High Neutron Detection Efficiency Research Articles

Search for a Neutron Dark Decay in ^{6}He.

Neutron dark decays have been suggested as a solution to the discrepancy between bottle and beam experiments, providing a dark matter candidate that can be searched for in halo nuclei. The free neutron in the final state following the decay of ^{6}He into ^{4}He+n+χ provides an exceptionally clean detection signature when combined with a high efficiency neutron detector. Using a high-intensity ^{6}He^{+} beam at Grand Accélérateur National d'Ions Lourds, a search for a coincident neutron signal resulted in an upper limit on a dark decay branching ratio of Br_{χ}≤4.0×10^{-10} (95% C.L.). Using the dark neutron decay model proposed originally by Fornal and Grinstein, we translate this into an upper bound on a dark neutron branching ratio of O(10^{-5}), improving over global constraints by one to several orders of magnitude depending on m_{χ}.

Feasibility of neutron coincidence counting for spent TRISO fuel

High-temperature gas reactors rely on TRIstructural-ISOtropic (TRISO) fuel for enhanced fission product retention. Accurate fuel characterization would improve monitoring of efficient fuel usage and accountability. We developed a new neutron multiplicity counter (NMC) based on boron coated straw (BCS) detectors and used it in coincidence mode for 235U assay in TRISO fuel. In this work, we demonstrate that a high-efficiency version of the NMC encompassing 396 straws is able to estimate the 235U in used TRISO-fueled pebbles or compacts with a relative uncertainty below 2.5% in 100s. We performed neutronics and fuel depletion calculation of the HTR-10 pebble bed reactor to estimate the neutron and gamma-ray source strengths of used TRISO-fueled pebbles with burnup between 9 and 90GWd/t. Then, we measured a gamma-ray intrinsic efficiency of 10−12 at an exposure rate of 340.87R/h. The low gamma-ray sensitivity and high neutron detection efficiency enable the inspection of used fuel.

Experimental study of spatial resolution of MCPs for compact high-resolution neutron radiography system

Neutron-sensitive microchannel plates (MCPs) have been widely used as detectors in neutron radiography systems due to their high neutron detection efficiency and superior spatial resolution. These MCPs are typically employed in large-scale facilities with high neutron flux and large L/D ratios, allowing them to achieve excellent spatial resolution. However, it was uncertain whether the MCPs’ high-resolution advantage could be fully utilized in compact radiography systems with limited neutron yield and lower L/D ratios. To investigate this, thermal neutron imaging experiments were conducted in this paper. The results showed that MCPs can offer a 0.25 mm spatial resolution, compared to the 0.3 mm of a 6LiF/ZnS detector. Additionally, a centroid algorithm imaging technique was utilized to further enhance the MCPs’ spatial resolution up to 0.2 mm. This research on MCPs can also be used as a reference for other neutron radiography systems with limited L/D ratios.

3D Microstructured Inorganic Perovskite Materials for Thermal Neutron Detection

AbstractA combination of novel techniques such as a solvent‐free thin‐film deposition, perovskite patterning, and 10B back‐fill technique enables the high neutron detection efficiency in a perovskite‐based microstructured thermal neutron detector. High‐efficiency cesium lead bromide (CsPbBr3) perovskite‐based microstructured detectors are demonstrated here. Trenches up to 10 µm deep are etched into the CsPbBr3 thin films using a novel dry etching process involving a combination of HBr and Ar plasma. The microstructured diodes are then backfilled with isotopically enriched boron as neutron conversion material via a sedimentation process to preserve the perovskite integrity. The fabricated microstructured CsPbBr3 thermal neutron detectors show an efficiency of 4.3%. This represents >1.2x efficiency improvement over planar silicon (3.5%) and >2x efficiency improvement over planar CsPbBr3 (2.1%) detectors, respectively. More importantly, gamma‐ray discrimination of 107 is measured in CsPbBr3‐based microstructured neutron detectors.

