BackgroundThe Shanghai soft X-ray Free Electron Laser (SXFEL) and the Shanghai High repetition rate XFEL and Extreme light facility (SHINE) are equipped with various high-power microwave components, including traveling wave accelerating tubes, deflection cavities, pulse compressors, etc.PurposeThis study aims to develop two high-power stainless steel absorbing loads, so as to meet the testing and operational requirements of these components at high power levels.MethodsFirstly, an initial load model was designed through simulation methods, and the microwave parameters were optimized. Then, the convection heat transfer coefficient in the waterway was calculated using theoretical calculations. Based on this information, thermal analysis was conducted on the mechanical model of the load to determine its temperature distribution under working conditions. Finally, the loads were manufactured and their RF parameters were measured using a vector network analyzer both in the clamping state and after welding.ResultsThe two X-band loads feature a waveguide structure with periodic grooves, and are operated at 11.424 GHz and 11.988 GHz respectively. The simulation results show that the bandwidth of two loads below -20 dB near the center frequency reaches over 100 MHz. The experimental test results are in good agreement with the simulation calculation results, meeting the design requirements.ConclusionsThe developed high power X-band dry loads described in this study satisfy operating requirements for SXFEL and SHINE.

BackgroundBoron neutron capture therapy (BNCT) is a highly promising and precise cancer treatment technique with substantial application prospects worldwide. The neutron transport process directly influences beam characteristics and accuracy of treatment planning.PurposeThis study aims to use the advanced Monte Carlo software, NECP-MCX, to investigate the neutron transport in an accelerator-driven BNCT (AB-BNCT) device.MethodsThe advanced Monte Carlo software, NECP-MCX, was used to investigate the neutron transport in an AB-BNCT device and calculate the beam parameters at the exit of the beam-shaping assembly (BSA), and results were compared with that calculated using the mainstream Monte Carlo software MCNP software. The relative biological dose deposition in Snyder head phantoms using various databases was calculated using both NECP-MCX and MCNP for comparative analysis. [Results andConclusions] The results show that in the design of the designated beam-shaping assembly, the neutron beam parameters obtained from NECP-MCX simulations minimally deviated from those calculated using the mainstream Monte Carlo software. The values satisfy the specifications of the International Atomic Energy Agency, confirming the applicability of NECP-MCX for neutron transport simulation in AB-BNCT. Regarding the Snyder head phantom, the relative biological dose parameters obtained by matching NECP-MCX with different databases satisfy clinical treatment standards, providing a foundation for selecting databases in the biological-based treatment planning system.

BackgroundEfficiency calibration is an important prerequisite for γ-spectroscopy measurement, and its accuracy directly affects the reliability of measurement results. The commonly used efficiency calibration methods are active efficiency calibration based on experimental measurement and passive efficiency calibration based on Monte Carlo (MC) simulations.PurposeThis study aims to propose a sourceless efficiency calibration method for γ spectrum based on numerical analysis.MethodsBased on theoretical analysis and numerical calculation, a passive efficiency calibration method based on numerical analysis was established, and applied to a constructed geometric model for typical cylindrical LaBr3(Ce) and NaI(Tl) detector with a diameter and length of 3.8 cm. The γ-ray path trajectory inside the detector, relative position of the source and detector, and peak-to-total ratio were comprehensively analyzed. Efficiency formulas for radioactive point, surface, and volume radioactive sources were formulated. Then, a numerical integration program based on Simpson's algorithm was implemented in MATLAB to solve the numerical analytical formula, and applied to the calculation of detection efficiencies of the 3.8 cm cylindrical LaBr3(Ce) and NaI(Tl) detectors for isotropic 137Cs point, surface, and volume sources. The calculation was performed again by changing the position of the point source and the size of the surface and volume sources. Simultaneously, the Monte Carlo (MC) simulation software MCNP5 was employed to establish the physical model of the detector, and the F8 pulse amplitude card was used to calculate the detection efficiency of the detector for specific energy γ-rays. Finally, detection efficiency obtained by numerical calculation was compared with that of MC simulation to verify the efficiency of proposed sourceless efficiency calibration method for γ spectrum.ResultsCompared with the MC simulation results, the maximum error of numerical calculation does not exceed 3.5%, and the maximum relative errors of the point source efficiency, surface source efficiency and volume source efficiency are 3.26%, 3.33% and 3.36%, repectively, which proves the reliability and accuracy of the numerical analysis method in calculating the detection efficiency.ConclusionsThe passive efficiency calibration method proposed in this study is accurate and fast, avoids complicated MC simulation software, which tends to be difficult to understand and operate. Additionally, this work can be extended to the efficiency calibration of nuclear radiation detectors with different shapes, providing a new pathway for the efficiency calibration of detectors.

