Neutron Converter Research Articles

Solid-State Neutron Detection Based on Methylammonium Lead Bromide Perovskite Single Crystals.

Perovskite-based semiconductors, such as methylammonium and cesium lead halides (MPbX3: M = CH3NH3+ or Cs+; X = I-, Br-, or Cl-), have attracted immense attention for several applications, including radiation detection, due to their excellent electronic and optical properties.1,2,3,4,5,6 In addition, the combination of perovskites with other materials enables unique device structures. For example, robust and reliable diodes result when combined with metal oxide semiconductors. This device can be used for detection of nonionizing and ionizing radiation. In this paper, we report a unique perovskite single-crystal-based neutron detector using a heterojunction diode based on single-crystal MAPbBr3 and gallium oxide (Ga2O3) thin film. The MAPbBr3/Ga2O3 diodes demonstrate a leakage current of ∼7 × 10-10 A/mm2, an on/off ratio of ∼102, an ideality factor of 1.41, and minimal hysteresis that enables alpha particle, gamma-ray, and neutron detection at a bias as low as (-5 V). Gamma discrimination is further improved by 85% by optimizing the thickness of the perovskite single crystal. The MAPbBr3/Ga2O3 diodes also demonstrate a neutron detection efficiency of ∼3.92% when combined with a 10B neutron conversion layer.

Performance Testing of Dysprosium-Based Scintillation Screens and Demonstration of Digital Transfer Method Neutron Radiography of Highly Radioactive Samples

Scintillator screens consisting of a dysprosium neutron converter and various scintillator materials were tested in the Heinz Maier-Leibnitz Zentrum Forschungsreaktor München II (FRM II) ANTARES cold neutron beam with the goal of finding a suitable screen for digital transfer method neutron radiography. This work explores the cold neutron response of 16 scintillator screens, 7 of which were previously tested with thermal neutrons. Light yield, signal-to-noise ratio (SNR), and spatial resolution were measured to compare the scintillator screens and determine which were best suited for digital transfer method neutron radiography. Screens with a zinc sulfide (ZnS:Cu) scintillator were most suitable for digital transfer method radiography based on light output, spatial resolution, SNR, and gamma-ray insensitivity. Spatial resolutions between 65 and 220 μm were measured. The top-performing screens were then used to demonstrate the feasibility of a new digital transfer method neutron radiography to image highly radioactive (8.84 Sv/h at ≈1 cm) nuclear fuel at Idaho National Laboratory’s Neutron Radiography reactor (NRAD). These results suggest that digital transfer method neutron radiography can be used to indirectly image highly radioactive objects and/or use neutron beams with a large gamma-ray content on a timescale of ~10 min/image (~144 images/day), much faster than the >10 h required using the current transfer method with film (limited to ~14 radiographs/day at NRAD).

Efficiency limitation of thin film coated planar semiconductor thermal neutron detector

Semiconductor thermal neutron detectors are increasingly been used in in-core thermal neutron flux measurements in nuclear reactors. One limitation of these detectors is that they suffer from low detection efficiency. In this work, the maximum efficiency of a planar structure thermal neutron detector was determined using two widely used computer codes: Geant4 and MCNP6. Diamond and SiC are used as based materials in this work because of their large electron-hole pair production efficiency which generally translates to high detection efficiency. The electron-hole pair production efficiency is the fraction of energy that goes into electron-hole pair creation and depends on the band-gap energy and the W-values. These two materials are also not susceptible to radiation damage which makes them suitable for high radiation environments such as nuclear reactors. Thermal neutron detection is achieved using 10B and 6LiF conversion layers coated on the surface of the detector. The maximum efficiency for 10B conversion layer was achieved at a thickness of 2 μm. The efficiency at this thickness is 5.57 ± 0.09% and 5.49±0.09% for diamond and silicon carbide, respectively. When 6LiF was used as a thermal neutron conversion layer, the maximum thickness of the conversion layer was determined to occur at 17 μm. The efficiency at this thickness is 5.47 ±0.06% and 5.38±0.06% for diamond and SiC, respectively.

