BackgroundUltra-high dose rate (UHDR) radiation of electron or proton beam has been shown to spare normal tissues surrounding the tumors while killing tumor cells effectively which is called the FLASH effect (FE). However, the internal mechanisms of FE has not yet been fully revealed, and the optimal parameter range for its use remains unknown.PurposeThis study aims to design an UHDR cell irradiation experimental platform that provides a stable, appropriate and wide range of adjustable dose and average dose rates for exploring the FE dependence on total dose.MethodsBased on a 7 MeV medical proton linear injector, a single scattering nozzle was designed and optimized using the Monte Carlo code FLUKA. A 40-μm-thick tantalum foil, acting as both a vacuum window and a scatterer, was comprised in the nozzle with a source-to-surface distance of 26 cm. Finally, a single pulsed shoot-through UHDR cell penetration irradiation experiment was conducted by simulation using optimized parameters for this platform.ResultsThe simulation results demonstrate that the experimental platform can provide a 2 cm diameter irradiation field with a dose homogeneity of 4.9%. By adjusting the beam intensities (0.1~1 mA) and pulse widths (20~200 μs) of proton beam pulses, the dose and corresponding average dose rate of this platform can be adjusted within the range of 6~667 Gy and 3.3×105~3.3×106 Gy·s-1, respectively. Results of simulated UHDR cell irradiation experiment show that the monolayer cells can be irradiated using a single pulsed shoot-through mode with a dose rate of 3.3×105 Gy·s-1 and doses ranging from 7~40 Gy.ConclusionThis platform enables UHDR experiments to explore the FE dependence on total dose, providing further experimental data for clarifying the FE mechanisms.

BackgroundRadio Frequency Quadrupoles (RFQs) are applied widely in proton accelerator facilities. The development of the high-frequency RFQs enables the construction of compact proton accelerator facilities, but faces with more tuning difficulties. The traditional tuning methods based on the theoretical characteristics of the RFQ cannot achieve good results with compact proton accelerators. The tuning method based on the response matrix and SVD method meets the problem of the solution being out of the range that tuners can reach.PurposeThis study aims to purpose a novel tuning method for efficient reduction of dipole components by a transform of the tuning method, so as to tune the compact RFQs better and limit the range of the solution.MethodsFirstly, a tuning method based on the response matrix and the least squares method was designed and implemented. The solution was limited, and a different weight was assigned to the dipole components for diminution during the tuning progress. Then, the tuning method was experimentally tested in the simulation environment on the aluminum RFQ prototype for verification. Both tuning with single tuner and multiple tuners were tested in simulation.ResultsVerification results show that high precision is achieved and the solution is within the expected range even without limitation. Experimental results of verification on the aluminum RFQ prototype show that the quadrupole and dipole component errors are 1.57% and 24.09%, respectively, in the initial state, but reduce to 1.39% and 2.33%, respectively, after five rounds of tuning.ConclusionsThe novel tuning method based on response matrix is verified by this study for its validity of limiting the range of the solution and reducing the dipole components efficiently, hence can be applied to RFQs operating at other frequencies as well. It can contribute to the development of compact proton accelerators and promote medical proton facilities in the future.

BackgroundAlthough the neutron image conversion screen is a key component of thermal neutron radiograph, its parameters can severely affect both the spatial resolution and thermal neutron-photon conversion efficiency.PurposeThis study aims to design a neutron image conversion screen for a thermal neutron transmission imaging system based on a compact D-D neutron source.MethodsFirstly, the Geant4 (Geometry and Tracking) program was used to simulate the physical process of thermal neutron transmission imaging and two-dimensional images of transmitted photons, and establish a thermal neutron radiography model based on LiF(ZnS) and LiF(GOS) image conversion screens, and the Siemens star image indicator model. Then, the line spread function (LSF) was employed to calculate spatial position resolution of neutron transmission imaging, and the relationships between the thickness of thermal neutron image conversion screens and the spatial resolution, as well as that between the thickness of thermal neutron image conversion screens and neutron-photon conversion efficiency were evaluated and calculated. Finally, based on parameters of thermal neutron radiography imaging system based on compact D-D neutron source at Lanzhou University, recommended thicknesses for LiF(ZnS) and LiF(GOS) conversion screens were applied to the spatial resolution test experiments.ResultsThe recommended thicknesses for LiF(GOS) and LiF(ZnS) image conversion screens are 40 μm and 80 μm, respectively, the spatial resolution of the thermal neutron radiography reach 45 and 63 μm, respectively, and the neutron-photon conversion efficiencies are 136.34 and 126.81, respectively.ConclusionsThis study lays the technical basis for the development of a thermal neutron radiography based on compact D-D neutron sources. It may be also applicable to other thermal neutron imaging systems.

