Neutron Detection Technology Research Articles

Transient Current Analysis of GaN Neutron Detector Based on the SRIM and TCAD Methods

Utilizing Technology Computer Aided Design (TCAD) software, this study determines the optimal thickness and doping concentration for the intrinsic gallium nitride (GaN) layer in a p-i-n GaN diode to improve detection efficiency and reliability. The study examines energy loss and the transient current response induced by alpha and 3H particles within the GaN p-i-n diode. Additionally, TCAD elucidates the transient current behavior arising from electron-hole pair generation, utilizing the Stopping and Range of Ions in Matter SRIM-2013 linear energy transfer distribution as a guide. The simulations disclose that the tailing effect in the transient current response results from radiation-induced hole accumulation. Elevated applied bias results in increased transient current pulse amplitude, attributed to an extended depletion region that boosts carrier collection. These insights are expected to drive advancements in GaN-based neutron detector technology, essential for advancing nuclear and space science applications in the next generation.

Robust Thermal Neutron Detection by LiInP2 Se6 Bulk Single Crystals.

Direct neutron detection based on semiconductor crystals holds promise to transform current neutron detector technologies and further boosts their widespread applications. It is, however, long impeded by the dearth of suitable materials in the form of sizeable bulk crystals. Here, we have developed high-quality centimeter-sized LiInP2 Se6 single crystals using the Bridgman method and systematically investigated their structure and property characteristics. The prototype detectors fabricated from the crystals demonstrate an energy resolution of 53.7% in response to α-particles generated from an 241 Am source and robust, well-defined response spectra to thermal neutrons that exhibit no polarization or degradation effects under prolonged neutron/γ-ray irradiation. We have also identified the primary mechanisms of Se-vacancy and InLi antisite defects in the carrier trapping process. Such insights are critical for further enhancing the energy resolution of LiInP2 Se6 bulk crystals towards the intrinsic level (∼8.6% as indicated by our chemical vapor transport-grown thin crystals). These results pave the way for practically adopting LiInP2 Se6 single crystals in new-generation solid-state neutron detectors. This article is protected by copyright. All rights reserved.

Manhattan Project 1940s research on the prompt fission neutron spectrum

We describe how the prompt fission neutron spectrum (PFNS) was determined for the Manhattan Project at Los Alamos. Early work before World War II at American and British universities is described, together with theoretical work by Feather at Cambridge and Bethe at Los Alamos. As the Manhattan Project was being planned in 1942, two experiments on natural uranium were commissioned that proved to be influential: 1) An integral experiment at Chicago by Christy and Manley that accurately determined the average PFNS spectrum energy, 2.2 ± 0.2 MeV; 2) Bloch and Staub’s Stanford cyclotron measurement of the PFNS spectrum, which obtained an average energy of 1.70 ± 0.34 MeV. These two papers, previously unavailable outside of Los Alamos, are reproduced in the Supplementary Appendix. From these data, at the beginning of the project in 1943 Serber estimated an average 235U PFNS energy of 2 MeV, and indeed this agrees with today’s best estimate. The challenges facing the scientists involved both the availability of only very small samples of enriched uranium and plutonium targets, and fast neutron detection technologies. During the project, 235U and 239Pu PFNS were measured by Nicodemus and Staub. These also proved to be quite accurate and gave an average spectrum energy of 2 MeV for 235U. [This is not reproduced in the Appendix because it was published after the war in Physical Review 89, 1288 (1953)]. New methods were developed to enable more accurate measurements, and this paper describes how the PFNS was determined surprisingly well by 1945. We end by describing the post-war measurements in the 50s, including the PFNS data used by Ford and Wheeler in their simulations in 1951, the Bonner 1952 data, the seminal 1952 Watt paper with a new empirical parametrization of the PFNS, and the accurate PFNS measurement undertaken at Los Alamos by Cranberg et al. in 1956. We compare the measurements with our best understanding today as embodied in the Evaluated Nuclear Data File ENDF/B-VIII.0. Some images from historical documents in our Los Alamos National Security Research Center (NSRC) archives are shown.

Sub-ps Pulsed Laser Deposition of Boron Films for Neutron Detector Applications.

