Simulation of GaN micro-structured neutron detectors for improving electrical properties

Nowadays,the superior detection performance of semiconductor neutron detectors is a challenging task.In this paper,we deal with a novel GaN micro-structured neutron detector(GaN-MSND)and compare three different methods such as the method of modulating the trench depth,the method of introducing dielectric layer and p-type inversion region to improve the width of depletion region(W).It is observed that the intensity of electric field can be modulated by scaling the trench depth.On the other hand,the electron blocking region is formed in the detector enveloped with a dielectric layer.Furthermore,the introducing of p-type inversion region produces new p/n junction,which not only promotes the further expansion of the depletion region but also reduces the intensity of electric field produced by main junction.It can be realized that all these methods can considerably enhance the working voltage as well as W.Of them,the improvement on W of GaN-MSND with the p-type inversion region is the most significant and the value of W could reach 12.8μm when the carrier concentration of p-type inversion region is 10^17 cm^-3.Consequently,the value of W is observed to improve 200%for the designed GaN-MSND as compared with that without additional design.This work ensures to the researchers and scientific community the fabrication of GaN-MSND having superior detection limit in the field of intense radiation.

Study on the gamma rays and neutrons energy response optimization of a scintillating fiber detector for EAST with Geant4

A new scintillating fiber detector inside magnetic shielding tube was designed and assembled for use in the next round of fusion experiments in the experimental advanced superconducting tokamak to provide D–T neutron yield with time resolution.In this study,Geant4 simulations were used to obtain the pulse height spectra for ideal signals produced when detecting neutrons and gamma rays of multiple energies.One of the main sources of interference was found to be low-energy neutrons below 10–5 MeV,which can generate numerous secondary particles in the detector components,such as the magnetic shielding tube,leading to high-amplitude output signals.To address this issue,a compact thermal neutron shield containing a 1-mm Cd layer outside the magnetic shielding tube and a 5-mm inner Pb layer was specifically designed.Adverse effects on the measurement of fast neutrons and the shielding effect on gamma rays were considered.This can suppress the height of the signals caused by thermal neutrons to a level below the height corresponding to neutrons above 4 MeV because the yield of the latter is used for detector calibration.In addition,the detector has relatively flat sensitivity curves in the fast neutron region,with the intrinsic detection efficiencies(IDEs)of approximately 40%.For gamma rays with energies that are not too high(<8 MeV),the IDEs of the detector are only approximately 20%,whereas for gamma rays below 1 MeV,the response curve cuts off earlier in the low-energy region,which is beneficial for avoiding counting saturation and signal accumulation.

Fabrication of a single-crystal diamond neutron detector and its application in 14.1 MeV neutron detection in deuterium-tritium fusion experiments

A single-crystal diamond detector is fabricated to diagnose 14.1 MeV deuterium-tritium(D-T)fusion neutrons.The size of its diamond film is 4.5 mm×4.5 mm×500μm.This film is sandwiched by a flat,strip-patterned gold electrode.The dark current of this detector is experimentally measured to be lower than 0.1 nA under an electric field of 30 kV cm^(-1).This diamond detector is used to measure D-T fusion neutrons with a flux of about 7.5×10^(5) s^(-1)cm^(-2).The pronounced peak with a central energy of 8.28 MeV characterizing the^(12)C(n,α)~9Be reaction in the neutron energy spectrum is experimentally diagnosed,and the energy resolution is better than 1.69%,which is the best result reported so far using a diamond detector.A clear peak with a central energy of 6.52 MeV characterizing the^(12)C(n,n')3αreaction is also identified with an energy resolution of better than 7.67%.

Twin model-based fault detection and tolerance approach for in-core self-powered neutron detectors

The in-core self-powered neutron detector(SPND)acts as a key measuring device for the monitoring of parameters and evaluation of the operating conditions of nuclear reactors.Prompt detection and tolerance of faulty SPNDs are indispensable for reliable reactor management.To completely extract the correlated state information of SPNDs,we constructed a twin model based on a generalized regression neural network(GRNN)that represents the common relationships among overall signals.Faulty SPNDs were determined because of the functional concordance of the twin model and real monitoring sys-tems,which calculated the error probability distribution between the model outputs and real values.Fault detection follows a tolerance phase to reinforce the stability of the twin model in the case of massive failures.A weighted K-nearest neighbor model was employed to reasonably reconstruct the values of the faulty signals and guarantee data purity.The experimental evaluation of the proposed method showed promising results,with excellent output consistency and high detection accuracy for both single-and multiple-point faulty SPNDs.For unexpected excessive failures,the proposed tolerance approach can efficiently repair fault behaviors and enhance the prediction performance of the twin model.

