Neutron Detector Research Articles

Design and performance of an epithermal neutron detector based on PFN

In this paper, an epithermal neutron detector suitable for the Prompt Fission Neutron (PFN) uranium logging method is designed by Monte Carlo simulation. According to the simulation results, the epithermal neutron detector composed of a 1 mm cadmium (Cd) layer, a 5 mm high-density polyethylene (HDPE) layer, and a 3He tube is sensitive to epithermal neutrons. Through the simulation test of Monte Carlo in formations with different uranium content, the results show that the uranium content in the formation has an obvious linear relationship with E/T, and the detection limit can meet the minimum standard for uranium ore detection. It meets the design expectation and provides a basis for the optimal design of an epithermal neutron detector.

Exploring crucial technological advancements in Anger-Camera neutron detectors for single crystal neutron diffraction

In accordance with the second phase construction blueprint for the China Spallation Neutron Source (CSNS-II), the proposal includes the establishment of a single crystal neutron diffractometer. This apparatus necessitates a neutron detector array spanning over 1 m2 and capable of covering neutron diffraction angles from 20° to 160°. Additionally, the detector's position resolution must better than 1 mm × 1 mm. To meet such requirements, a scintillator neutron detector based on the Anger-Camera principle was designed. The detector is composed of a 6LiF/ZnS (Ag) scintillation screen, optical guide, silicon photomultipliers (SiPMs) array and self-design composite compression readout electronic systems. A detector prototype, featuring a detection area of 50 mm × 50 mm, was fabricated and subjected to testing at the BL20 neutron test line in the China Spallation Neutron Source (CSNS). The detector system achieved an optimal position resolution of 0.6 mm, while the maximum count rate was approximately 20 kHz. Moreover, the detector's Bragg edge imaging capability was preliminarily investigated using stainless steel samples, demonstrating its future potential for Bragg edge transmission imaging. The proposed detector demonstrates promising potential as a candidate for the single crystal diffractometer in CSNS-II.

The Charged Particle Detection System of the SRD Module onboard the China Space Station

The radiation field environment outside the Earth varies greatly with space location and the cycle of solar activity, and the radiation environment near the space station’s orbit is much more complex than that on the Earth’s surface. Various high-energy cosmic ray particles and secondary particles produced by them and the bulkhead of the space station greatly impact the health of astronauts and the working conditions of instruments. Each aircraft is always equipped with some dedicated radiation monitoring instruments to assess the exposure risk for astronauts, and to analyze the causes of instrument failures. The Space Radiation Detector Module (SRDM) is working in the China Space Station (CSS) to measure the radiation environment inside, including two parts: the Charged Particle Detection System (CPDS) and the Neutron Detection System (NDS). The CPDS, which is the main content of this paper, contains a detector unit, that consists of three silicon detectors a BGO calorimeter, and the corresponding readout electronics unit of the detector unit. Ground test results show that the detection system can detect various charged particles from hydrogen to nitrogen ions with an energy resolution of less than 15%. The actual measurement results for a period in orbit show that the main types of charged particles in the cabin are protons and α particles, with measured energies ranging from 0.8 to 265.2 MeV for protons and from 1.0 to 61.6 MeV/A for α particles(where A is the mass number), and linear energy density (LET) range mainly from 1.0 to 612.4 keV/μm. The radiation environment data measured in CSS can provide an important reference value for the exposure risk, life science experiments, and the status of instruments on board.

Research on a Neutron Detector with a Boron-Lined Multilayer Converter

3He is a splendid neutron detection material due to its high neutron reaction cross section, gaseous state, and nonelectronegative and nonpoisonous nature. With the worldwide problem of the “3He supply crisis” arising, boron-lined gaseous neutron detectors are being widely used in neutron detection to replace 3He neutron detectors. In this work, to reduce the scattering neutron background coming from the substrate of a boron-lined neutron detector in the application of neutron scattering, a new design of the boron-lined gaseous neutron detector composed of a boron-lined multichip converter and a multiwire proportional chamber was proposed. The electron drift efficiency matrix simulated by Garfield++ (Version 2023.4) and the values and positions of electron energy deposition simulated by Geant4 were obtained. The α, 7Li, and total charged particle energy deposition spectra were acquired via coupling calculations of the electron drift efficiency matrix and the values and positions of electron energy deposition, and the width of the slit was selected as 3 mm. The boron-lined multilayer converter neutron detector (BMCND) was tested using a 241Am–239Pu mixture α source, and the total count rate of α charged particles was measured as 599.5 s−1, which is 89% of the theoretical α particle emission rate of 672.9 s−1. The drift voltage experiments showed that 1200 V is enough to acquire a relatively ideal count, and a 2500 V drift voltage was confirmed, considering the higher count and instrument safety. We also performed the neutron detection experiments using a photo-neutron source, and a characteristic spectrum shape of “two stairs” was measured. When borated polyethylene was used to shield the BMCND, the detected total count decreased while keeping the characteristic spectrum shape, demonstrating that the BMCND was equipped with the ability to detect neurons, indicating that BMCNDs have the potential to be an outstanding 3He alternative neutron detector.