Neutron conversion–diffusion: a new model for structured short gamma-ray burst jets compatible with GRB 170817

ABSTRACT We present a generic theoretical model for the structuring of a relativistic jet propagating through the ejecta of a binary neutron star merger event, introducing the effects of the neutron conversion–diffusion, which provides a baryon flux propagating transversely from the ejecta towards the jet axis. This results naturally in an increased baryon load structure of the outer jet with the approximate isotropic energy distribution Eiso(θ) ∝ θ−4, which is compatible with the first gravitational wave and short gamma-ray burst event GW170817/GRB 170817A observed at an off-axis angle of the jet.

Emerging Trends in Nano Structured Silicon Detectors for Neutron Spectroscopy

Neutron detectors are extensively used in numerous applications such as, in nuclear fuels plants, high energy accelerators, space explorations, imaging etc. Among the commercially available various detectors, 3D semiconductor detectors filled with an appropriate neutron converter layer were been studied over several years as they are highly sensitive small sensors and could provide high spectroscopic resolution and energy information with respect to the neutron spectrum of our interest. This paper reviews the current status of the nano structured silicon (Si) neutron detectors in consideration with their potential application in neutron spectroscopy. It includes a thorough review on simulation and experimental studies that were already reported in several literatures to analyse the primary radiation induced imperfections which can modify the response of a Si based detector.

Principal Component Analysis applied to neutron dosimetry based on PADC detectors and FNTDs

Solid State Nuclear Track Detectors (SSNTD) have been used as passive dosimeters for many decades. Fast neutron detection is performed by detecting recoil protons generated in a hydrogenous material (neutron converter). The dose is estimated by multiplying the recoil protons track-spots density present on the detector surface by a calibration coefficient obtained from reference irradiations. Therefore, one needs to automatically and reliably discriminate between the track-spots induced by recoil-protons and the spurious signal engendered either by material imperfections or by other ionising particles interactions. The objective of this work is to demonstrate and apply a method, based on the multivariate statistical tool named Principal Component Analysis (PCA), aiming at identifying and filtering out the spurious signal in track detectors. The advantage of this approach is that it can be applied to any type of SSNTD, provided apt definition of initial physical variables describing each track-spot. To show that, we applied the method to poly-allyl diglycol carbonate (PADC) detectors, to filter the signal generated by material imperfections, and to fluorescence nuclear track detectors (FNTDs), to remove the signal induced by other radiation field components. After filtering, dose assessments were compared with reference values of exposures, showing satisfactory agreement. In case of the FNTDs, the procedure proved to be effective regardless of the crystal colouration, which is known to affect signal-rejection techniques based on track-spots fluorescence intensity. The technique also offers the advantage of self-adjusting the filtering parameters based on the currently analysed detector set, as long as calibration and unirradiated detectors are included in the dataset.

Timepix3 detector network for nuclear waste monitoring

In the framework of the MICADO project we proposed an active long-term nuclear waste monitoring system based on Timepix3 technology. Particle detectors based on Timepix3 are capable of particle type discrimination and provide spectrometric information in combination with precise timing information. To maximize the versatility of the setup, the Timepix3 detectors employed are equipped with a range of different sensors. To enable measurement of neutrons, two quadrants of the detectors are covered by neutron converters, allowing detection of thermal neutron by capture in 6Li, as well as detection of fast neutrons through recoil protons generated in a polyethylene converter. Within this project a new housing for the detector unit and the readout was developed, with the network currently comprising of 9 such detectors. A specifically developed in-house software handles simultaneous operation of all devices, cluster analysis and data visualization. Energy calibration was performed using an X-ray tube with several fluorescence foils as well as photons from an 241Am source. The neutron and gamma/X-ray detection efficiency calibration was carried out at the Czech Metrology Institute and the results are presented here. Tests on simultaneous operation of all 9 devices were performed using uraninite and 241Am sources.