BackgroundThe Energy Resolved Neutron Imaging Spectrometer (ERNI) of China Spallation Neutron Source (CSNS) is in process of building, whose diffraction detector with ninety degree partition adopts 6LiF/ZnS neutron scintillator detector with a 90° partition as its detection equipment.PurposeThis study aims to develop the readout electronics for high position resolution neutron scintillator detector of ERNI.MethodsFirstly, a capacitive network combined with center-of-gravity of the induced charge distribution was adopted for the design of readout electronics. Then, a prototype of the readout electronics system consisted of three parts: capacitive network circuit, preamplifier board and digital readout board, was developed. After functional verification, the relevant performance parameters of the developed prototype were experimentally tested in the laboratory and in the No.20 beam line of CSNS.ResultsThe experimental results show that the integration nonlinearity of electronics is better than 0.95%, the time resolution is about 12 ns, the position resolution is 1mm, and the detection efficiency is 65%@1.6 ?.ConclusionsThe prototype meets the design specifications of the project. The successful development of the prototype provides a reliable technical support for the smooth development of the spectrometer experiment in ERNI of CSNS in the future.

BackgroundThe calibration of radon measuring instruments is the most important and key technical link to ensure the reliability and accuracy of radon observation data and plays a vital role in seismic monitoring and prediction.PurposeThis study aims to obtain a calibration method suitable for the calibration of newly connected seismic water radon monitor according to the National Metrological Verification Regulations for Radon Meters (JJG825-2013), the calibration experiment is carried out for the analog radon observatory (manual), which is newly adopted by the seismic network, and the calibration method suitable for the seismic water radon observation is obtained.MethodsFirstly, the FD-125 radon-thorium analyzer was used as the experimental instrument, the calibration experiments were carried out in the standard radon chamber by three calibration methods: circulation method, vacuum method, and flow-gas method. Then, the volume response coefficients of three methods were calculated, and the uncertainty sources and mathematical models were analyzed according to JJG825—2013 regulation. Measured values by internationally recognized standard AlphaGUARDPQ2000Pro radon meter were taken as theoretical references of radon concentration for radon chambers, hence the uncertainties of three calibration methods were obtained.ResultsThe results show that the circulation calibration method has the highest detection efficiency and fewer influencing factors, and is suitable for manual and digital radon detector calibration. The vacuum calibration method is affected by the standard radon gas diluted by pipeline gas and pressure balance, resulting in low negative pressure sampling efficiency and high volume activity response coefficient R. As for the flow-gas calibration method, the continuous injecting of radon gas into the scintillation chamber affects the dynamic stability of radon gas in the scintillation chamber, and radon gas is not discharged to the background during calibration, resulting in the high volume activity response coefficient R and high intrinsic error.ConclusionsThe cyclic method is more suitable for the calibration of new seismic water radon observatories, and this study provides a reference for the calibration of other new water radon observatories and gas radon observatories.