Silicon photomultiplier based scintillator thermal neutron detector for China Spallation Neutron Source(CSNS)

The energy-resolved neutron imaging spectrometer(ERNI)will be installed in 2022 according to the spectrometer construction plan of the China Spallation Neutron Source(CSNS).The instrument requires neutron detectors with the coverage area of approximately 4 m^(2)in 5°-170°neutron diffraction angle.The neutron detection efficiency needs to be better than 40%at 1 A neutron wavelength.The spatial resolution should be better than 3 mm×50 mm in the horizontal and vertical directions respectively.We develop a one-dimensional scintillator neutron detector which is composed of the^(6)Li F/Zn S(Ag)scintillation screens,the wavelength-shifting fiber(WLSF)array,the silicon photomultipliers(Si PMs),and the self-designed application-specific integrated circuit(ASIC)readout electronics.The pixel size of the detector is designed as 3 mm×50 mm,and the neutron-sensitive area is 50 mm×200 mm.The performance of the detector prototype is measured using neutron beam 20#of the CSNS.The maximum counting rate of 247 k Hz,and the detection efficiency of63%at 1.59 A are obtained.The test results show that the performance of the detector fulfills the physical requirements of the ERNI under construction at the CSNS.

Performance optimization of scintillator neutron detectors for EMD in CSNS

Chinese Spallation Neutron Source(CSNS) has successfully produced its first neutron beam in 28th August 2017. It has been running steadily from March, 2018. According to the construction plan, the engineering materials diffractometer(EMD) will be installed between 2019–2023. This instrument requires the neutron detectors with the cover area near3 m2in two 90° neutron diffraction angle positions, the neutron detecting efficiency is better than 40%@1A, and the spatial resolution is better than 4 mm×200 mm in horizontal and vertical directions respectively. We have developed a onedimensional position-sensitive neutron detector based on the oblique6Li F/Zn S(Ag) scintillators, wavelength shifting fibers,and Si PMs(silicon photomultipliers) readout. The inhomogeneity of the neutron detection efficiency between each pixel and each detector module, which caused by the inconsistency of the wave-length shifting fibers in collecting scintillation photons, needs to be mitigated before the installation. A performance optimization experiment of the detector modules was carried out on the BL20(beam line 20) of CSNS. Using water sample, the neutron beam with Φ5 mm exit hole was dispersed related evenly into the forward space. According to the neutron counts of each pixel of the detector module, the readout electronics threshold of each pixel is adjusted. Compared with the unadjusted detector module, the inhomogeneity of the detection efficiency for the adjusted one has been improved from 69% to 90%. The test result of the diffraction peak of the standard sample Si showed that the adjusted detector module works well.

Investigation of enhancement in planar fast neutron detector efficiency with stacked structure using Geant4

Geant4 based Monte Carlo study has been carried out to assess the improvement in efficiency of the planar structure of Silicon Carbide(SiC)-based semiconductor fast neutron detector with the stacked structure. A proton recoil detector was simulated, which consists of hydrogenous converter, i.e., high-density polyethylene(HDPE) for generating recoil protons by means of neutron elastic scattering(n, p) reaction and semiconductor material SiC, for generating a detectable electrical signal upon transport of recoil protons through it. SiC is considered in order to overcome the various factors associated with conventional Si-based devices such as operability in a harsh radiation environment, as often encountered in nuclear facilities. Converter layer thickness is optimized by considering 10~9 neutron events of different monoenergetic neutron sources as well as ^(241)Am-Be neutron spectrum. It is found that the optimized thickness for neutron energy range of 1–10 MeV is ~400 μm. However, the efficiency of fast neutron detection is estimated to be only 0.112%,which is considered very low for meaningful and reliable detection of neutrons. To overcome this problem, a stacked juxtaposition of converter layer between SiC layers has been analyzed in order to achieve high efficiency. It is noted that a tenfold efficiency improvement has been obtained—1.04% for 10 layers stacked configuration vis-à-vis 0.112% of single converter layer detector. Further simulation of the stacked detector with respect to variable converter thickness has been performed to achieve the efficiency as high as ~3.85% with up to 50 stacks.

