion transport with dependencies on particle pitch and energy. Measurements with JET’s Faraday cup fast ion loss detector array have shown that the internal kink growth phase preceding sawtooth crashes produces substantial fast ion losses. This report will numerically investigate the dominant energetic particle transport mechanism with a detailed examination of the fast ion phase-space dependencies, resonances, orbit topology changes, induced losses, and redistribution associated with the long-lived, resonant, kink mode and non-resonant sawtooth crash. The ORBIT-kick model forms the basis of the transport studies with realistic fast ion distributions produced from TRANSP. A recently created reduced model for sawtooth induced transport is used while the saturated kink modes are modeled with ideal magnetohydrodynamic codes. The simulations were further validated against experiment with a newly developed synthetic Faraday cup fast ion loss detector in addition to scintillator probe and neutron measurements.

Transparent Microcomposite Films Based on a Ce-Doped Li6Gd(BO3)3 Scintillator for Radiation Detection.

Scintillators are widely used for high-energy radiation detection. Hybrid inorganic–organic composite scintillators with high light yields, high light decay rates, excellent stability, and low costs are in great demand. Here, we report a novel scintillator composed of Ce-doped Li6Gd(BO3)3 (LGBO) microphosphors (MPs) and polymethyl methacrylate for X-ray and thermal neutron detection. The Ce-doped LGBO MPs, fabricated using a facile high-temperature solid-state reaction method, exhibit intense blue light at 416 nm under X-ray and UV excitation and have a high photoluminescence quantum yield of ∼63%. More importantly, the composite scintillator based on these MPs has excellent transparency and luminescence intensity. The luminescence integral intensity of composite scintillators is superior to that of commercial CsI:Na under X-ray excitation, and the light yield under thermal neutron irradiation is 21,000 photons/thermal neutron. The scintillation decay time is found to be below 600 ns. The neutron−gamma signal discrimination and neutron detection efficiency of the composite scintillators are acceptable for practical application. There is an excellent separation between neutron and background events. It represents significant improvements in scintillator performances, especially for reliable thermal neutron scintillators that are likely to improve the data qualities of scientific instruments, including charge-coupled device-based imagers and Anger logic-based position-sensitive detectors in neutron user facilities.

Neutron transmission imaging with a portable D-T neutron generator

A portable fast-neutron imaging system is being developed to provide complementary information to field X-ray imaging. Applications include inspection of vehicles and infrastructure for corrosion, measurement of material levels in containers, and inspection of munitions and suspicious packages. While fast-neuron imaging generally provides lower imaging resolution compared to X-rays, fast-neutron interaction cross-sections have a weak dependence on material Z. This enables imaging of low-Z materials inside high-Z materials. Here, we discuss the limitations and current improvements in fast-neuron imaging. Limitations in portable fast-neutron imaging systems include low D-T neutron generator output, low light production in ZnS(Cu) imaging scintillators, low resolution due to scintillator thickness and D-T spot size, and digital-panel darknoise that varies in time and position and that can be 100× larger than the neutron signal. We have made improvements in these areas through development of a segmented high light yield scintillator, panel noise mitigation techniques, and testing of new high-output, small spot size D-T neutron generators. The segmented high light yield fast-neutron scintillator demonstrated 5× increase in light compared to ZnS(Cu). An additional 2× improvement in signal-to-noise was demonstrated with panel-noise mitigation techniques. Our MCNP calculations also show good agreement with neutron imaging results We have demonstrated improvements in fast-neutron imaging through development of a segmented high light yield neutron scintillator, mitigation of digital panel noise, and preliminary testing with new high-output, small spot size D-T neutron generators. We have also demonstrated good results modeling fast-neutron images and scatter effects using MCNP.

Growth of 6Li-enriched LiCl/BaCl2 eutectic as a novel neutron scintillator

In this study, Eu:6LiCl/BaCl2 with a high Li concentration was developed as a novel thermal neutron scintillator. Eu ions were doped as activators for the BaCl2 phase, and Eu:6LiCl/BaCl2 eutectics were grown via the vertical Bridgman–Stockbarger method in quartz ampoules (inner diameter = 4 mm). The Eu:6LiCl/BaCl2 eutectic exhibited a lamellar eutectic structure and optical transparency. The 400 nm emission due to the Eu2+ 4f–5d transition was observed in the BaCl2 phase by a cathode luminescence measurement. The light yield under neutrons was estimated to be over 20 200 photons MeV−1. A PSD study was also performed using gamma and alpha-rays. The Eu:6LiCl/BaCl2 eutectic scintillator showed good potential for PSD.

Growth and scintillation properties of LiBr/CeBr3 eutectic scintillator for neutron detection

A 6LiBr/CeBr3 eutectic thermal-neutron scintillator, with a high 6Li concentration, was developed using the vertical Bridgman method. The grown eutectic contained an 6Li molar ratio of 35%, which is higher than those of the commercial neutron scintillators such as Ce:LiCaAlF6 and Ce:Cs2LiYCl6. Furthermore, it showed optical transparency and a lamellar eutectic structure elongating along the growth direction. The synthesized eutectic showed emission peaks at 360 and 380 nm, originating from the Ce3+ 5d-4f transition in the CeBr3 scintillation phase. The scintillation performance of 6LiBr/CeBr3 was evaluated under X-ray, γ-ray, and neutron irradiation to corroborate its neutron detection potential.