In view of the demand for high-quality thermal neutron detectors, boron films have recently attracted widespread research interest because of their special properties. In this work, we report on the deposition of boron films on silicon substrates by sub-picosecond pulsed laser deposition (PLD) at room temperature. Particular emphasis was placed on the investigation of the effect of the laser energy density (fluence) on the ablation process of the target material, as well as on the morphological properties of the resulting films. In addition, based on the study of the ablation and deposition rates as a function of the fluence, the ablation/deposition mechanisms are discussed. We show that well-adherent and stable boron films, with good quality surfaces revealing a good surface flatness and absence of cracks, can be obtained by means of the PLD technique, which proves to be a reliable and reproducible method for the fabrication of thick boron coatings that are suitable for neutron detection technology.

Double-GEM based thermal neutron detector prototype

The Helium-3 shortage and the growing interest in neutron science constitute a driving factor in developing new neutron detection technologies. In this work, we report the development of a double-GEM detector prototype that uses a 10B4C layer as a neutron converter material. GEANT4 simulations were performed predicting an efficiency of (3.14 ± 0.10)%, agreeing within 2.7σ with the experimental and analytic detection efficiencies obtained by the detector when tested in a 41.8 meV thermal neutron beam. The detector is position sensitive, equipped with a 256+256 strip readout connected to resistive chains, and achieves a spatial resolution better than 3 mm. The gain stability over time was also measured with a fluctuation of about 0.2% h-1 of the signal amplitude. A simple data acquisition with only 5 electronic channels is sufficient to operate this detector.

Advances in acoustically-tensioned metastable detector neutron detection technology

Nuclear security, the prevention of special nuclear material (SNM) smuggling, at borders and ports has been described as one of the 21st century grand challenges. Currently, thermal neutron detectors (a majority of which are He-3 detectors), are used to monitor for neutrons emitted from special nuclear materials. He-3 neutron absorption cross-sections are ∼103 times higher for thermal vs fast neutrons; as such, moderated He-3 detectors must suffer from reduced efficiency (due to scattering and absorption in moderators) for detection of fast neutrons emitted from fission of SNMs. Development of a real-time high-efficiency gamma/beta blind, directionality-determining thermal and fast neutron monitoring system without need for bulky moderation is needed to allow for optimal SNM monitoring. The previously developed economical acoustically tensioned metastable fluid detector (E-ATMFD(Ver.0), offered all of these capabilities but exhibited low (∼0.01–0.05%) efficiencies than conventional neutron monitors. Design optimization guided via coupled multiphysics-neutron transport simulation tools, together with devising a figure of merit algorithm, experimental validation work with various reflector shapes, and a novel detection fluid “DFP”, the direct drive E-ATMFD(Ver.1) architecture was devised and demonstrated to offer ∼5 to 27x improvement in neutron detection efficiency. Using borated DFP mixture version E-ATMFD(Ver.1B), epithermal to fast neutron detection capabilities were demonstrated — effectively extending the sensitivity to all energies of neutrons and increasing the efficiency by another factor of up to ∼2.5. Further research included development of a novel frequency sweep-cum-rate drive mode to successfully operate multiple E-ATMFDs simultaneously from a single power source; resulting in a further 4x detection efficiency improvement from enhanced scattering and electromagnetic coupling — showing potential for enabling large array mode SNM interrogation.

Pulsed neutron source from interaction of relativistic laser pulse with micro-structure assisted pitcher–catcher target

Neutron detection technology is a powerful method for characterizing fundamental and industrial materials, such as magnetic materials, nanomaterials, polymers, and biological substances. A compact pulsed neutron source is desired, as the traditional way of producing high-yield neutrons depends mainly on large-scale accelerators or fission reactors. Here, we propose a scheme to generate a high-yield pulsed neutron source by using a 100 fs relativistic laser pulse interacting with a micro-structure assisted pitcher–catcher target. Three-dimensional particle-in-cell and Monte Carlo hybrid simulations demonstrate that an energetic deuterium ion beam with a cutoff energy of 75 MeV and a 7.23 laser-to-deuterium energy conversion efficiency can be obtained with a laser pulse of intensity W cm−2, duration 330 fs, power 34 TW and energy 6.7 J. When they strike the following lithium fluoride converter of thickness 2 cm, a large number of neutrons are thus produced via a 7Li(d,n) nuclear reaction. The neutron yield is up to 109 and its pulse duration is as short as 20 ps. This scheme could be realized in laboratories with current hundreds-of-terawatt or multi-petawatt laser facilities.