Time Dependent DD Neutrons Measurement Using a Single Crystal Chemical Vapor Deposition Diamond Detector on EAST

a single crystal chemical vapor deposition （scCVD） diamond detector has been successfully employed for neutron measurements in the EAST （Experimental Advanced Superconducting Tokamak） plasmas. The seCVD diamond detector coated with a 5 μm 6LiF （95% 6Li enriched） layer was placed inside a polyethylene moderator to enhance the detection efficiency. The time-dependent neutron emission from deuteron plasmas during neutral beam injection （NBI） heating was obtained. The measured results are compared with that of fission chamber detectors, which always act as standard neutron flux monitors. The scCVD diamond detector exhibits good reliability, stability and the capability to withstand harsh radiation environments despite its low detection efficiency due to the small active volume.

Simulation of Suppression of Gamma Sensitivity of 'Fission Electron-Collection' Neutron Detector

The fission electron-collection neutron detector （FECND） is a current-type neutron detector. Based on the analysis of the generation process of the gamma signals of the FECND, a mechanism utilizing symmetrical structure is proposed and discussed to suppress the gamma signals. According to this mechanism, tile electrons generated from the gamma rays can be well compensated for by the adjustment of the electrodes＇ thickness and distance. In this study, based on the Monte-Carlo simulation of the gamma signals of the FECND, the varying patterns are obtained between the gamma signals and the detector parameter settings. As indicated by the simulation results, the gamma electrons can be compensated for completely by simply adjusting the coated electrode substrate thickness and distance. Moreover, with a proposed optimal parameter setting, the gamma sensitivity can be as low as 3.39×10-23 C.cm2, while the signal-to-noise ratio can be higher than 200：1. The compensation results of the γ-rays in the FECND will be slightly affected by the manufacturing error or the assembly error.

Development of a low-background neutron detector array

A low-background neutron detector array was developed to measure the cross section of the ^(13)C(a,n)^(16)O reaction,which is the neutron source for the s-process in AGB stars,in the Gamow window(E_(c.m.)=190±40 keV)at the China Jinping Underground Laboratory(CJPL).The detector array consists of 24^(3)He proportional counters embedded in a polyethylene cube.Owing to the deep underground location and a borated polyethylene shield around the detector array,a low background of 4.5(2)/h was achieved.The ^(51)V(p,n)^(51)Cr reaction was used to determine the neutron detection efficiency of the array for neutrons with energies E_(n)<1 MeV.Geant4 simulations are shown to effectively reproduce the experimental results.They were used to extrapolate the detection efficiency to higher energies for neutrons emitted in the ^(13)C(α,n)^(16)O reaction.The theoretical angular distributions of the ^(13)C(α,n)^(16)O reaction were shown to be important in the estimation of the uncertainties of the detection efficiency.

Calibration and performance of the neutron detector onboard of the DAMPE mission

The DArk Matter Particle Explorer(DAMPE),one of the four space-based scientific missions within the framework of the Strategic Pioneer Program on Space Science of the Chinese Academy of Sciences,was successfully launched on 2015 Dec.17 from Jiuquan launch center.One of the most important scientific goals of DAMPE is to search for evidence of dark matter indirectly by measuring the spectrum of high energy cosmic-ray electrons.The neutron detector,one of the four sub-payloads of DAMPE,is designed to distinguish high energy electrons from hadron background by measuring the secondary neutrons produced in the shower.In this paper,a comprehensive introduction of the neutron detector is presented,including the design,calibration and performance.The analysis with simulated data and flight data indicates a powerful proton rejection capability of the neutron detector,which plays an essential role for TeV electron identification of DAMPE.