BackgroundNuclear reactions have been crucial in the evolution of the universe since the big bang. The cross section of nuclear reaction that occurs during the early evolution of the star is extremely low, so it cannot be accurately measured in a ground laboratory. The China Jinping Underground Laboratory (CJPL), which is the deepest operational underground laboratory in the world, offers unique ultra-low background conditions that facilitate the direct evaluation of the nuclear reactions occurring during the early evolution of stars.PurposeAsymptotic giant branch (AGB) stars are thought to be the major contributor to Galactic fluorine production. However, the astronomical fluorine overabundance cannot be explained by using the current standard AGB models. Direct measurements of 19F(p,αγ)16O reactions can help solve this problem.MethodsExperiments were conducted on a high-current 400-kV JUNA (Jinping Underground laboratory for Nuclear Astrophysics) accelerator at the CJPL. A 4π BGO detector array was specially designed for the JUNA project.ResultsThe astrophysical S factors in the energy region of 72.4~188.8 keV were experimentally derived for the first time, covering the astrophysical Gamow window. The thermonuclear 19F(p,αγ)16O rate was determined at a low temperature of about 0.05 GK for astrophysical modeling. The present low-energy S factors significantly deviated from previous theoretical predictions, and the associated uncertainties were considerably reduced.

BackgroundGallium nitride (GaN) power devices have garnered attention in the anti-irradiation field owing to their excellent performance.PurposeThis study aims to explore the anti-γ-ray damage ability of gallium nitride power devices and clarify the mechanism of radiation degradation.MethodsFirstly, the domestically produced commercial NP20G65D6 P-GaN gate enhanced AlGaN/GaN High Electron Mobility Transistor (HEMT) device was taken as test sample. Then, 60Co γ-ray source with different irradiation doses of 0.3 Mrad (Si), 0.6 Mrad (Si), and 1.0 Mrad (Si), respectively, was employed to conduct total dose irradiation experiments under different bias (ON-state, OFF-state, and GND-state) conditions and annealing tests at different temperatures for enhanced AlGaN/GaN HEMT devices. Finally, the response law between the electrical performance of the device and the bias condition and annealing environment were analyzed to reveal the degradation mechanism of device sensitive parameters.ResultsThe results indicate that as the γ-ray irradiation dose increases, the device's threshold voltage exhibits a negative drift, and the transconductance peak, saturation leakage current, and reverse gate leakage current gradually increase. Simultaneously, the electrical characteristics of the device deteriorate more rapidly under the ON-state bias condition. Furthermore, annealing at high temperatures leads to a more apparent recovery of the electrical properties of devices. The analysis demonstrates that the higher the γ-ray irradiation dose, the more radiation defects are generated. The gate bias reduces the initial recombination rate of electron-hole pairs caused by irradiation, increases the number of holes escaping the initial recombination, and further increase the concentration of defect charge. The high-temperature environment causes tunneling annealing or thermal excitation annealing, which is conducive to the recovery of device performance.ConclusionsThe radiation damage process and mechanism of gallium nitride power devices of this study provides data support for evaluating and verifying its application in a space environment.

BackgroundAccurately calculating the borehole size and standoff between the tool and borehole wall is the premise for correcting the effect of the borehole environment and improving measurement precision in logging while drilling (LWD).PurposeThis study aims to obtain an accurate calculation method for the standoff size of LWD.MethodsFirstly, the theoretical relationship of the standoff was derived based on the broad-beam γ-ray attenuation model for azimuth density LWD. Then, Monte Carlo N-Particle transport code (MCNP) was employed for simulation, and results were benchmarked according to experimental tool data. By analyzing the influence of standoff, mud and formation density, and other factors on the detector response, an accurate standoff calculation formula was derived. Finally, logging curves were drawn using the CIFLog platform and the calculated standoff results were compared with the measured ultrasonic results, hence to verify the accuracy of the proposed standoff calculation method.ResultsThe calculated standoff results in the simulation are fundamentally consistent with the theoretical value. The calculation result using measured data processing is in approximate agreement with the ultrasonic standoff, and the calculated calipers have good correspondence with the wireline well diameter. The proposed method provides accurate measurement even when the standoff is small and ultrasonic standoff measurement is abnormal. The applicable range of standoff calculation based on azimuthal density LWD is 0~3.81 cm.ConclusionsThe broad-beam γ-ray attenuation based standoff calculation method for density LWD complements to larger range ultrasonic measurements to provide key parameters for borehole correction for LWD tools.