Boron nitride neutron detector with the ability for detecting both thermal and fast neutrons

The detection of fast neutrons is regarded technically challenging because the interaction probability of fast neutron with matter is extremely low. Based on our recent development of hexagonal boron nitride (BN) semiconductor thermal neutron detectors with a record high efficiency of 59%, we report here the feasibility studies of BN detectors for detecting fast neutrons. A BN detector with a detection area of 2.1 cm2 was fabricated from a 90 μm thick BN epilayer. In the presence of a bare Cf-252 source emitting fast neutrons ranging from 1 to 9 MeV, the detection efficiency was estimated to be about 0.1%. The measured mean free path of fast neutron in BN is about 7.6 cm. Together with the capability of BN for thermal neutron detection, the present results indicate that by incorporating BN with a large thickness, BN neutron detectors are expected to possess the unique capability of directly detecting thermal to fast neutrons as well as outstanding features resulting from the ultrawide bandgap of BN. The identification of a single material that is sensitive to both thermal and fast neutrons is valuable for the development of novel neutron detection technologies.

Research and Application of Neutron Detection Technology in Inspection of Void Defects in Turbine Runner Chamber

After a long-term operation of the turbine runner chamber, there may be voids between the steel lining and the concrete. If it is not discovered and treated in time, the safe and stable operation of the unit will be affected. In engineering practice, the hammering method is often used to detect hole defects, and the accuracy is low. The neutron detection technology is proposed to detect the void defects of the steel lining, quantitatively display the void location and size, and improve the accuracy of void defect detection.

Discrimination of neutrons and gamma-rays in plastic scintillator based on falling-edge percentage slope method

With the development of neutron detection technology, the demand for real-time and fast neutron gamma discrimination has become of increasing importance. In this study, neutron and gamma pulse signals measured by an EJ299-33A plastic scintillator detector were analyzed via Matlab off-line. This study compares the effects of seven fast neutron and gamma (n/γ) discrimination methods; (i) charge comparison method, (ii) time-domain oriented method, (iii) amplitude oriented method, (iv) pulse time–amplitude two types of width method, (v) angle difference method, (vi) falling-edge numerical integral method, and, lastly, (vii) falling-edge percentage slope method proposed in this study. We verified that filtering and amplitude normalization improve the discrimination quality but consume much time that accounts for 99.6% of the total discrimination time. The proposed method was compared with other six methods in two aspects: (i) the figure of merit (FoM), (ii) the discrimination time. The FoM value and time consumption of the falling-edge percentage slope method with amplitude normalization are 1.26 and 0.0621s, respectively, while an unnormalized FoM value is 1.02. Experimental results showed that compared with all aforementioned methods, the FOM value of our proposed method is the second high followed the charge comparison method, retaining a short discrimination time which is only half of that of the charge comparison method. This relatively short time consuming is on account of its low volume of data storage and calculation. Generally, the falling-edge percentage slope method has a good discrimination performance while consumes little time, which is capable to be implemented on real-time discrimination applications.

Boron-Loaded Polymeric Sensor for the Direct Detection of Thermal Neutrons.

We report the first demonstration of a solid-state, direct-conversion sensor for thermal neutrons based on a polymer/inorganic nanocomposite. Sensors were fabricated from ultrathick films of poly(triarylamine) (PTAA) semiconducting polymer, with thicknesses up to 100 μm. Boron nanoparticles (NPs) were dispersed throughout the PTAA film to provide the neutron stopping power arising from the high thermal neutron cross section of the isotope 10B. To maximize the quantum efficiency (QE) of the sensor to thermal neutrons, a high volume fraction of homogeneously dispersed boron nanoparticles was achieved in the thick PTAA film using an optimized processing method. Thick active layers were realized using a high molecular weight of the PTAA so that molecular entanglements provide a high cohesive strength. A nonionic surfactant was used to stabilize the boron dispersion in solvent and hence suppress the formation of agglomerates and associated electrical pathways. Boron nanoparticle loadings of up to ten volume percent were achieved, with thermal neutron quantum efficiency estimates up to 6% resulting. The sensors' neutron responses were characterized under a high flux thermal neutron exposure, showing a linear correlation between the response current and the thermal neutron flux up to ∼107 cm-2 s-1. Polymer-based boron nanocomposite sensors offer a new neutron detection technology that uses low-cost, scalable solution processing and provides an alternative to traditional neutron sensors that use rare isotopes, such as 3He.

Direct thermal neutron detection by the 2D semiconductor 6LiInP2Se6.