Neutron detection efficiency of the Neutron dEtector with Xn Tracking (NEXT)

An efficient neutron detection system with good energy resolution is required to correctly characterize decays of neutron-rich nuclei where β-delayed neutron emission is a dominant decay mode. The Neutron dEtector with Xn Tracking (NEXT) has been designed to measure β-delayed neutron emitters. By segmenting the detector along the neutron flight path, NEXT reduces the associated uncertainties in neutron time-of-flight measurements, improving energy resolution while maintaining detection efficiency. Detector prototypes are comprised of optically separated segments of a neutron-gamma discriminating plastic scintillator coupled to position-sensitive photomultiplier tubes. The first performance studies of this detector showed that high intrinsic neutron detection efficiency could be achieved while retaining good energy resolution. The results from the efficiency measurements using neutrons from direct reactions are presented.

Gd-containing scintillators for thermal neutron detection via graph-based particle discrimination.

Neutron-gamma discrimination (NGD) for gadolinium-containing scintillators is a challenging issue which prevents them from being used in highly efficient neutron detectors with high signal-to-noise ratios. Pulse-shape based digital-signal processing has been selected to tackle this issue, with an emphasis on the dimensionality reduction of the raw data and capability to mitigate the influence of noise, unwanted variations, and outliers on the accuracy of classification. We present two graph-embedded non-negative matrix factorization digital classifiers in which an event graph (or a network) is introduced to find a low-dimensional structure hidden in the high-dimensional experimental data. Utilizing energy-independent normalized features of waveforms and a graph composed of mixed-source reference events, the smooth or sparse low-dimensional representation of detector signals from a Ce:Gd3Al2Ga3O12 scintillator leads to a high thermal neutron detection efficiency (77%-80%) and a high NGD ratio (neutron-gamma efficiency ratio, ∼109) simultaneously. Moreover, excellent discrimination between neutron and ambient background events has been achieved. The proposed graph-embedded algorithms may be applied not only for thermal-neutron position-sensitive detectors and single-channel detectors but also for other radiation detectors that need excellent particle (or crystal) discrimination capabilities and high detection efficiencies in many applications, including medical imaging, nondestructive testing, and security scans.

Ion assisted near-complete filling of high aspect ratio trenches for 3-D neutron detectors

A single-step process has been developed for the conformal deposition of boron carbide in high aspect ratio trenches fabricated in an n-type (111) silicon substrate. Plasma enhanced chemical vapor deposition was used to deposit boron carbide from ortho-carborane (OC2B10H12) precursor mixed with helium and argon gas. The depositions were carried out under substrate self-bias conditions to achieve a high fill factor using forward-directed ions. Nearly complete filling of 25 µm deep trenches with high-aspect ratio (> 6:1) via conformal coating of side walls has been confirmed from cross-sectional scanning electron microscopy studies. The results presented in this article establish that the process technology developed for achieving conformal deposition of the neutron stopping layer is suitable for the fabrication of Silicon p-i-n based three-dimensional thermal neutron detectors with high neutron detection efficiency.

Simulation and optimization of the boron-lined MWPC neutron detectors

Boron-lined gas detectors are prospective alternatives to helium-3-based neutron detectors. For boron-lined multi-wire proportional chamber (MWPC) with neutron grazing incident angle geometry, high neutron detection efficiency and 3D position sensitive can be realized. In this paper, a multi-layer boron-lined MWPC was studied. Influences of the boron coating thickness, coating layer numbers and neutron incident angle on the neutron detection efficiency were studied and optimized with Geant4 simulation. The output signal properties including induced signal width on the readout plane, the time resolution and gas gain uniformity of the detector were studied with Garfield program. The results show that the neutron detection efficiency can be significantly increased by using neutron grazing incident geometry. For 4 layers of 10B4C with thickness of 1 µm, the neutron detection efficiency can reach to 54.56%, 49.17% and 44.36% when neutron incident angle is 6°, 8° and 10°, respectively. For detector with curved geometry, the gas gain is nonuniform among the anode wires, and using separate high voltage for each anode wire or wires group can effectively reduce the nonuniform of the gas gain. The results of this work can be used to optimize the detector design.