BackgroundAs a fundamental property of peptide molecules, chirality has been demonstrated to play an important role in controlling the structures and characteristics of peptide supramolecular systems. However, the mechanism through which chirality takes effect has not been clarified.PurposeThis study aims to examine the self- and co-assembled nanostructures and analyze the intermolecular interactions that drive the assembly by employing diphenylalanine (FF), along with the core recognition sequence of Amyloid-β protein (Aβ) and its enantiomer D-Phe-D-Phe (ff), in a model system.MethodsA series of structural and morphological analyses were conducted in the experiments. First, the scanning electron microscopy (SEM) and atomic force microscopy (AFM) images of the assembled nanostructures were obtained to observe the microscopic morphology and topological structure of the assembled FF and ff. Subsequently, circular dichroism (CD) and Fourier transform infrared spectroscopy (FTIR) were employed to characterize the secondary structures of peptides in the nanostructures. Finally, fluorescence emission spectrum and X-ray diffraction (XRD) analyses revealed the intermolecular interactions between peptide and solvent molecules.ResultsThe findings demonstrate that FF and ff self-assemble into similar fibrous nanostructures, and their chirality primarily affects the interactions between peptide molecules, as well as those between peptide and water molecules. Furthermore, the formation of new crystalline phases for the co-assembly of FF and ff was confirmed by XRD.ConclusionsOur results may facilitate the understanding of the formation mechanism of amyloid fibers and design of peptide supramolecular materials.

BackgroundGenerally, pulse truncation events caused by measurement systems often present challenges to pulse height analysis in the field of spectroscopy and radiometry, resulting in spectral distortion.PurposeThis study aims to propose a composite neural network model for accurately estimating the heights of truncated pulses.MethodsFirstly, a long and short-term memory (LSTM) network was embedded into the UNet structure to construct a composite neural network model (LSTM-UNet). Then, the model was trained for height estimation of truncated pulses output by silicon drift detectors using a simulated pulse dataset for which the pulse amplitude matrix superimposed with noise was taken as input signal while the output signal was a set of expanded pulse heights. Finally, the performance of the model using relative error indicators was evaluated by analyses of powder iron ore and powder rock samples.ResultsThe average relative error of the UNet-LSTM model for pulse height estimation analysis on simulated pulse sequences is approximately 2.31%, which is 1.91% lower than the average relative error of traditional trapezoidal shaping algorithms. Verification results of the UNet-LSTM model on measured pulse sequences with different degrees of truncation show that the average relative error obtained during the height estimation of two samples and eight sets of offline pulse sequences is 2.36%.ConclusionsThe results reveal that the proposed model can accurately estimate truncated pulse heights.

BackgroundNuclear power simulation technology has been widely applied in areas such as reactor design, safety analysis, independent safety evaluation, accident mitigation measures, design and optimization of control and protection system, verification of advanced main control room design, and operator training. This technology has effectively improved the safety and economy of nuclear power plants.PurposeThis study aims to develop a real-time modeling and simulation platform for a liquid-fueled molten salt reactor (LF-MSR) based on the open-source and open architecture of the experimental physics and industrial control system (EPICS).MethodsFirst, the real-time interaction function of the LF-MSR system code, RELAP5-TMSR, was improved, and the control and protection system and human-machine interaction interface were extended. Then, the ThorTypography simulation platform was preliminarily developed for LF-MSR by integrating the above three main functional modules. Finally, ThorTypography was validated using the pump start-up experiment, pump coast-down experiment, natural circulation experiment, and reactivity insertion experiment from the Molten Salt Reactor Experiment (MSRE) as the benchmark.ResultsThe test results of ThorTypography are consistent with the calculation results of RELAP5-TMSR and are in good agreement with the MSRE data. Moreover, the total simulation time is consistent with the total physical problem time.ConclusionsThorTypography is suitable for real-time modeling and simulation of LF-MSR systems and can provide effective support for LF-MSR design, operation, and safety analysis.