Design and first tests of the S3 detector of reactor antineutrinos

The new experiment S3 devoted to the study of reactor antineutrinos was designed and constructed as a common activity of IEAP CTU in Prague and JINR (Dubna). The S3 detector is a compact, highly segmented polystyrene-based scintillating detector composed of 80 detector elements with a gadolinium neutron converter between elements layers. A positron and a neutron are produced in an inverse beta decay initiated with an electron antineutrino in the detector. A modular multi-channel fast ADC was developed for the data acquisition for the whole 80-channel S3 detector and the 4-channel cosmic veto system. The detector meets very strict safety rules of nuclear power plants and can be installed in a chamber located immediately under the reactor. The close vicinity from the reactor enables to study neutrino properties with a higher efficiency, to investigate neutrino oscillations at short baselines and try to verify the hypothesis of a sterile neutrino. The details of the design and construction of the S3 detector, as well as properties of the modular multi-channel fast ADC system, and first tests of the device are presented.

SILICON CARBIDE NEUTRON DETECTOR PROTOTYPE TESTING AT THE JSI TRIGA REACTOR FOR ENHANCED BORDER AND PORTS SECURITY

In 2016, the “E-SiCure” project (standing for “Engineering Silicon Carbide for Border and Port Security”), funded by the NATO Science for Peace and Security Programme was launched. The main objective is to combine theoretical, experimental and applied research towards the development of radiation-hard SiC-based detectors of special nuclear materials (SNM), with the end goal to enhance border and port security barriers. Prototype neutron detectors, configured as 4H-SiC-based Schottky barrier diodes, were developed for the detection of secondary charged particles (tritons, alphas and lithium atoms) which are the result of thermal neutron reactions on 10B and 6LiF layers above the surface of the 4H-SiC diodes. We designed a stand-alone prototype detection system, consisting of a preamplifier, shaping amplifier and a multichannel analyser operated by a laptop computer, for testing of neutron detector prototypes at the Jožef Stefan Institute (JSI) TRIGA reactor using a broad beam of reactor neutrons. The reverse bias for the detector diode and the power to electronic system were provided by a standalone battery-powered voltage source. The detector functionality was established through measurements using an 241Am alpha particle source. Two dedicated experimental campaigns were performed at the JSI TRIGA reactor. The registered pulse height spectra from the detectors, using both 10B and 6LiF neutron converting layers, clearly demonstrated the neutron detection abilities of the SiC detector prototypes. The computed neutron detection sensitivity of the single prototype detectors demonstrates that scaling SiC detectors into larger arrays, of dimensions relevant for border and port radiation detectors, could enable neutron sensitivity levels matching gas-based detector technology.

Boron-Based Neutron Scintillator Screens for Neutron Imaging.

In digital neutron imaging, the neutron scintillator screen is a limiting factor of spatial resolution and neutron capture efficiency and must be improved to enhance the capabilities of digital neutron imaging systems. Commonly used neutron scintillators are based on 6LiF and gadolinium oxysulfide neutron converters. This work explores boron-based neutron scintillators because 10B has a neutron absorption cross-section four times greater than 6Li, less energetic daughter products than Gd and 6Li, and lower γ-ray sensitivity than Gd. These factors all suggest that, although borated neutron scintillators may not produce as much light as 6Li-based screens, they may offer improved neutron statistics and spatial resolution. This work conducts a parametric study to determine the effects of various boron neutron converters, scintillator and converter particle sizes, converter-to-scintillator mix ratio, substrate materials, and sensor construction on image quality. The best performing boron-based scintillator screens demonstrated an improvement in neutron detection efficiency when compared with a common 6LiF/ZnS scintillator, with a 125% increase in thermal neutron detection efficiency and 67% increase in epithermal neutron detection efficiency. The spatial resolution of high-resolution borated scintillators was measured, and the neutron tomography of a test object was successfully performed using some of the boron-based screens that exhibited the highest spatial resolution. For some applications, boron-based scintillators can be utilized to increase the performance of a digital neutron imaging system by reducing acquisition times and improving neutron statistics.