Performance Assessment of Amplification and Discrimination Electronic Devices for Passive Neutron Measurements

The assessment of fissile material mass is a key requirement to enhance radioactive waste management and to ensure a high level of safety in the nuclear industry. The assessment of plutonium fissile mass by passive coincidence measurements is usually obtained by detecting the neutrons generated by the spontaneous fissions of Pu isotopes. The detection and the quantification of a fissile mass in the radioactive waste can also be carried out using active neutron interrogation with a pulsed D-T neutron generator. The 14-MeV neutrons are moderated to induce fissions in the uranium and plutonium-contaminated waste. The emitted neutron signal can be analyzed by considering their detection time after the generator pulse. Data are measured according to the principles of the neutron measurement techniques. As proportional counters filled with 3He gas display high neutron detection efficiency and good gamma-ray immunity, they are the reference detector for passive neutron coincidence counting. A charge preamplifier or a current amplifier, depending on applications, collects the electric pulse produced by neutron interaction in the 3He gas, and a threshold discriminator produces a logic pulse used for neutron counting. This article describes the performance assessment of different commercially-available electronics from Mirion Technologies, Precision Data Technology (PDT), Mesytec, as well as MONACO electronics originally developed by CEA LIST for fission chamber measurements in experimental reactors. Comparative passive neutron measurements are carried out with these electronics at CEA/DEN Nuclear Measurement Laboratory in Cadarache. Overall, PDT and Mesytec electronics show similar detection efficiency as the ACH-NA98 charge amplifier, which is commonly used in our laboratory for such applications. However, MONACO electronics have a lower detection efficiency, similar to the Mirion 7820 current amplifier used in specific high-count rate applications. An optimization of MONACO settings would probably be necessary to adapt to 3He counters instead of fission chambers.

Performance assessment of amplification and discrimination electronic devices for passive neutron measurements

The knowledge of the fissile material mass is a key challenge to enhance radioactive waste management and to ensure a high level of safety in nuclear industry. Data is analyzed according to the principles of the neutron measurement techniques. As proportional counters filled with 3He gas display high neutron detection efficiency and a good gamma-ray discrimination, they are the reference detector for passive neutron coincidence counting. A charge preamplifier or a current amplifier, depending on applications, collects the electric pulse produced by neutron interaction in the 3He gas and a threshold discriminator produces a logic pulse used for neutron counting. This paper describes the performance assessment of different commercially available electronics from Mirion Technologies, Precision Data Technology (PDT), Mesytec, as well as MONACO electronics originally developed by CEA LIST for fission chamber measurements in experimental reactors. Comparative passive neutron measurements are carried out with these electronics at CEA/DEN Nuclear Measurement Laboratory in Cadarache. Overall, PDT and Mesytec electronics show similar detection efficiency as the ACH-NA98 charge amplifier, which is commonly used in our laboratory for such applications. However, MONACO electronics have a lower detection efficiency, similar to Mirion 7820 current amplifier used in specific high-count rate applications. An optimisation of MONACO settings would probably be necessary to adapt to 3He counters instead of fission chambers.

Use of Neutron Scintillation Detectors as a Substitute for Helium-3 Counters in Radiation Monitors

The purpose of this work is to analyze the use of detecting materials in radiation monitors as well as the replacement of widely used 3H-based neutron counters by neutron-detection scintillation technology. The replacement of helium counters is a consequence of two factors: the lack of 3He and widespread use of 3He-based counters in safety equipment, such as volumetric neutron detectors. Selection criteria for evaluating promising technologies are used in this work, specifically, high absolute neutron detection efficiency – efficiency at least 1.5 counts in 1 sec in detecting 1 ng 252Cf at distance of 2 m in a 20 mm thick moderator and low sensitivity to γ-ray detection – γ-ray detection efficiency not exceeding 10–6 with irradiation by a 0.1 μSv/h γ-ray source. Since they can have a large sensitive area and high resolution, scintillation detectors are now being proposed as alternatives to helium counters. But it is necessary to find an optimal scintillator possessing simultaneously low sensitivity to γ-radiation and to choose an optimal method of measuring information. Promising neutron detection technologies based on the glasses Li2OSiO2:Ce3+, LiF/ZnS(Ag+), Li6Gd(BO3)3:Ce, Cs2LiYCl6(Ce) (CLYC) as well as EJ-254 boron-doped plastic are examined from the standpoint of the posed problems.