Highly efficient neutron detectors are critical in many sectors, including national security1,2, medicine3, crystallography4 and astronomy5. The main neutron detection technologies currently used involve 3He-gas-filled proportional counters6 and light scintillators7 for thermalized neutrons. Semiconductors could provide the next generation of neutron detectors because their advantages could make them competitive with or superior to existing detectors. In particular, solids with a high concentration of high-neutron-capture nuclides (such as 6Li, 10B) could be used to develop smaller detectors with high intrinsic efficiencies. However, no promising materials have been reported so far for the construction of direct-conversion semiconductor detectors. Here we report on the semiconductor LiInP2Se6 and demonstrate its potential as a candidate material for the direct detection of thermal neutrons at room temperature. This compound has a good thermal-neutron-capture cross-section, a suitable bandgap (2.06 electronvolts) and a favourable electronic band structure for efficient electron charge transport. We used α particles from an 241Am source as a proxy for the neutron-capture reaction and determined that the compact two-dimensional (2D) LiInP2Se6 detectors resolved the full-energy peak with an energy resolution of 13.9 per cent. Direct neutron detection from a moderated Pu-Be source was achieved using 6Li-enriched (95 per cent) LiInP2Se6 detectors with full-peak resolution. We anticipate that these results will spark interest in this field and enable the replacement of 3He counters by semiconductor-based neutron detectors.

High-rate measurements of the novel BAND-GEM technology for thermal neutron detection at spallation sources

Thermal neutron detection technologies alternative to 3He, featuring a rate capability matching the high flux expected at the European Spallation Source (ESS), are one of the main present challenges of neutron science. A new thermal neutron detection technology was recently developed named the BAND-GEM, a Gas Electron Multiplier (GEM)-based detector provided with a borated 3D converter to reach high efficiency. In this paper the results of a count rate test performed on the BAND-GEM at the ORPHEE reactor are presented. The results show that the detector can easily reach a neutron count rate of 2 MHz/cm2 while maintaining a good linearity and it is able to reach 8 MHz/cm2 with a measurable loss of linearity η and with no sign of instability.

Proton Light Yield of Fast Plastic Scintillators for Neutron Imaging

Plastic organic scintillators have been tailored in composition to achieve ultra-fast temporal response, thereby enabling the design and development of fast neutron detection systems with high timing resolution. Eljen Technology's plastic organic scintillators -- EJ-230, EJ-232, and EJ-232Q -- are prospective candidates for use in emerging neutron imaging systems, where fast timing is paramount. To support the neutron response characterization of these materials, the relative proton light yields of EJ-230, EJ-232, and EJ-232Q were measured at the 88-Inch Cyclotron at Lawrence Berkeley National Laboratory. Using a broad-spectrum neutron source and a double time-of-flight technique, the proton light yield relations were obtained over a proton recoil energy range of approximately 300 keV to 4 MeV. The EJ-230, EJ-232, and EJ-232Q scintillators exhibited similar proton light yield relations to each other as well as to other plastic scintillators with the same polymer base material. A comparison of the relative proton light yield of different sized cylindrical EJ-232 and EJ-232Q scintillators also revealed consistent results. This work provides key input data for the realistic computational modeling of neutron detection technologies employing these materials, thereby supporting new capabilities in near-field radionuclide detection for national security applications.

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.

Design and performance considerations for dual-sided microstructured semiconductor neutron detectors

Thin-film-coated solid-state thermal neutron detectors were replaced in recent decades with the Microstructured Semiconductor Neutron Detector (MSND) technology. The basic device structure of the MSND involves micro-sized trenches that are etched into a vertically-oriented pvn-junction diode that are backfilled with a neutron converting material. Neutrons absorbed within the converting material induce fission of the parent nucleus, producing a pair of energetic charged-particle reaction products that can be counted by the diode. The deep-etched microstructures of the MSND yield good neutron-absorption efficiency and reaction-product counting efficiency, resulting in a 6-10x improvement in intrinsic thermal-neutron detection efficiency over thin-film-coated devices. Performance of present-day MSNDs are reaching an efficiency plateau; streaming paths between the conversion-material backfilled trenches, allow a considerable fraction of neutrons to pass through the device undetected. Dual-Sided Microstructured Semiconductor Neutron Detectors (DS-MSNDs) have been developed that utilize a complementary second set of trenches on the back-side of the device to capture streaming neutrons. This work investigates several of the fundamental design structures that can be etched into the semiconductor material, including repeated front-side and back-side patterns and inverse microfeature patterns. Results from MCNP6 simulations of DS-MSNDs show that intrinsic thermal-neutron detection efficiencies are often double that of their MSND counterparts and greater than 80% intrinsic thermal-neutron detection efficiency is theoretically possible with a 1.5-mm thick device.

Spatially resolved time-of-flight neutron imaging using a scintillator CMOS-camera detector with kHz time resolution.