Thermal neutron measurement by single crystal CVD diamond detector applied with the pulse shape discrimination during deuterium plasma experiment in LHD

Abstract The Pulse shape discrimination (PSD) technique for single crystal CVD diamond detector (SDD) was applied to the real-time thermal neutron measurement during the 3rd campaign of Deuterium-Deuterium (D-D) plasma experiment in the Large Helical Device (LHD). The PSD method is based upon the different shape of electrical pulses produced in diamond by gamma-ray (triangular-shaped pulse) and energetic ions (rectangular-shaped pulse), respectively. An improved PSD was developed which makes use of the full width at half maximum (FWHM) and the full width at 2/3 of the peak height (FW2/3 PH). These two parameters reflect the difference in the pulse shape produced by gamma-rays and energetic ions. The performance of this improved PSD technique was first tested irradiating the SDD by gamma-rays from 60Co and alphas from 241Am radiation sources, respectively. Then, using a 6LiF thermal neutron converter, a successful discrimination between gamma-rays and alpha particles and tritons generated by the 6Li(n,α)3H reaction induced by neutrons from 252Cf spontaneous fission neutron source was achieved. Thanks to this PSD processing technique, the thermal neutron detection efficiency increased about 1.7 times compared to previous measurements performed without the PSD technique. The real-time thermal neutron measurement by SDD with this enhanced PSD processing was also used during D-D plasma discharges in the Large Helical Device (LHD). It was found that both the time integrated counts and the time evolution count rate measured by the SDD reproduced well that of the fission chamber used as official LHD neutron monitor. The capability of the SDD detector using the PSD technique of precise real-time thermal neutron measurement in LHD was demonstrated.

Development of a Two-Dimensional Thermal-Neutron Detector with an Entrance Window of 600 × 600 mm

A two-dimensional thermal-neutron detector developed for a small-angle diffractometer by the Petersburg Nuclear Physics Institute is described. The detector, with a sensitive area of 600 × 600 mm2, is based on a multiwire proportional chamber. A gas mixture containing 3He is the neutron converter. A new technology for manufacturing electrodes has been developed and used to increase both the gas purity and the lifetime of the detector without refilling its working volume under the experimental conditions. Data acquisition is carried out by the readout system based on the method of cathode-strip data readout to an LC delay line, which is located inside the detector. The detector is operable in a vacuum owing to its design.

Measurements of D–D fusion neutrons generated in nanowire array laser plasma using Timepix3 detector

We present the results of neutron detection in a laser plasma experiment with a CD2 nanowire target. A hybrid semiconductor pixel detector Timepix3 covered with neutron converters was used for the detection of neutrons. D–D fusion neutrons were detected in a polyethylene converter through recoiled protons. Both the energy of recoiled protons and the time-of-flight of neutrons (and thus their energy) were determined. We report (2.4±1.8)×107 neutrons generated for 1 J of incoming laser energy. Furthermore, we proved that Timepix3 is suitable for difficult operational conditions in laser experiments.

