Muon-induced neutrons are a critical background for rare event searches in deep underground laboratories. Muon-induced Coulomb excitation, which is a significant component of this background, remains a major source of uncertainty in simulation codes such as FLUKA and Geant4. These uncertainties primarily stem from (1) an oversimplified approximation of the virtual photonuclear cross section and (2) incomplete experimental data for the real photonuclear cross section. This work proposes an alternative, cost-effective experimental method to estimate the muon-induced neutron yield originating from Coulomb excitation. Using the plane-wave Born approximation (PWBA) method, we derive an equivalence relationship between the virtual photon spectra of relativistic electrons and muons. We demonstrate an equivalence condition where the E1 virtual photon spectrum of a high-energy muon is approximately equivalent to that of an electron. This implies that the neutron cross sections via Coulomb excitation are also approximately equal: σ _( μ ,μ ^'T n) ( E_μ) ≈σ _( e,e^'T n) ( E_e) when the equivalence condition is satisfied. Consequently, the difficult-to-measure muon-induced neutron yield can be determined experimentally using accessible, high-flux relativistic electron beams. This approach provides an experimental reference that bypasses the theoretical uncertainties associated with virtual photonuclear cross sections and the reliance on incomplete real photonuclear cross-section data.

In this study, reactions induced by electrons with energies ranging from 20 to 110 MeV were investigated by measuring residual gamma-ray activities, in order to study the Coulomb excitation-induced nuclear reaction. The experiments measured cross sections for 181Ta( e, e'xn; x= 1-8 )181−xTa reactions. Notably, this study reports, for the first time, ( e,e'xn ) cross-section data for reactions with incident electrons’ energy higher than 30 MeV. Comparisons between the measured cross sections and theoretical values calculated by TALYS2.0 code revealed significant discrepancies. Possible sources of these discrepancies are discussed, including transmission coefficients as well as nuclear-level densities.

In spent nuclear fuel reprocessing, neutron poisons are usually added to the spent nuclear fuel solution for maintaining the solution in subcritical state. Gadolinium nitrate is a widely used neutron poison, and its concentration should be exactly known for spent nuclear fuel reprocessing. In this study, an e-LINAC driven photoneutron source based gadolinium concentration monitoring method is proposed to measure the gadolinium concentration by analyzing the lifetime of photoneutrons in gadolinium solutions. Monte Carlo simulation and experimental results are both presented and discussed. The results demonstrate this method works well for measuring gadolinium concentration within the range of 0.1 g/L similar to 1.0 g/L.

The grades of the minerals significantly affects the energy consumption and chemical pollution along with the beneficiation process for extracting lithium element from the ores. Based on the large neutrons’ macro cross section of the Li2O cluster inside the ores, the grades of lithium ores could be analyzed by the thermal neutron penetrating information. In this work, a bimodal imaging method, which utilizes both the information of penetrating neutrons and X-rays delivered by the same electron linear accelerator driven photoneutron system, was proposed to investigate the lithium concentration of each ore. A linearity R-square value of 0.991 between the results obtained with this method and those from the chemical method has been achieved. The average error in lithium concentration estimation is approximately 0.2 weight percent (wt%). The underlying principles and the experimental results will be elaborated on in this study.

To provide the reference neutron radiation data for the single-event effect (SEE) analysis and dose equivalent calculation, a compact and wide energy range CLYC(Ce) (Cs2LiYCl6 : Ce3+) neutron detector was designed. CLYC(Ce) scintillator has the ability to detect fast neutrons, thermal neutrons, and gamma rays simultaneously and can be used in various radiation scenes. The detector was successfully mounted on a high-altitude balloon for near-space neutron measurement, and the measured results showed that charged particles, neutrons, and gamma rays reached the maximum flux at an altitude of about 20 km, called the Regener-Pfotzer (R-P) maximum phenomenon. The neutron deposition energy spectrum measured by the detector during the balloon flight was also used to unfold the atmospheric neutron energy spectrum in the range of 0.1-100 MeV at an average altitude of 27 km. These measured results can provide references for radiation protection and single-particle effects in the near-space environment.