We herein report on using a compact and low cost scintillator-camera based neutron detection system for quantitative time-of-flight imaging applications. While powerful pulsed neutron sources emerge and enable unprecedented scientific achievements, one bottleneck is the availability of suitable detectors that provide high count- and high frame- rate capabilities. For imaging applications the achievable spatial resolution/pixel size is obviously another key characteristic. While major effort was so far directed towards the development of neutron counting type imaging detectors, this work demonstrates that a camera based detector system as commonly employed at steady state sources can also be used if a suitable camera is utilized. This is demonstrated at the ESS test beamline (V20) at Helmholtz-Zentrum Berlin by recording the time-of-flight transmission spectrum of steel samples using a CMOS camera at 1 kHz frame rate, revealing the characteristic Bragg edge pattern. This 'simple' setup in the current state presents a useful option of neutron detection and has the potential to overcome many of the existing limitations and could provide a reliable alternative for neutron detector technology in general, given that the camera and scintillator technology keep up the current development speed.

Performance evaluation of the Boron Coated Straws detector with Geant4

The last decade has witnessed the development of several alternative neutron detector technologies, as a consequence of upcoming neutron sources and upgrades, as well the world-wide shortage of $^3$He. One branch of development is the family of $^{10}$B-based gaseous detectors. This work focuses on the boron coated straws (BCS) by Proportional Technologies Inc., a commercial solution designed for use in homeland security and neutron science. A detailed Geant4 simulation study of the BCS is presented, which investigates various aspects of the detector performance, e.g. efficiency, activation, absorption and the impact of scattering on the measured signal. The suitability of the BCS detector for Small Angle Neutron Scattering (SANS), direct chopper spectrometry and imaging is discussed.

Passive Gamma-Ray and Neutron Imaging Systems for National Security and Nuclear Non-Proliferation in Controlled and Uncontrolled Detection Areas: Review of Past and Current Status.

Global concern for the illicit transportation and trafficking of nuclear materials and other radioactive sources is on the rise, with efficient and rapid security and non-proliferation technologies in more demand than ever. Many factors contribute to this issue, including the increasing number of terrorist cells, gaps in security networks, politically unstable states across the globe and the black-market trading of radioactive sources to unknown parties. The use of passive gamma-ray and neutron detection and imaging technologies in security-sensitive areas and ports has had more impact than most other techniques in detecting and deterring illicit transportation and trafficking of illegal radioactive materials. This work reviews and critically evaluates these techniques as currently utilised within national security and non-proliferation applications and proposes likely avenues of development.

Recent progress in the commercialization of the Li Foil multi-wire proportional counter neutron detectors

The scarcity and rising cost of 3He gas has introduced a push in alternative neutron detector technologies. The Li foil multi-wire proportional counter (Li Foil MWPC) neutron detectors have shown promise as a 3He replacement technology. Large, gas-filled proportional counters with five layers of 75 µm thick 6Li foils have been built and characterized, yielding over 55% thermal neutron detection efficiency, with the possibility of increasing the efficiency above 70% with ten 96% enriched 6Li foil layers. Most recently, a backpack radiation detector (BRD) was fabricated, equipped with four Li Foil MWPC devices. The neutron sensitivity-to-weight ratio of the Li Foil MWPC devices was first optimized using MCNP6 by simulating the angular response to an ANSI-moderated-252Cf source positioned 1.5 m away from the devices. The simulated neutron sensitivity results were compared and benchmarked to that of the commercially-available Thermo-Fisher PackEye v. 1.0 that contains two 14 in. long, 2 in. diameter, 2.5 atm 3He tubes. The experimental efforts studied the performance of the Li Foil MWPCs in the backpack instrument configuration. Fabrication advancements were implemented to the Li Foil MWPC devices to increase the device manufacturability and improve the commercialization capabilities. These advancements included weight reduction, new hermetic sealing techniques, optimizing active area, and anode wire cost reduction. The Li Foil MWPC BRD was evaluated as a part of a PNNL test campaign for neutron sensitivity where 0.36 cps/ng of 252Cf at 1.5 m was measured. The gamma-ray rejection ratio (GRR) of the BRD was also evaluated, yielding a measured value of 3.1 × 10−8 for a 137Cs exposure rate of 50 mR/Hr. Further evaluations were performed under the PNNL test campaign including detector response to neutron sources of 252Cf, AmBe, AmLi and WGPu, detector angular response, and the gamma absolute rejection ratio in the presence of neutrons (GARRn).