BackgroundPhotonuclear reactions and compact neutron sources have emerged as promising tools for the production of medical isotopes, providing alternatives to conventional reactor-based high-enriched uranium methods. East China University of Technology (ECUT) is currently constructing an electron accelerator-driven photoneutron source (ECANS) for medical isotope production research.PurposeThis study aims to investigate the photonuclear reaction with 100Mo isotope and utilize the generated neutrons for isotopic production.MethodsFirstly, the photonuclear reactions of 100Mo was analyzed in details. The neutron spectrum and activation yield of 99Mo within a high purity 100Mo target were investigated. Then, a new model to produce medical isotopes was established on the basis of the ECANS photonuclear source, comprising neutron energy modulation layer and neutron reflection layer. Finally, the production yields of 99Mo, 177Lu, and 90Y in various natural oxides were calculated and the feasibility of using photonuclear sources for medical isotope production was assessed. The content of radioactive impurities in natural oxides under irradiation conditions was also analyzed.ResultsSimulation results demonstrate that photo-nuclear reactions can effectively produce medical isotopes such as 99Mo, 177Lu, and 90Y, with respective activities of 0.64 TBq·d-1, 0.67 TBq·d-1, and 2.11 TBq·d-1. And in the high purity 100Mo target, the daily output of 99Mo reaches 2.00 TBq·d-1.ConclusionsThis study demonstrates the feasibility of using the photodisintegration reaction of 100Mo as a neutron source for secondary production of medical isotopes, offering the potential to enhance the economic viability of isotope production. The approach of this study provides preliminary insights for subsequent separation and purification processes, hence has certain reference value for the development of tools for radioactive isotope production.

BackgroundWith the development of materials science and technology, more and more novel neutron shielding materials have been studied and prepared. The test of thermal neutron shielding performance of materials is an important measure of evaluating the shielding performance of novel neutron shielding materials, and provides important guidance for the improvement and application of materials. Special attention has been paid to the thermal neutron shielding properties of some thin materials, such as radiation protection fibers, shielding coatings, radiation protection rubber, composites with thermal neutron absorbers. At present, it is not easy to obtain pure thermal neutron field based on isotope neutron source, and the commonly used thermal neutron detector has a wide energy response range, and there is no unified test standard, hence the accuracy of the test results of thermal neutron shielding performance of materials needs to be further improved.PurposeThis study aims to propose an accurate method for testing the thermal neutron shielding properties of materials and to design a corresponding test platform.MethodsA thermal neutron shielding performance testing method based on the "cadmium filter method" was proposed and a corresponding testing platform was established. Firstly, the platform was based on a 252Cf isotope neutron source and a 3He proportional counter, with the design principle of minimizing errors. Then, Monte Carlo simulation method was used to optimize the materials and dimensions of the radiation shield, neutron moderator, collimator, and detector shield of the platform. The system error caused by the testing principle was reduced by further optimizing the cadmium filter method, and a collimating neutron beam launcher was designed to improve the collimation effect of the neutron beam, increase the thermal neutron fluence rate and thermal neutron share, and reduce the random error and the system error caused by the system design. Finally, the thermal neutron shielding performance of the materials commonly used in the nuclear field were tested and corresponding simulation calculations were carried out to verify the feasibility and accuracy of the test method. Five factors affecting shielding performance testing, i.e., detector type, neutron source intensity, distance to detector, detection system centerline offset, and neutron source type were analyzed simultaneously.ResultsThe actual test results are in good agreement with the simulation results, with excellent repeatability and reproducibility under different influencing factors.ConclusionsThis study provides an effective means to accurately evaluate the thermal neutron shielding properties of materials.

BackgroundThe exploration of mineral resources and geological structures is crucial for the sustainable development of the economy, society, and environment. Cosmic ray muons, a type of natural background radiation, can be utilized in muon transmission imaging which is based on density differences of transmitted target.PurposeThis study aims to enable non-contact, long-range, and non-destructive imaging of target objects, making it a powerful complement to traditional exploration methods for mineral resources.MethodsThe Geant4 software was utilized to simulate the physical processes of cosmic ray muons with materials of varying densities, and the shallow and deep geological structures were explored using a "telescope" configuration for muon transmission imaging. Firstly, the discriminability of muon imaging technology for substances with varying percentage density differences in rocks. For the simulation of, a volcanic model was constructed and four muon detectors was employed for simulating the imaging of the shallow geological structures from different angles, ensuring coverage of the entire mountain. Then, muon detectors located 600 m underground were utilized to extend exploration above unexplored areas with varying scales of undiscovered gold ore to obtain deep geological structures. Muons with energy lower than the minimum penetrating energy along their paths were absorbed by objects whilst muons that reached the detectors carried information about the materials along their paths. Meanwhile, the collected ray information was utilized to establish a density inversion model to obtain the minimum penetrating energy for each path, enabling the deduction of opacity distribution. Finally, the density distribution of volcanic model was determined by combining the geometric structure of the detected object, and individual detection points enabled two-dimensional monitoring whilst multiple detection points allowed for three-dimensional monitoring.ResultsThe imaging results of simulation show that the muon transmission imaging method can differentiate between different geological structures when the density difference exceeds 5%. In deep geological exploration, due to the low muon flux, imaging requires more time to accumulate sufficient muon events. Muon transmission imaging technology can effectively identify mineral deposits within deep rock formations when the difference in opacity between the path of muon penetration through the gold ore and the surrounding rock is greater than 4%.ConclusionsResults of his study demonstrate that the cosmic ray muon transmission imaging technology can be applied to geological exploration to achieve non-destructive exploration and obtain higher imaging accuracy when there is a reasonable density difference in the mineral resources and geological structures of the exploration area.