Early-phase core degradation interpretation by interaction between fuel cladding and fuel components in Fukushima Daiichi nuclear power plant Unit 2

ABSTRACT The early phase of the core degradation at the Fukushima Daiichi Nuclear Power Station Unit 2 was investigated in terms of a fuel-component degradation by materials interaction by carrying out the accident analysis, evaluation of chemical conditions and experimental works. First, the accident scenario was evaluated to specify a target period (from 18:40 to 22:40 on NaN Invalid Date NaN), and then the temperature and H2/H2O pressure ratio in the core region during this period were calculated based on plant parameters. Subsequently, semi-integral experiments were performed using the mocked-up fuel components of a boiling water reactor (BWR). Furthermore, separate-effects tests using Ni-alloy/Zircaloy4 were also performed to understand the phenomenon observed in the semi-integral experiments, where the Ni-Zr reaction occurred even with the oxide layer on the Zr-based alloy. Consequently, it was estimated that the Zr-Ni eutectic melting reaction above 1100°C under steam-starved conditions resulted in a fuel failure at 19:08, melting of spacer locations at 19:37, and upper-tie-plate at 21:26. The first and second degradations could have caused the release of radioactive elements or particles leading to the neutron detection at 21:00 in front of the main gate, and the third degradation could have resulted in the separation of the upper-tie-plate.

Matrix effect correction in active neutron interrogation for residual fissile mass assessment in radioactive waste drums

Metallic waste in the form of shells and nozzles remains following the reprocessing of spent fuel at La Hague plant (France). Before the final disposal, drums containing the waste are transported to the compaction facility where its volume is reduced by a factor of 5. With the objective of controlling the criticality/safety levels, an active neutron interrogation system at the entrance of the facility is used to assess the residual fissile mass remaining in the waste, which relies on prompt fission neutron detection (known as the differential die-away technique, DDA). The measured signal is proportionally linked to the fissile mass by a calibration coefficient. However, two effects can produce an inaccurate prediction. The number of induced fissions for the same fissile mass varies according to the waste matrix composition, particularly the neutron slow-down and absorption ratio. Secondly, the presence of fissile clusters can impact the neutron interrogation due to an increase in self-shielding effect. This work presents a matrix effect correction method based on the use of internal flux monitors (sensitive to the neutron absorption ratio) and the transmission signal (sensitive to the slow-down ratio). It relies on a numerical model of the whole measurement cell developed with the Monte-Carlo N-Particle transport (MCNP) code. The calibration coefficient of 72 different matrices, representative of the waste produced at La Hague, were simulated and a statistical model using a multilinear regression was then established. This simulated-based approach provides a more robust and comprehensive estimation of the residual fissile mass without impacting accuracy thanks to the flux monitors and the transmission signals.

Novel high-efficiency 2D position-sensitive ZnS:Ag/6LiF scintillator detector for neutron diffraction

Scintillator-based ZnS:Ag/6LiF neutron detectors have been under development at ISIS for more than three decades. Continuous research and development aim to improve detector capabilities, achieve better performance and meet the increasingly demanding requirements set by neutron instruments. As part of this program, a high-efficiency 2D position-sensitive scintillator detector with wavelength-shifting fibres has been developed for neutron-diffraction applications. The detector consists of a double scintillator-fibre layer to improve detection efficiency. Each layer is made up of two orthogonal fibre planes placed between two ZnS:Ag/6LiF scintillator screens. Thin reflective foils are attached to the front and back scintillators of each layer to minimize light cross-talk between layers. The detector has an active area of 192 × 192 mm with a square pixel size of 3 × 3 mm. As part of the development process of the double-layer detector, a single-layer detector was built, together with a prototype detector in which the two layers of the detector could be read out separately. Efficiency calculations and measurements of all three detectors are discussed. The novel double-layer detector has been installed and tested on the SXD diffractometer at ISIS. The detector performance is compared with the current scintillator detectors employed on SXD by studying reference crystal samples. More than a factor of 3 improvement in efficiency is achieved with the double-layer wavelength-shifting-fibre detector. Software routines for further optimizations in spatial resolution and uniformity of response have been implemented and tested for 2D detectors. The methods and results are discussed in this manuscript.