Conceptual design and first results for a neutron detector with interaction localization capabilities

A new high-precision detector for studying neutrons from beta-delayed neutron emission and direct reaction studies is proposed. The Neutron dEtector with Xn Tracking (NEXT) array is designed to maintain high intrinsic neutron detection efficiency while reducing uncertainties in neutron energy measurements. A single NEXT module is composed of thin segments of plastic scintillator, each optically separated, capable of neutron-gamma discrimination. Each segmented module is coupled to position sensitive photodetectors enabling the high-precision determination of neutron time of arrival and interaction position within the active volume. A design study has been conducted based on simulations and experimental tests leading to the construction of prototype units. First results from measurements using a $^{252}$Cf neutron source and accelerator-produced monoenergetic neutrons are presented.

Fast-Neutron Detectors Based on Surface-Barrier GaAs Sensors with an Ultrahigh-Molecular-Weight Polyethylene Converter

Surface-barrier structures based on high-purity epitaxial GaAs layers with an ultrahigh-molecular-weight polyethylene converter were tested as fast-neutron detectors. The α-particle spectra and the response to fast neutrons were measured under exposure to a 241Am−Be source. The detectors demonstrated a high neutron-detection efficiency (1.22 × 10−3 counts/neutron) and an acceptable ratio of the signal to γ‑ray background (approximately 40). The possibility of using such detectors at temperatures as high as 120°C was shown.

Large High-Efficiency Thermal Neutron Detectors Based on the Micromegas Technology

Due to the so-called 3He shortage crisis, many detection techniques for thermal neutrons are currently based on alternative converters. There are several possible ways of increasing the detection efficiency for thermal neutrons using the solid neutron-to-charge converters 10B or 10B4C. Here, we present an investigation of the Micromegas technology. The micro-pattern gaseous detector Micromegas was developed in the past years at Saclay and is now used in a wide variety of neutron experiments due to its combination of high accuracy, high rate capability, excellent timing properties, and robustness. A large high-efficiency Micromegas-based neutron detector is proposed for thermal neutron detection, containing several layers of 10B4C coatings that are mounted inside the gas volume. The principle and the fabrication of a single detector unit prototype with overall dimension of ~15 × 15 cm2 and its possibility to modify the number of 10B4C neutron converter layers are described. We also report results from measurements that are verified by simulations, demonstrating that typically five 10B4C layers of 1–2 μm thickness would lead to a detection efficiency of 20% for thermal neutrons and a spatial resolution of sub-mm. The high potential of this novel technique is given by the design being easily adapted to large sizes by constructing a mosaic of several such detector units, resulting in a large area coverage and high detection efficiencies. An alternative way of achieving this is to use a multi-layered Micromegas that is equipped with two-side 10B4C-coated gas electron multiplier (GEM)-type meshes, resulting in a robust and large surface detector. Another innovative and very promising concept for cost-effective, high-efficiency, large-scale neutron detectors is by stacking 10B4C-coated microbulk Micromegas. A prototype was designed and built, and the tests so far look very encouraging.