Analysis of Nuclear Track Parameters of CN-85 Detector Irradiated to Thermal Neutrons by Using MATLAB Program

CN-85 detector which covered with boric acid H3Bo3 pellete has been irradiated by thermal neutrons from (241Am-9Be) source with activity 12 Ci and neutron flux 105 n. cm-2. s-1. The irradiation times-TD for detector were 4 h, 8 h, 16 h and 24 h. The track detector has been etched with sodium hydroxide. After chemical etching of the irradiated CN-85 detector, the images have been taken from a digital camera connected to the optical microscope. Image processing for the output images has been performed using MATALB program, and these images were analyzed and we had found the following relations: a) The relation between summation of opened track or surface density for tracks (intensity-IT) varies with radius of opening (track radius-RT). b) The relation between the tracks number-NT varies with the tracks diameter-DT (in micrometer) and tracks area-AT. That analysis of image processing was obtained, and the track intensity-IT was decreased with increase of track radius-RT at all of the irradiation time-TD. And the track intensity-IT was increased with increasing irradiation time-TD (h) for different track radius-RT (0.4225, 0.845, 1.2675 and 1.69 μm). The study indicates the possibility of using the analysis of image processing to CN-85 detector for classification of α-particle emitters through limitation of radius of track-RT, in addition to the contribution of these techniques in preparation of nano-filters and nono-membrane in nanotechnology fields.

Experimental test of a new neutron threshold detector and its application

The possibility of using 209Bi as a new threshold detector to measurc high-energy neutrons was investigated for the first time. At the same time the experiment measured successfully the emitted neutron fiuence rate, energy spectrum and dose equivalent rate distributions in the heavy ion target area using a detector complex including 209Bi, 115In, 27A1, 19F and 12C samples.

A stopping layer concept to improve the spatial resolution of gas-electron-multiplier neutron detector

In recent years,gas electron multiplier(GEM)neutron detectors have been developing towards high spatial resolution and high dynamic counting range.We propose a novel concept of an Al stopping layer to enable the detector to achieve sub-millimeter(sub-mm)spatial resolution.The neutron conversion layer is coated with the Al stopping layer to limit the emission angle of ions into the drift region.The short track projection of ions is obtained on the signal readout board,and the detector would get good spatial resolution.The spatial resolutions of the GEM neutron detector with the Al stopping layer are simulated and optimized based on Geant4 Garfield Interface.The spatial resolution of the detector is 0.76 mm and the thermal neutron detection efficiency is about 0.01%when the Al stopping layer is 3.0μm thick,the drift region is 2 mm thick,the strip pitch is 600μm,and the digital readout is employed.Thus,the GEM neutron detector with a simple detector structure and a fast readout mode is developed to obtain a high spatial resolution and high dynamic counting range.It could be used for the direct measurement of a high-flux neutron beam,such as Bragg transmission imaging,very small-angle scattering neutron detection and neutron beam diagnostic.

Fabrication and performance evaluation of GaN thermal neutron detectors with bm^6LiF conversion

A GaN-based pin neutron detector with a 6LiF conversion layer was fabricated, and can be used to detect thermal neutrons. Measurement of the electrical characteristic of the GaN-based pin neutron detector showed that the reverse leakage current of the neutron detector was reduced significantly after deposition of a 6LiF conversion layer on the detector surface. The thermal neutrons used in this experiment were obtained from an 241Am-Be fast neutron source after being moderated by 100-mm-thick high-density polyethylene. The experimental results show that the detector with 16.9-μm thick 6LiF achieved a maximum neutron detection efficiency of 1.9% at a reverse bias of 0 V, which is less than the theoretical detection efficiency of 4.1% calculated for our GaN neutron detectors.

Determination the Effect of Gamma Radiation and Thermal Neutron on PM-355 Detector by Using FTIR Spectroscopy

The effect of gamma on nuclear track detector type PM-355 (at the dose range 200 to 1600 kGy) and thermal neutron (flux 105 n·cm-2·s-1) was calculated by using of two irradiation methods. First method (G + N) was an irradiation PM-355 detector by gamma radiation and then irradiation by thermal neutrons, and another method (N + G) was irradiated by thermal neutrons and then gamma radiation. FTIR-spectroscopy was used to measure the change in deferent of transmission percent ΔT% at the wavenumber 1260 cm-1 with wavenumber 2962 cm-1 [ΔT%]1260-2962 and wavenumber 1138 cm-1 [ΔT%]1260-1138. The values of [ΔT%]1260-2962 and [ΔT%]1260-1138 were increasing with the increase of gamma irradiation with maximum response at 820 kGy and then drop after this dose until to 1600 kGy. This study determined the linear equations relation between the effect of gamma radiation on PM-355 detector and the change of [ΔT%]1260-2962 and [ΔT%]1260-1138, and this change appeared in (N + G) irradiation method better than in (G + N) irradiation method. The appearance of wavenumber 2964 cm-1 in (G + N) irradiation method referred to alkyl asymmetry C-H bond stretched out of skelated plane after changes in chemical structure of PM-355 detector by gamma or neutrons radiation.