Initial development and testing of dysprosium-based scintillators for digital transfer method neutron imaging

A new type of scintillator screen consisting of a ZnS scintillator with a dysprosium neutron converter is explored in a joint effort between Idaho National Laboratory (INL) and Paul Scherrer Institute (PSI). In contrast with a traditional prompt 6Li or Gd converters, a dysprosium converter generates a latent image as neutron activated dysprosium produces an isotope which decays with half-lives of 1.26 min and 2.3 h and the decay radiation excites the ZnS scintillator. The activated scintillator screen is physically transported out of the neutron beam and away from radioactive samples into the imaging apparatus and emits photons as the screen decays, which are read by a digital camera. This technology bridges the gap between traditional indirect transfer radiography and modern digital camera-based systems. This paper describes initial development of dysprosium-based scintillator screens and the results of initial tests performed at PSI. Some screen variants exhibit sufficient light output to produce good quality radiographs in a matter of minutes. The basic spatial resolution measured using a Siemens star is approximately 300μm. This work demonstrates for the first time that indirect digital transfer method neutron imaging is a plausible method of imaging highly radioactive sources such as irradiated nuclear fuel.

Large-Scale Boron-Lined Neutron Detection Systems as a 3He Alternative for Cosmic Ray Neutron Sensing

Cosmic-Ray neutron sensors are widely used to determine soil moisture on the hectare scale. Precise measurements, especially in the case of mobile application, demand for neutron detectors with high counting rates and high signal-to-noise ratios. For a long time Cosmic Ray Neutron Sensing (CRNS) instruments have relied on $^3$He as an efficient neutron converter. Its ongoing scarcity demands for technological solutions using alternative converters, which are $^6$Li and $^{10}$B. Recent developments lead to a modular neutron detector consisting of several $^{10}$B-lined proportional counter tubes, which feature high counting rates via its large surface area. The modularity allows for individual shieldings of different segments within the detector featuring the capability of gaining spectral information about the detected neutrons. This opens the possibility for active signal correction, especially useful when applied to mobile measurements, where the influence of constantly changing near-field to the overall signal should be corrected. Furthermore, the signal-to-noise ratio could be increased by combining pulse height and pulse length spectra to discriminate between neutrons and other environmental radiation. This novel detector therefore combines high-selective counting electronics with large-scale instrumentation technology.

Characterization of a real-time neutron detector for boron neutron capture therapy using a thin silicon diode

A real-time neutron detector was developed to measure an intense neutron beam, based on both a thin silicon sensor and an extremely thin neutron converter for boron neutron capture therapy (BNCT). Neutron response function and detection efficiency were evaluated at the BNCT facility. The response function consists of neutron events, detecting both triton particles produced from the 6Li (n,t)4He reaction and alpha particles from the 10B (n,α)7Li reaction. The detector is able to clearly separate the BNCT neutron beam from coexisted gamma rays. A depth distribution of slow neutron flux in an acrylic block was experimentally obtained. While the relative depth distribution of over 20 mm in depth is in line with the results of the neutron activation measurements of gold, the absolute values are around 17% smaller than the corresponding neutron activation results, which was due to the incomplete evaluation of the neutron detection efficiency and angular-dependent response of the neutron detector.

Neutron Detection Using a Gadolinium-Cathode Gas Electron Multiplier Detector

A gas electron multiplier (GEM) detector with a gadolinium cathode has been developed to explore its potential application as a neutron detector. It consists of three standard-sized ($10\times 10$ cm${}^{2}$) GEM foils and a thin gadolinium plate as the cathode, which is used as a neutron converter. The neutron detection efficiencies were measured for two different cathode setups and for two different drift gaps. The thermal neutron source at the Korea Research Institute of Standards and Science (KRISS) was used to measure the neutron detection efficiency. Based on the neutron flux measured by KRISS, the neutron detection efficiency of our gadolinium GEM detector was $4.630 \pm 0.034(stat.) \pm 0.279(syst.) \%$.

Multilayer 10B-RPC neutron imaging detector

Resistive plate chambers (RPC) lined with 10B4C neutron converters is a promising cost-effective technology for position-sensitive thermal neutron detection capable to outperform 3He-based detectors in terms of spatial resolution and timing. However, as for the other types of gaseous detectors with a single layer of 10B4C at normal beam incidence, the detection efficiency to thermal neutrons of a single-gap 10B-RPC is only about 6%. Aiming to overcome this limitation, we introduce a multi-layer 10B-RPCs detector with a stack of ten double-gap hybrid RPCs. A description of the detector design and the results of its characterization performed at the TREFF neutron beamline at the FRM II neutron facility are presented. The results demonstrate that the detection efficiency exceeds 60% for neutrons with a wavelength of 4.7 Å and the spatial resolution (FWHM) is about 0.25 mm and 0.35 mm in the X and Y direction, respectively.