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 degrees . 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.

Predicting the analysis sensitivities of interested elements is one of the major concerns in various applications of neutron activation analysis (NAA). As the specific gamma-ray yield after the neutron irradiation could be affected by the irradiating neutrons' spectrum, which can hardly be constant for NAA applications of different interested elements (and matrix elements) that need their own customized optimal neutron moderators, a calculator for predicting the analysis sensitivities of NAA should be able to consider all the contributions of neutrons with different energies. In this study, a MATLAB-based code, named as CYANUS (the Calculator for Yield Analysis of NeUtron Activation) is developed to quantitatively evaluate the specific yields of delayed gamma-rays released from the neutron irradiated objects. The comparison between the results calculated by CYANUS and those from other currently available online programs demonstrates that this work shows the smallest relative error with respect to the experimentally measured results, indicating that CYANUS is promising to provide an accurate evaluation of the specific gamma-ray yields when the object is irradiated by customized neutron spectrum in the NAA applications.

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, high-quality centimeter-sized LiInP2 Se6 single crystals are developed using the Bridgman method and their structure and property characteristics are systematically investigated. 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. The primary mechanisms of Se-vacancy and InLi antisite defects in the carrier trapping process are also identified. Such insights are critical for further enhancing the energy resolution of LiInP2 Se6 bulk crystals toward the intrinsic level (≈8.6% as indicated by the 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.

Analyzing concentrations/grades for interested valuable elements in mineral ores with low detection limit, high accuracy, high precision and high assay speed is essential in the whole processing chain for economic benefits. In this work, a method using delayed gamma rays from neutron activation, based on an e-LINAC driven photoneutron source and a high-purity germanium detector, is introduced. It fulfills the requirements in analysis of gold ores including low detection limit (0.1 g/t), high precision and high assay speed (several minutes per sample for fulfilling the standard requirements). Comparing to the traditional method of fire assay, this method shows the advantages of low labor consumption, low time consuming, no toxic pollution, multi-element analysis ability and non-destruction.

The CLYC(Ce) (Cs 2 LiYCl 6 :Ce 3+ ) scintillator can identify different particles with various specific energy losses and is capable of measuring the fast neutron energy via the 35 Cl( n,p ) 35 S reaction. Thus, it is rational to expect using this detector for monitoring the on-site neutron dose rate for astronauts or equipments working at a spacecraft, which may undergo the irradiation of cosmic rays of energetic protons or alpha particles that could induce the production of spallation neutrons. However, as the spallation neutrons, as well as the moderated neutrons, have an energy distribution from the thermal region to several hundred MeV, the direct measurement of the neutron spectrum, which helps calculate the exact value of dose rate in the spacecraft, requires that the energy response matrices should be known in advance. In this study, we calibrated a Φ38 mm × 38 mm CLYC(Ce) scintillator detector with the Back-n beamline at the China Spallation Neutron Source (CSNS), acquiring its energy response matrices (ERM) ranging from 0.1 MeV to 100 MeV. To verify the CLYC(Ce) scintillator detector's capability for measuring neutrons with such a wide region, using the ERM, the energy spectrum of the Back-n beamline was reconstructed and the result conformed to the CSNS-measured result well; a good conformation between the reconstructed spectrum and the standard Watt fission neutron spectrum of 252 Cf was also observed. This calibrated detector then was used to measure the cosmic-ray induced neutron spectra at five different sites in China of various altitudes. The measured neutron fluxes at five different sites conformed to results predicted by the EXcel based Program Atmospheric Cosmic-ray Spectrum (EXPACS). The results presented in this study indicate that the CLYC(Ce) scintillator detector is promising to be used in spacecraft as a neutron monitor with a wide energy range.