Experimental characterization of discrimination capabilities of EJ-276 and EJ-276G read by SiPM by pulse-shape analysis techniques

This work aims at the investigation of the Pulse Shape Discrimination (PSD) capabilities of two very compact detection systems composed of a 3x3x3 cm3 EJ 276 and a 3x3x3 cm3 EJ 276G (the latter green shifted version) plastic scintillators, both coupled to Silicon Photomultiplier (SiPM). The studied systems are supposed to be the basic elementary cell of a new multi-detector for simultaneous detection of neutrons and light charged particles called NArCoS (Neutron Array for Correlation Studies) having both high angular and energy resolution. In this perspective, the results of the experimental qualification of two prototypes with gamma and alpha radioactive sources and in beam tests are reported, in order to characterize the optimum choice for the new device.

Development of trench-shaped microstructure thermal neutron detector using α-Al2O3:C based on optically stimulated luminescence

Optical stimulated luminescence technique is increasingly used in neutron personal dosimetry, due to its capability of fast readout and potential for re-estimation of absorbed dose. The design configuration and performance of the microstructure optically stimulated luminescence neutron detector (MOSLND) using α-Al2O3:C was reported. To improve thermal neutron response, the MOSLND is structured with a matrix of microstructure trenches into the α-Al2O3:C substrate and backfilled with 6LiF. To obtain an optimum trench geometric parameter, several Monte Carlo simulations were performed using Geant4 code. The simulation results show that relatively high energy deposition can be realized for small cell dimensions with deep trenches, and is significantly increased compared with that of simple planar designs. Based on the results of calculation and practical limitation, the device was produced and tested using D2O-modrated 252Cf. The optimized minimal detectable dose (MDD) corresponding to signal integration time of 2 s is 7.2 μSv. The experimental results indicate that MOSLND can be a potential solution for personal neutron dosimetry.

Operation of a 250μm-thick SiC detector with DT neutrons at high temperatures

The Silicon Carbide detector (SiC) is an object of research as an alternative to diamond detectors for fast neutron detection and spectrometry where harsh environments are an issue, like in Tokamaks. Since future breeding blankets mock-ups will feature temperatures up to 550 °C, diamond detectors were characterized in the past, finding limitations in their functionality at high temperatures. This paper expands on the previous work by proving the detection of fast neutrons with good detection parameters of a 250 μm-thick 4 H-SiC detector prototype at temperatures up to 250 °C, highlighting the detector's excellent resilience to temperature. The experiment is conducted with instrumentation similar to the one used in the past with diamond detectors, using as source of irradiation the Frascati Neutron Generator (FNG) in ENEA, which is accelerator driven neutron source based on deuterium-tritium (DT) fusion reaction.

LURAD: Design study of a comprehensive radiation monitor package for the gateway and the lunar surface

Moon is an auspicious environment for the study of Galactic cosmic rays (GCR) and Solar Particle Events (SEP) due to the absence of magnetic field and atmosphere. The same characteristics raise the radiation risk for human presence in orbit around it or at the lunar surface. The secondary (albedo) radiation resulting from the interaction of the primary radiation with the lunar soil adds an extra risk factor, because neutrons are produced, but also it can be exploited to study the soil composition. In this paper, the design of a comprehensive radiation monitor package tailored to the lunar environment is presented. The detector, named LURAD, will perform spectroscopic measurements of protons, electrons, heavy ions, as well as gamma-rays, and neutrons. A microdosimetry monitor subsystem is foreseen which can provide measurements of LET(Si) spectra in a wide dynamic range of LET(Si) and flux for SPE and GCR, detection of neutrons and biological dose for radiation protection of astronauts. The LURAD design leverages on the following key enabling technologies: (a) Fully depleted Si monolithic active pixel sensors; (b) Scintillators read by silicon photomultipliers (SiPM); (c) Silicon on Insulator (SOI) microdosimetry sensors; These technologies promise miniaturization and mass reduction with state-of-the-art performance. The instrument’s design is presented, and the Monte Carlo study of the feasibility of particle identification and kinetic energy determination is discussed.