BackgroundThe defects generated during the working process of metal materials have a significant impact on their performance. For example, the radiation-induced embrittlement and hardening of reactor pressure vessel (RPV) steels are a factor of concern, which hinders the life extension of the RPV. Annealing treatment is applied to alleviating irradiation-induced precipitates and defects and recover RPV's mechanical properties in the past few decades to extend the in-service lifetime of the RPV. Unfortunately, this conventional method generally requires a high treatment temperature and long operation time, inevitably wasting considerable energy due to the huge size of the RPV. Recently, as a more convenient and energy-saving method, the repair of metal defects by electropulsing treatment (EPT) has been developed.PurposeThis study aims to design and construct a device for EPT processing of samples, and investigate the repairs of defects in electron irradiated and deformed iron and RPV steel after EPT by using positron lifetime spectroscopy.MethodsElectron irradiated pure iron and RPV steel samples were prepared and subjected to multi parameter EPT device developed in laboratory, and the changes in defects of the samples with EPT were characterized by positron lifetime spectroscopy. In addition, the mechanical properties of pure iron tensile samples were characterized by micro Vickers hardness, and the defect information was characterized by positron lifetime spectroscopy to explore the relationship between macroscopic properties and microstructure.ResultsThe defects introduced by electron irradiation in pure iron and RPV steel samples gradually recover after EPT and exhibit similar patterns to annealing treatment. After stretching, the number of defects in pure iron samples increases, leading to an increase in Vickers hardness. EPT can restore defect and reduce Vickers hardness.ConclusionsThe defects generated by irradiation or deformation in pure iron and RPV steel can be partially repaired through EPT. The effect of defect repair is not only related to the initial state of the sample, but also to EPT's parameters. As a new non-destructive testing method, positron annihilation is expected to provide a criterion for material damage or defect repair under the action of pulse current, which can conveniently, quickly, and sensitively detect the defect state of actual working components.

BackgroundThe use of controlled X-ray sources instead of 137Cs radioactive sources in density logging has become a new trend. The intensity of the X-ray source is substantially influenced by the high voltage on the target substrate, and the density measurement uncertainty can be maintained at 0.01 g·cm-3 when the high voltage is 350 kV.PurposeThis study aims to analyze the parameters of the shielding material and thickness suitable for the 350 kV high-voltage X-ray density logging instrument.MethodsThe Monte Carlo method was used to analyze the energy spectrum and counting rate of X-rays passing through different materials and thicknesses. By comparing the correlation between the 0~0.15 MeV and 0.15~0.35 MeV energy windows, the reasons for the difference between the X-ray attenuation and detector count rate in different energy windows were determined. In addition, combined with the actual instrument model construction of the four-detector X-ray density logging instrument, the influence of the three parts of particles on the detector was primarily considered. The placement mode and optimal thickness of each part of the shield for detectors were analyzed and designed using Monte Carlo N-particle (MCNP) simulation.ResultsThe simulation results show that the attenuation of X-rays in high- and low-energy windows increases with increase of atomic number and thickness of shielding materials. When tungsten nickel iron alloy is selected as the shielding material for the four-detector X-ray density logging instrument model, the suitable thickness of the shield between the base and the near-source detector is 1.75 cm. Meanwhile, to maintain the high voltage of X-ray generator at 350 kV, a shield layer with a thickness of 0.2 cm is placed between each detector, and a shield layer with a thickness of 0.35 cm is added to the back of the detector.ConclusionsThis study provides the design theory and key parameters for shielding materials and structures in the development of X-ray density logging tool.

BackgroundThe 1.2 MeV/10 mA electron accelerator, as one of electron irradiation sources for comprehensive irradiation test chamber in Space Environment Simulation and Research Infrastructure (SESRI), can provide electron beams on the millimeter scale. However, the electron beam, as the electron irradiation source in space environment ground simulation experiment for aerospace, must be uniformly irradiated on large objects. Therefore, a well-suited irradiated technique is significant.PurposeThis study aims to obtain beam scanning with less than 10% of inhomogeneity for 0.6 MeV, 1.0 MeV, 1.2 MeV electron beam for SESRI.MethodsBased on the overall irradiation requirements, a specific beam-scanning system, including the scanning magnet with customized design, digital power supply and a dedicated apparatus for beam uniformity measurement, was developed. Particularly, in order to eliminate the influence of 45° incidence of electron beam upon scanning uniformity, an asymmetric and non-standard triangular waveform for the magnetic field excitation current was employed and implemented. The measurements for the beam non-uniformity were carried out on field experiments.ResultsExperimental results show that the scanning area of this electron accelerator reaches 1 000 mm×1 000 mm, and the scanning nonuniformity is less than 10% for variable beam energy from 0.6 MeV to 1.2 MeV, achieving the design goal and satisfying the irradiation requirements of SESRI.ConclusionsA specific beam-scanning system developed for SESRI is verified in this study, offering a good reference for any similar beam-scanning scenarios.