A neutron beam monitor can play an important role in a neutron experiment when the spatial and temporal distribution of the incident neutrons should be exactly known. In this study, we propose a method to realize a neutron beam monitor with a thin boron layer, which is necessary for easily setting an optimal threshold to separate the neutron signals from those of gamma rays and electronic noise with the aid of atomic layer deposition (ALD) technique. By applying the B2O3 layer forming process and the ZnO layer forming process, boron layers with thicknesses ranging from 16.8 nm to 472.7 nm are successfully prepared to form the beam monitors with a multiwire proportional chamber (MWPC) as the readout. A test is conducted at the compact pulsed hadron source (CPHS) at Tsinghua University. The results show that a slope of 0.7%/100 V of the counting plateau can be achieved for the high voltage region of 250 V, with the spatial resolution being better than 3.09 mm. The B2O3 film with a minimum mass thickness of 0.38 mu g/cm2 enables a maximum neutron flux of 9.7 x 107 n/cm2/s to be monitored with this beam monitor, with an accompanying attenuation for penetrating incident neutrons of 0.35%, significantly smaller than that of typical state-of-art beam monitor.

Purpose To conduct research related to slow neutrons, fast neutrons must be mode-rated and shifted to the desired energy region. Methods In this research, an iterated prediction method, in which the neutron transportation properties of all materials were characterized by a reflection matrix, R, and a transmission matrix, T, was proposed to bypass a time-consuming Monte Carlo simulation and predict the performance of the moderator, including the epithermal neutron flux and the dose of fast neutrons and gamma rays, used for boron neutron capture therapy (BNCT). To find the optimal solution in the huge parameter space, a genetic algorithm combined with transmission and reflection matrices was utilized. Results The results showed that a 70-loop iteration was able to find a design for the moderator of BNCT with almost 80% higher epithermal neutron flux per kilowatt than that of the empirically optimized moderator that was previously reported in the literature. Compared with the Monte Carlo method, this method had the advantage of reducing the calculation time and statistical errors. Conclusion The genetic algorithm with matrices (GAM) method can be used to find an optimal solution in a huge parameter space without brute-force calculations. It could be a promising method for designing the moderator for thermal or epithermal neutron usages.

Low energy accelerator driven neutron sources are promising candidates to obtain a neutron yield as high as 1014 n/s, which is required for a variety of applications, such as boron neutron capture therapy, neutron imaging, and neutron scattering. The methods to generate neutrons can be divided into two categories: hadron-based and photon-based methods. In order to better understand which kind of source would be the better choice for delivering a brilliant neutron beam robustly, in this paper, the underlying principles of neutron production, as well as the simulation results of neutron yield, target heat dissipation, thermal stress, and reaction byproducts concentration of these two types of neutron sources, will be elaborated on. A preliminary photoneutron target station design based on a 50 MeV/50 kW electron linear accelerator, including the optimized neutron yield, thermal hydraulic analysis, and shielding calculation, is presented as well to demonstrate the method to deliver brilliant thermal neutron beam of 1.03 × 1010 cm−2 s−1 sr−1.

Developing small-angle neutron scattering techniques at compact accelerator-driven neutron sources (CANS) is of great importance for expanding the user community and advancing CANS capability. At the Compact Pulsed Hadron Source (CPHS) at Tsinghua University, neutron-focusing mirrors are under intensive research to address the challenge. A grazing-incidence focusing SANS (gif-SANS) project is initialized. It employs a nested supermirror assembly with a large collecting area to achieve ⩾ 10 5 n/s neutron intensity at Q min ⩽ 0.007 Å − 1 . It will equip two detectors, one being a 3He detector for normal Q-range measurements, and the other being a high-resolution detector for extending the Q min down to 10 − 3 Å − 1 . In this work, we present the conceptual design of the gif-SANS at CPHS. Such a scheme is conducive to enable high-performance SANS measurements at CANS.