BackgroundThe annular fuel assembly of lead-bismuth cooled fast reactor has many safety advantages, but during its operation, due to the corrosive effect of lead-bismuth coolant, it is prone to blockage accidents, resulting in deterioration of heat transfer and jeopardizing the integrity of the first barrier. Therefore, it is urgent to research and analyze the blockage accident for the annular fuel assembly of the lead-bismuth-cooled fast reactor.MethodsA 5×5 single annular fuel assembly model was established, and numerical simulations for blockage of the inner and outer channel were carried out with different blockage areas, blockage thicknesses, and axial position of the blockage based on the computational fluid dynamics (CFD) software Fluent. The temperature distribution of the claddings, the flow field distribution near the blockage, the mass flow change of the channel, the radial temperature distribution, and the heat distribution of the fuel element at the blockage are compared with the result in no-blockage case.ResultsSimulation results indicate that the increase in the blockage area leads to a significant increase in the cladding temperature of the blockage area, an expansion of the scope of the recirculation area expands, the position of the highest temperature point of the fuel pellet shifts to the blockage side, and the heat flux density on the blockage side decreases. When the blockage fraction is large, the changes of parameters are similar to the above conclusions as the blockage thickness increases; when the blockage is located at the entrance, the local temperature rise of the cladding is smaller than that when the blockage is located at the center; with the increase of the blockage area and thickness and as the blockage position gets closer to the entrance of the active zone, the flow loss of the inner channel increases significantly, while the flow of the outer channel is almost unaffected.ConclusionsTherefore, the damage is more serious when the blockage accident occurs in the inner channel.

BackgroundThe kilowatt reactor using stirling technology (KRUSTY) is a heat-pipe-cooled reactor experimental system that uses a Stirling engine to convert thermal energy to electricity, it is the only one published experimental data for heat-pipe-cooled reactor systems. The KRUSTY experimental data under different working scenarios include the cold startup and load change processes, heat pipe failure, reactivity insertion, and heat sink loss.PurposeThis study aims to validate the self-developed system transient analysis code named TAPIRS-D for the heat-pipe-cooled reactor concept using KRUSTY experimental data.MethodsFirstly, an in-house system code for a heat-pipe-cooled reactor named TAPIRS-D was introduced, with the main theoretical module briefly explained, including the reactor power calculation module, heat transfer module for fuel assembly, and heat pipes. Then, the TAPIRS-D was applied for the first time to the simulation of the key processes of the KRUSTY prototypic reactor test under normal operation and accident conditions. Finally, comparison between the simulation data and experimental data was conducted for the validation of this analysis code.ResultsComparison results demonstrate that the maximum relative prediction error for the fuel temperature is less than 2%, and the reactor power average prediction error is less than 10%.ConclusionsThe prediction trend of the numerical simulation by TAPIRS-D fits well with the experimental data on key parameters such as core power and the temperature of fuel and heat pipes, which indicates that TAPIRS-D is well developed and is capable of conducting safety analysis for heat pipe cooled reactor concepts. The validation of this system analysis code provides a good reference for other newly developed system codes for heat pipe reactors.

BackgroundMolten salt reactors (MSRs) are fourth-generation advanced nuclear energy systems that exhibit characteristics such as high safety, high economy, nonproliferation, and sustainability. To ensure the safe operation of MSRs, identifying transient conditions promptly and accurately is crucial. However, current system transient identification methods rely on manual identification by operators, introducing significant human factors seriously affecting nuclear power safety.PurposeThis study aims to establish a transient identification model for an MSR system based on the K-nearest neighbor (KNN) method, so as to reduce human factors introduced during the traditional system transient identification process, and improve the operational safety of the MSR.MethodsDatasets for the system transient identification model were generated by using the RELAP5-TMSR code to simulate 11 operating conditions of the molten salt reactor experiment (MSRE) built and operated at Oak Ridge National Laboratory in the United States. Subsequently, a system transient identification model based on the KNN method was developed by training, optimizing, and validating these datasets. Four metrics, i.e., accuracy, precision, recall, and F1-score were applied to evaluating the system transient identification model. Finally, the robustness of the model was tested and optimized under noisy conditions.ResultsThe results demonstrate that the KNN-based transient identification model for the MSR system achieves a 99.99% F1-score on the test datasets. The system transient identification model also exhibits high robustness, with an F1-score of 94.32% under noisy conditions. The optimized system transient identification model achieves a 99.73% F1-score when identifying transient conditions under noise, accurately identifying the transient conditions of the MSRE.ConclusionsThe KNN-based transient identification model for the MSR system can satisfy the requirements of transient identification of the MSR system, hence be applied to intelligent MSR operations and maintenance, ensuring safe MSR operation.