Status of h-BN quasi-bulk crystals and high efficiency neutron detectors

III-nitrides have fomented a revolution in the lighting industry and are poised to make a huge impact in the field of power electronics. In the III-nitride family, the crystal growth and use of hexagonal BN (h-BN) as an ultrawide bandgap (UWBG) semiconductor are much less developed. Bulk crystals of h-BN produced by the high-temperature/high-pressure and the metal flux solution methods possess very high crystalline and optical qualities but are impractical to serve as substrates or for device implementation as their sizes are typically in millimeters. The development of crystal growth technologies for producing thick epitaxial films (or quasi-bulk or semi-bulk crystals) in large wafer sizes with high crystalline quality is a prerequisite for utilizing h-BN as an UWBG electronic material. Compared to traditional III-nitrides, BN has another unique application as solid-state neutron detectors, which however, also require the development of quasi-bulk crystals to provide high detection efficiencies because the theoretical efficiency (ηi) relates to the detector thickness (d) by ηi=1−e−dλ, where λ denotes the thermal neutron absorption length which is 47 μm (237 μm) for 10B-enriched (natural) h-BN. We provide an overview and recent progress toward the development of h-BN quasi-bulk crystals via hydride vapor phase epitaxy (HVPE) growth and the attainment of thermal neutron detectors based on 100 μm thick 10B-enriched h-BN with a record efficiency of 60%. The thermal neutron detection efficiency was shown to enhance at elevated temperatures. Benchmarking the crystalline and optical qualities of h-BN quasi-bulk crystals with the state-of-the-art mm-sized bulk crystal flakes and 0.5 μm thick epitaxial films identified that reducing the density of native defects such as vacancies remains the most critical task for h-BN quasi-bulk crystal growth by HVPE.

Method for stabilizing the detection efficiency of grazing angle incidence boron-lined neutron detectors

Boron-lined gaseous neutron detectors intrinsically suffer from the “self-absorption” effect and hence their neutron detection efficiencies might be nonconstant, when the threshold of them undergoes unexpected variation. To address this problem, we propose a maximum likelihood estimation-based threshold determining method, via which the pulse height spectra acquired under different high voltages could be rescaled to the same abscissa axis of deposited energies. Monte Carlo simulations were conducted to study the relationship between the precision of the threshold determination and the counting statistics, as well as the energy deposition spectrum, indicating that the grazing angle incidence neutron detector can achieve a fairly small relative standard variation for a spectrum with a modest total neutron counts. A prototype grazing angle incidence neutron detector has been constructed and tested under high voltages ranging from 500 V to 950 V. The experimental results show that, with the maximum likelihood estimation-based method, the threshold's relative standard deviations are less than 10% even with a total neutron counts as low as 100. As a result, the maximum relative variance of the counting plateau curve is 4.8% in the region of [500 V, 900 V] when the detector operates at a grazing angle of 1.8°. The results presented in this study indicate that combining the grazing angle incidence and the maximum likelihood estimation-based threshold determining method would be a promising way to achieve stable neutron detection efficiency for neutron detectors with the boron layer as the neutron convertor.

Multi-Blade detector with VMM3a-ASIC-based readout: installation and commissioning at the reflectometer Amor at PSI

The Multi-Blade (MB) Boron-10-based neutron detector is the chosen technology for three instruments at the European Spallation Source (ESS): the two ESS reflectometers, ESTIA and FREIA, and the Test Beam Line. A fourth MB detector has been built, installed and commissioned for the user operation of the reflectometer Amor at PSI (Switzerland). Amor can be considered a downscaled version of the ESS reflectometer ESTIA. They are based on the same Selene guide concept, optimized for performing focusing reflectometry on small samples. The experience gained at Amor is invaluable for the future deployment of the MB detector at the ESS. This manuscript describes the MB detector construction and installation at Amor along with the readout electronics chain based on the VMM3a ASIC. The readout chain deployed at Amor is equivalent of that of the ESS, including the readout master module (RMM), event-formation-units (EFUs), Kafka, FileWriter and live visualisation tools.

Study on structural and material dependence of Rhodium Self-powered Neutron Detector performance

The neutron measurement properties of Rh-SPNDs are greatly affected by their geometric constructions, which needs to be optimized while designing. This effect is reflected in the sensitivities for gamma and neutron detection. However, the influence on gamma sensitivity has not been fully analyzed before, which is of the same importance as neutron sensitivity. Therefore, it is necessary to quantitatively analyze the relationship between detector sensitivity and geometric dimensions. The effect of Rh-SPND structural and material parameters on neutron and gamma sensitivities has been calculated and analyzed through numerical simulations. The research results show that detector sensitivities are strongly depending on the detector size and its emitter shape. Moreover, the detector response to exogenous reactor gamma can be eliminated by optimizing the detector collector size.