Computational investigation of arranged scintillating particle composites for fast neutron detection

Composite materials have the potential to play an important role in enabling high-performance and cost-effective neutron detectors for fundamental science, global security, and dosimetry applications. This study presents neutron and gamma transport simulation results on composites consisting of 6Li-containing GS20 scintillator glass particles arranged in an organic matrix. These composites achieve high sensitivity for neutrons while suppressing signals from gamma rays. The simulations successfully identified optimal composite parameters such as particle size, geometry, and inter-particle pitch. This information is key to the subsequent fabrication and scale-up of the desired GS20-in-acrylic composite. The simulation results presented in this paper demonstrate that arranged composites can provide high neutron detection efficiency with gamma misidentification values of <1 in 106 gamma rays, assuming irradiation with a 252Cf spontaneous fission source.

Study of n/γ discrimination using 3He proportional chamber in high gamma-ray fields

The 3He proportional chamber is widely used for neutron measurement owing to its high neutron detection efficiency and simplicity for gamma-ray rejection. In general, the neutron and gamma-ray signals obtained from the 3He proportional chamber can be easily separated by the difference in the pulse heights. However, for a high gamma-ray field, the gamma-ray signal cannot be precisely eliminated by the pulse height due to gamma-ray pulse pileup which causes the pulse height of gamma-ray pulse to increase and making the pulses due to neutrons and gamma rays indistinguishable. In this study, an improved algorithm for n/γ discrimination using a parameter, which is the ratio of the rise time to the pulse height, is proposed. The n/γ discrimination performance of the algorithm is evaluated by applying it to 252Cf neutron signal separation from various gamma-ray exposure rate levels ranging 0.1–5 R/h. The performance is compared to that of the conventional pulse-height analysis method in terms of the gamma elimination ratio. The suggested algorithm shows better performance than the conventional one by 1.7% (at 0.1 R/h) to 70% (at 5 R/h) for gamma elimination.

Advanced Multilayer Composite Heavy-Oxide Scintillator Detectors for High-Efficiency Fast Neutron Detection

We have developed and evaluated a new approach to fast neutron and neutron–gamma detection based on large-area multilayer composite heterogeneous detection media consisting of dispersed granules of small-crystalline scintillators contained in a transparent organic (plastic) matrix. Layers of the composite material are alternated with layers of transparent plastic scintillator material serving as light guides. The resulting detection medium—designated as ZEBRA—serves both as an active neutron converter and a detection scintillator which is designed to detect both neutrons and gamma quanta. The composite layers of the ZEBRA detector consist of small heavy-oxide scintillators in the form of granules of crystalline ZWO, BGO, GSO(Ce), and other materials. We have produced and tested the ZEBRA detector of sizes $100 \mathrm{mm} \times 100 \mathrm{mm} \times 41 \mathrm{mm}$ , and determined that they have very high efficiency of fast neutron detection (up to 49% or greater), comparable to that which can be achieved by large sized heavy-oxide single crystals of about $\varnothing 40 \times 80 \mathrm{cm}^3$ volume. We have also studied the sensitivity variation of fast neutron detection by using different types of multilayer ZEBRA detectors of 100-cm2 surface area and 41-mm thickness (with a detector weight of about 1 kg) and found it to be comparable to the sensitivity of a 3He-detector representing a total cross section of about 2000 cm2 (with a weight of detector, including its plastic moderator, of about 120 kg). The measured count rate in response to a fast neutron source of 252Cf at 2 m for the ZEBRA-GSO(Ce) detector of size $100 \mathrm{mm} \times100 \mathrm{mm} \times41 \mathrm{mm}$ was 2.84 Hz/ng of 252Cf isotope, and this count rate can be doubled by increasing the detector height (and area) up to $200 \mathrm{mm} \times100 \mathrm{mm}$ . In summary, the ZEBRA detectors represent a new type of high efficiency and low-cost large-area solid-state neutron detector that can be used for stationary neutron/gamma portals. They may represent an interesting alternative to expensive, bulky gas counters based on 3He or 10Bneutron detection technologies.