A method for A method for evaluating the grade of uranium (U) ores through the analysis of beta-delayed neutrons following (gamma, fission) is discussed. By measuring beta-delayed fission neutrons stimulated from U-238, the U-Ra disequilibrium problem, which limits the accuracy of traditional grade estimation methods that rely on measuring radioactivity, is addressed. In this research, 6 MV bremsstrahlung photons, delivered by a 6 MeV electron linear accelerator (e-LINAC), were used to irradiate U ore samples, and a moderator surrounded thermal neutron detector was designed to register the emitted neutrons after each X-ray pulse. Although the prompt fission neutrons were discarded due to the interference caused by the photoneutrons emitted from the matrix nuclides in the analytical environment, an excellent linear relationship was observed between the counts of beta-delayed neutrons and U ore grades, demonstrating that this method is promising for the in-situ analysis of U ores.

Both X-ray imaging and neutron imaging are essential methods in non-destructive testing. In this work, a bimodal imaging method combining neutron and X-ray imaging is introduced. The experiment is based on a small electron accelerator-based photoneutron source that can simultaneously generate the following two kinds of radiations: X-ray and neutron. This identification method utilizes the attenuation difference of the two rays’ incidence on the same material to determine the material’s properties based on dual-imaging fusion. It can enhance the identification of the materials from single ray imaging and has the potential for widespread use in on-site, non-destructive testing where metallic materials and non-metallic materials are mixed.

Small Angle Neutron Scattering (SANS) measures the angular distribution of neutrons scattered by the sample to calculate the momentum transfer in the scattering process. However, the incident neutrons may firstly undergo unwanted collisions with the detector's structural material before they are registered. The detection of such spurious neutrons might lead to a biased interpretation to the microstructure of the inspected sample. A newly-designed boron-lined honeycomb converter based gaseous neutron detector is introduced in this study to provide a capability for suppressing the spurious neutrons. The simulation and experimental results indicate that a 3 to 10 times improvement for the spurious neutron suppression capability could be achieved.

空间中子是影响航天器和航天员安全的重要辐射要素之一。优化中子探测器,提高测量效率,提升反演精度是中子测量的难点。中国空间站将搭载一种基于新型中子探测材料Cs2LiYCl6∶Ce（CLYC）闪烁体的中子探测器,该探测器具有同时测量热中子和快中子,以及探测效率高等特点。针对该新型探测器的中子能谱反演,分析了不同能量中子在该探测器中的响应特点,分析了中子反演常用的概率迭代法和非负最小二乘（NNLS）法的优缺点,考虑到这2种方法在CLYC探测器反演应用中的不足,提出了基于增广矩阵的非负最小二乘（AM-NNLS）法。数值实验结果表明:AM-NNLS法具有反演运算效率高和反演相对误差小的特点,验证了所提方法的有效性。

Self-powered neutron detectors (SPND) play a key role in the monitoring of the neutron flux in the reactor core. In this research, a modified simulation method is proposed and realized in order to predict the performance of the SNPD that might be affected by a variety of parameters of the detector. Compared with the methods proposed by researchers in the past, this method involves more comprehensive physical processes, and it can be used to analyze the sensitivity and life-span of a practical detector under real reactor conditions. The research results are compared with the experimental results and show a relative error < 4%, better than the relative error of > 9% of past research.

A thermal neutron detector design with a boron-lined honeycomb as the neutron converter was proposed, which can be probably a He-3 alternative detector used in neutron scattering. This detector demands a high uniformity drift electric field due to the electron migration process, which simplifies the detector structure and improves the detector robustness. To research the influencing parameters to the drift electric field, the Garfield 9 and Maxwell 11 simulations were carried out. The simulation results demonstrated that both the field-cage pitch and the width of field strips determined the uniformity of drift electric field. The field-cage with optimized structure for the boron-lined honeycomb neutron detector was also designed, with 2 mm pitch, 1.5 mm width of inner field strip and 0.5 mm width of outer mirror field strip. The result of neutron experiment shows an electron migration efficiency increase of 12.4% and a neutron detection efficiency increase of 26%, demonstrating the effectiveness of field-cage optimization and drift electric field uniformity promotion.