Comparison of Experiment and Simulation of the triple GEM-Based Fast Neutron Detector

A detector for fast neutrons based on a 10 × 10 cm^2 triple gas electron multiplier （GEM） device is developed and tested. A neutron converter, which is a high density polyethylene （HDPE） layer, is combined with the triple GEM detector cathode and placed inside the detector, in the path of the incident neutrons. The detector is tested by obtaining the energy deposition spectrum with an Am Be neutron source in the Institute of Modern Physics （IMP） at Lanzhou. In the present work we report the results of the tests and compare them with those of simulations. The transport of fast neutrons and their interactions with the different materials in the detector are simulated with the GEANT4 code, to understand the experimental results. The detector displays a clear response to the incident fast neutrons. However, an unexpected disagreement in the energy dependence of the response between the simulated and measured spectra is observed. The neutron sources used in our simulation include deuterium-tritium （DT, 14 MeV）, deuterium-deuterium （DD, 2.45 MeV）, and Am Be sources. The simulation results also show that among the secondary particles generated by the incident neutron, the main contributions to the total energy deposition are from recoil protons induced in hydrogen-rich HDPE or Kapton （GEM material）, and activation photons induced by neutron interaction with Ar atoms. Their contributions account for 90% of the total energy deposition. In addition, the dependence of neutron deposited energy spectrum on the composition of the gas mixture is presented.

Sensitivity of a new-developed neutron detector

We develop a kind of neutron detector, which consists of a polyethylene thin film and two PIN semicon- ductors connected face-to-face. The detector is insensitive to γ-rays. Its sensitivity to neutron has been calculated with MCNP program and calibrated by experiments, and the results indicate that the neutron sensitivity of the compensa- tion detector will vary with polyethylene converter. The compensation PIN detector can be employed to measure pulse neutron in neutron and gamma mixture radiation field.

Large area^(3)He tube array detector with modular design for multi‑physics instrument at CSNS

The multi-physics instrument(MPI)is the first user cooperative instrument at the China Spallation Neutron Source(CSNS).It was designed to explore the structures of complex materials at multiple scales based on the neutron total scattering technique.This imposes the requirements for the detector,including a high detection efficiency to reduce the measurement time and a large solid angle coverage to cover a wide range of momentum transfers.To satisfy these demands,a large-area array of 3He-filled linear position-sensitive detectors(LPSDs)was constructed,each with a diameter of 1 inch and pressure of 20 atm.It uses an orbicular layout of the detector and an eight-pack module design for the arrangement of 3He LPSDs,covering a range of scattering angles from 3°to 170°with a total detector area of approximately 7 m2.The detector works in air,which is separated from the vacuum environment to facilitate installation and maintenance.The characteristics of the MPI detector were investigated through Monte Carlo(MC)simulations using Geant4 and experimental measurements.The results suggest that the detectors are highly efficient in the wavelength range of the MPI,and an efficiency over 25%is achievable for above 0.1 A neutrons.A minimal position resolution of 6.4 mm full width at half maximum(FWHM)along the tube length was achieved at a working voltage of 2200 V,and a deviation below 2 mm between the real and measured positions was attained in the beam experiment.The detector module exhibited good consistency and an excellent counting rate capacity of up to 80 kHz,which satisfied the requirements of experiments with a high event rate.Observations of its operation over the past year have shown that the detector works steadily in sample experiments,which allows the MPI to serve the user program successfully.

一种基于硅传感器的空间中子探测器设计

针对空间站轨道复杂的中子辐射环境,设计一种中子探测器,采用硅层叠结构,利用核反冲法及核反应法进行中子的间接探测,获取空间站轨道中子辐射的能谱信息。该中子探测器的探测范围指标为0.025 eV~10MeV,搭载于天宫空间站梦天实验舱的空间辐射生物学暴露实验装置上,用于监测空间站低地球轨道的中子辐射环境,获取在轨探测数据,可为研究空间中子对生物体造成辐射效应的作用机理提供重要依据,也可为研究次级粒子对航天器电子元件造成的单粒子效应提供必要的空间环境参数。