Silicon carbide neutron detector testing at the JSI TRIGA reactor for enhanced border and port security

In 2016, the NATO Science for Peace and Security Programme funded research project ”Engineering Silicon Carbide for Border and Port Security” — E-SiCure was launched, its objective being the development of radiation-hard silicon carbide (SiC) based detectors of special nuclear materials (SNM), with the aim to enhance border and port security barriers. Detector prototypes based on SiC Schottky Barrier Diodes (SBDs) and neutron converter films were developed. This paper presents the results of a dedicated experimental testing campaign performed at the Jožef Stefan Institute (JSI) TRIGA reactor in which several SiC detector prototypes equipped with 10B and 6LiF converter films were irradiated in the Dry Chamber of the reactor. The obtained results demonstrate a clearly measurable neutron response, which varies linearly with the neutron flux. The measured particle spectra from the SiC detectors exhibit a clear structure, attributable to the nature and energy of secondary particles originating as reaction products from nuclear reactions involving 10B and 6Li isotopes. The determined sensitivity of the detectors, their active volume being 1 mm × 1 mm × 25 μm, 1 mm × 1 mm × 69 μm and 1 mm × 1 mm × 170 μm, was of the order of 2 × 10−5 counts per second, per unit of neutron flux [counts s−1 per n cm−2s−1] (for neutron energies between 0 and 5 eV). Scaling the detection sensitivity by a factor of 105, i.e. to an array with a surface of around 20 cm × 2 m, comparable to large BF3 or 3He detectors, would theoretically enable an overall sensitivity of around 2 counts s−1 per n cm−2s−1, which is already comparable to typical neutron sensitivity values of gas detectors, in the range from several to over 100 counts s−1 per n cm−2s−1. Due to its outstanding tolerance to harsh environments (including high temperatures and radiation fields) and superior electronic properties when compared to other semiconductors, SiC is a promising base material for the fabrication of solid-state detectors with stable and long life-time. Improvements in sensitivity combined with the capability of fabricating large modules (SiC arrays), could make SiC an important detection technology, applicable also in the context of border and port security barrier monitoring.

10B-based films grown by pulsed laser deposition for neutron conversion applications

Solid-state neutron detectors exploit nuclear interactions producing energetic charged particles within a converter layer embedding nuclei with high neutron capture cross section and with thickness compatible with the charged particle range. Recently, boron-10 (10B) is being considered as a valid alternative to the expensive and decreasingly available 3He gas thanks to its large neutron absorption cross section and high-energy reaction products. Minimized amounts of impurities, films with optimal and well-controlled thickness, good uniformity over large areas and good adhesion to the substrates are essential to achieve efficient neutron detection performance. In this study, we present well-adherent 1-µm-thick 10B-enriched boron coatings, deposited over a large area by off-axis pulsed laser deposition (PLD) using a nanosecond Nd-YAG laser beam operating at 1064 nm and high fluence (~ 10 J/cm2), onto 1-mm-thick Al substrate as well as smooth and rough C substrates. By combining plasma plume divergence and peaked profile under off-axis deposition geometry, uniform10B films were obtained over an area of a 3.4 × 3.4 cm2. We discuss the morphological characteristics of our deposits as related to the mechanisms of nanosecond laser ablation and present energy dispersive spectroscopy (EDS) elemental analysis of the film, paying attention to the different surface features. Negligible presence of O, N and C contaminants was achieved by controlled vacuum conditions. Moreover, we present encouraging neutron detection performances of our film deposited onto Al.