Development of a silicon-based thermal neutron detection system

Neutron detection systems are of increasing importance in applications from basic science to medical applications and reactors. 3He proportional counters remain the most popular choice for monitoring thermal neutrons with a detection efficiency of around 60%, however, due to 3He global shortages, a new generation of detection technologies will be required to meet the rising demand. As a result, extensive research is being conducted to investigate alternative methods of neutron detection. This work presents such a system and demonstrates its calibration and evaluation using an AmBe neutron source. The detection system involves silicon sensors coated by converter layers to make the detectors sensitive to thermal neutrons via neutron capture and measurement of the resulting secondary charged particles. The detection system is presented in two configurations, a single and a multi-layer configuration, where the latter is used to increase the total detection efficiency. In addition, the system is capable of determining coincident signals from a single neutron capture, a feature which allows background suppression and an increase in the purity of the neutron signal which is particularly useful in mixed radiation environments.

A protype of compact and high-yield DD neutron generator

Neutron generators are widely utilized in various fields, including scientific research, activation analysis, and detection of IED or drugs, due to their high neutron yield, safety, and flexibility. In this paper, we report about the development of a compact and high-yield dd neutron generator based on an Electron Cyclotron Resonance (ECR) ion source at the China Institute of Atomic Energy. The ion source to produce a high-intensity ion beam, which is used to bombard a water-cooled solid metal target. By means of the (D, D) nuclear reaction, 2.5MeV neutrons are generated. We describe the detailed design of this compact dd neutron generator and present the preliminary measurement results of its neutron yield, as measured by a calibrated 3He neutron detector. The generator has been tested for nearly 300 hours, demonstrating stable operation without any component damage. With its compact size, high yield, and long lifespan, this generator could meet the demand for a 2.5MeV neutron source in many scientific research and select industrial applications.

In-beam test results of an RPC-based module for position-sensitive neutron detectors with timing readout

Recently we have proposed a new concept of a thermal neutron detector based on resistive plate chambers and 10B4C solid neutron converters, enabling to readout with high resolution in both the 3D position of neutron capture and the neutron time of flight (ToF). In this paper, we report the results of the first beam tests conducted with a new neutron RPC detection module, coupled to the position readout units of a new design. The main focus is on the measurements of the neutron ToF and identification of the converter layer where the neutron is captured, giving the position along the beam direction.

An optimization design for fiber-optic neutron detector based on 6LiF/ZnO:Ga and wavelength shifting fibers

The fiber-optic neutron detector consists principally of a neutron-sensitive scintillator, optical fiber, and photomultiplier tube. It has features such as small size, real-time online measurement capability, and high resistance to electromagnetic interference. This detector is excellent for neutron detection in areas with limited space and strong electromagnetic interference. However, its small size results in a comparatively low neutron sensitivity. The goal of this study is to look into the relationship between detector parameters and performance in order to improve the detector design. The research begins with the development of a detector model using Monte Carlo simulation programs to investigate the relationship between the 6LiF/ZnO:Ga mass ratio, thickness, wavelength-shifting fiber length, and detector performance. The 6LiF/ZnO:Ga mass ratio was then used as the test parameter to create equivalent detector samples for experimental validation. The results show that the detector has the highest neutron sensitivity when the mass ratio of 6LiF/ZnO:Ga is 1:1. This pattern is consistent with theoretical simulation results, indicating that the optimization strategy for detector parameters is feasible. The results of this work give a theoretical foundation for the development and practical implementation of the fiber-optic neutron detector.

Vaporized purification and growth of optically transparent Trans-Stilbene for fast neutron detection applications

The paper reports the successful growth of large, crack-free trans-stilbene (TSB) single crystals using an in-house developed vertical Bridgman setup. The material purification involved a novel vaporized method at 130 °C. Parameters like furnace setup and ampoule’s cone angle were optimized during the growth process. The Powder XRD pattern confirms the phase of material and crystallinity. The crystal exhibited high transmittance (78 %) in the visible region, with an optical band gap of 3.4 eV. Photoluminescence study indicated strong blue emission at 380 nm, with radioluminescence spectroscopy showing emissions at 387 nm under X-ray radiation. The crystal exhibited a scintillation decay time of 6 ns under 137Cs gamma source, highlighting its fast decay and efficient PSD property with a figure of merit of 2.24 for fast neutron detection applications.