Advanced Multilayer Composite Heavy-Oxide Scintillator Detectors for High Efficiency Fast Neutron Detection

We have developed and evaluated a new approach to fast neutron and neutron-gamma detection based on large-area multilayer composite heterogeneous detection media consisting of dispersed granules of small-crystalline scintillators contained in a transparent organic (plastic) matrix. Layers of the composite material are alternated with layers of transparent plastic scintillator material serving as light guides. The resulting detection medium – designated as ZEBRA – serves as both an active neutron converter and a detection scintillator which is designed to detect both neutrons and gamma-quanta. The composite layers of the ZEBRA detector consist of small heavy-oxide scintillators in the form of granules of crystalline BGO, GSO, ZWO, PWO and other materials. We have produced and tested the ZEBRA detector of sizes 100x100x41 mm and greater, and determined that they have very high efficiency of fast neutron detection (up to 49% or greater), comparable to that which can be achieved by large sized heavy-oxide single crystals of about Ø40x80 cm3 volume. We have also studied the sensitivity variation to fast neutron detection by using different types of multilayer ZEBRA detectors of 100 cm2 surface area and 41 mm thickness (with a detector weight of about 1 kg) and found it to be comparable to the sensitivity of a 3He-detector representing a total cross-section of about 2000 cm2 (with a weight of detector, including its plastic moderator, of about 120 kg). The measured count rate in response to a fast neutron source of 252Cf at 2 m for the ZEBRA-GSO detector of size 100x100x41 mm3 was 2.84 cps/ng, and this count rate can be doubled by increasing the detector height (and area) up to 200x100 mm2. In summary, the ZEBRA detectors represent a new type of high efficiency and low cost solid-state neutron detector that can be used for stationary neutron/gamma portals. They may represent an interesting alternative to expensive, bulky gas counters based on 3He or 10B neutron detection technologies.

Expectation and Possible Issues for Development of a Compact Neutron Source

An overview of the development of the compact neutron source is briefly described. Recent development of a neutron source as well as measurement technique is opening a new era for a small neutron source as a practical probe for materials science. In order to utilize neutron beam as a research probe, there are several ingredients such as handling technique of the neutron beam, the development of time-of-flight measurement technique, and the development of high efficiency neutron detectors, and none of them can lack for a practical instrument. It is also emphasized that the protection from radiation and costs for construction as well as daily operation are two more indispensable factors to be carefully considered.

Large-Area, Low-Cost, High-Efficiency Neutron Detector for Vehicle-Mounted Operation

We have developed a large-area, low-cost, high-efficiency neutron detector for vehicle-mounted operation. The detector, which has overall dimensions 12.7 cm $\times 91.4$ cm $\times 102$ cm (5” $\times 36$ ” $\times 40$ ”), a sensitive area equal to $0.85~\text {m}^{{\mathbf {2}}}$ (1320 in2), and weight of 110 kg (242 lbs), employs an array of 90 boron-coated straw (BCS) detectors. PTI has also developed electronics to minimize cost and space while providing low-noise signal conditioning for both neutron and gamma detection channels, as well as low energy Bluetooth communication with handheld devices. Extremely low power consumption allows continuous use for 225 hours (~10 days) using three AAA lithium-ion rechargeable batteries. We present radiological, mechanical, and environmental tests, collected from four full-scale prototypes. Outdoor neutron-counting tests with a moderated 252Cf source 2 m away from the center of the detector face showed an average detection rate of 5.5 cps/ng with a standard deviation of 0.09 cps/ng over the four individual detector measurements. Measurements showed a gamma rejection ratio of $1.0\times 10^{{\mathbf {-8}}}$ , and gamma absolute rejection ratio (GARRn) of 0.93. The prototypes were also operated successfully onboard a moving vehicle for high-speed tests and a long-range 1433-mile, two-day road trip from Houston, TX, USA, to Laurel, MD, USA. Using auxiliary DARPA SIGMA equipment, the GPS, timestamp, gamma and neutron data were transmitted over the cellular network with 10 Hz resolution to a server and real-time tracking website. Mechanical impact and electrostatic discharge testing produced no spurious counts in either the neutron or gamma channels. Ambient environmental temperature testing showed less than ± 1% response variation over the range from −30°C to +55°C.