BackgroundInstitute of Modern Physics, Chinese Academy of Sciences is developing a high-precision calibration device for lead-bismuth flowmeters based on the static mass method. In static mass method-based calibration devices, the uncertainty component of the diverter is the main component of the uncertainty of the flowmeter calibration device.PurposeThis study aims to predict the system error of a cylinder-driven diverter due to the asymmetry of cylinder forward and reverse strokes in the calibration process of lead-bismuth flowmeters, realize the a priori analysis of class B uncertainty components of a cylinder-driven commutator, and investigate whether the class B uncertainty can accurately reflect the magnitude of the relative system error introduced by the diverter.MethodsFirstly, a two-way coupling calculation method based on computational fluid dynamics (CFD) was developed for the diverter, and the SST k-ω turbulence model and Euler multiphase flow model were employed for calculation. Then, the stroke difference method was employed to obtain the class B uncertainty components for the diverter under different flow conditions and torque drives, and the calibration relative system errors under different timing methods and velocity distributions at the commutator nozzle outlet were calculated. Finally, the operating characteristics of the cylinder-driven diverter were analyzed.Results & ConclusionsComputation results show that the greater the thrust of the cylinder, the smaller is the type B uncertainty of the diverter. Compared to using the start or end of stroke as the timing moment, the calibration error caused by the diverter is the lowest when the diverter baffle is moved to the midpoint of the stroke as the timing moment, and the error is approximately 1/7?1/30 times those of the other two timing methods. The magnitude of diverter class B uncertainty reflects the envelope value of the relative systematic error caused by the diverter when using different timing moments.

BackgroundThe in-vessel retention (IVR) strategy is an important measure for mitigating severe reactor accidents. It has been successfully applied to the severe-accident management of advanced pressurized water reactors such as the AP1000, HPR1000, and CAP1400. In the implementation of the IVR strategy, the lower head is deformed by the heat load of the high-temperature melt. This affects the heat-removal capacity of the pressure-vessel external cooling and the successful implementation of the IVR strategy. It is necessary to examine the stress, failure, and deformation of the lower head.PurposeThis study aims to develop a large deformation model for the pressure-vessel lower head and analysis of its application in the FOREVER experiment.MethodsA mechanistic model called the lower-head large-deformation model was developed to address the limitations of the simplified film stress model of the Integrated Severe Accident Analysis (ISAA) program Lower Head Thermal Creep Module (LHTCM), which is very simple, and the absence of a deformation calculation module in the LHTCM model. This model was based on Timoshenko plate and shell theory, the Norton creep law, and large-deformation plasticity theory. Then, the model was integrated into the ISAA program to calculate the FOREVER-EC2 experiment.ResultsThe overall deformation result predicted by the large-deformation model exhibits the characteristic egg-like shape, with maximum displacement occurring at the bottom position of the lower head. The failure time predicted by the large-deformation model is 394.33 min, with an error of only 1.9% relative to the experiment. The predicted bottom elongation is consistent with the experimentally measured value. Additionally, the predicted location of the breach is consistent with the experiment, occurring between 75o and 85°.ConclusionsThe lower-head large-deformation model of this study can accurately predict the stress, failure time, overall deformation, and location of the breach of the lower head in a severe core melting accident.