Vol.35,

Time-encoded imaging is useful for identifying potential special nuclear materials and other radioactive sources at a distance. In this study, a large field-of-view time-encoded imager was developed for gamma-ray and neutron source hotspot imaging based on a depth-of-interaction (DOI) detector. The imager primarily consists of a DOI detector system and a rotary dual-layer cylindrical coded mask. An EJ276 plastic scintillator coupled with two SiPMs was designed as the DOI detector to increase the field of view and improve the imager performance. The difference in signal time at both ends and the log of the signal amplitude ratio were used to calculate the interaction position resolution. The position resolution of the DOI detector was calibrated using a collimated Cs-137 source, and the full width at half maximum of the reconstruction position of the Gaussian fitting curve was approximately 4.4 cm. The DOI detector can be arbitrarily divided into several units to independently reconstruct the source distribution images. The unit length was optimized via Am-Be source-location experiments. A multidetector filtering method is proposed for image denoising. This method can effectively reduce image noise caused by poor DOI detector position resolution. The vertical field of view of the imager was (-55°, 55°) when the detector was placed in the center of the coded mask. A DT neutron source at 20 m standoff could be located within 2400 s with an angular resolution of 3.5°.

569

The High Energy Fragment Separator (HFRS), which is currently under construction, is a leading international radioactive beam device. Multiple sets of position-sensitive Twin Time Projection Chamber (TPC) detectors are distributed on HFRS for particle identification and beam monitoring. The twin TPCs’ readout electronics system operates in a trigger-less mode due to its high counting rate, leading to a challenge of handling large amounts of data. To address this problem, we introduced an event-building algorithm. This algorithm employs a hierarchical processing strategy to compress data during transmission and aggregation. In addition, it reconstructs twin TPCs’ events online and stores only the reconstructed particle information, which significantly reduces the burden on data transmission and storage resources. Simulation studies demonstrated that the algorithm accurately matches twin TPCs’ events and reduces more than 98% of the data volume at a counting rate of 500 kHz/channel.

517

The Coherent Muon-to-Electron Transition (COMET) experiment is a leading experiment for the coherent conversion of μ^-N→e^-N using a high-intensity pulsed muon beamline, produced using innovative slow-extraction techniques. Therefore, it is critical to measure the muon beam characteristics. We set up a muon beam monitor (MBM), where scintillating fibers woven in a cross shape were coupled to silicon photomultipliers to measure the spatial profile and timing structure of the extracted muon beam for the COMET. The MBM detector was tested successfully with a proton beamline at the China Spallation Neutron Source and took data with good performance in the commissioning run. The development of the MBM, including its mechanical structure, electronic readout, and beam measurement results, are discussed.

527

This paper presents a new technique for measuring the bunch length of a high-energy electron beam at a bunch-by-bunch rate in storage rings. This technique uses the time–frequency-domain joint analysis of the bunch signal to obtain bunch-by-bunch and turn-by-turn longitudinal parameters, such as bunch length and synchronous phase. The bunch signal is obtained using a button electrode with a bandwidth of several gigahertz. The data acquisition device was a high-speed digital oscilloscope with a sampling rate of more than 10 GS/s, and the single-shot sampling data buffer covered thousands of turns. The bunch length and synchronous phase information were extracted via offline calculations using Python scripts. The calibration coefficient of the system was determined using a commercial streak camera. Moreover, this technique was tested on two different storage rings and successfully captured various longitudinal transient processes during the harmonic cavity debugging process at the Shanghai Synchrotron Radiation Facility (SSRF), and longitudinal instabilities were observed during the single bunch accumulation process at Hefei Light Source (HLS). For Gaussian-distribution bunches, the uncertainty of the bunch phase obtained using this technique was better than 0.2 ps, and the bunch length uncertainty was better than 1 ps. The dynamic range exceeded 10 ms. This technology is a powerful and versatile beam diagnostic tool that can be conveniently deployed in high-energy electron storage rings.

492

Neutron radiography is a crucial nondestructive testing technology widely used in the aerospace, military, and nuclear industries. However, because of the physical limitations of neutron sources and collimators, the resulting neutron radiographic images inevitably exhibit multiple distortions, including noise, geometric unsharpness, and white spots. Furthermore, these distortions are particularly significant in compact neutron radiography systems with low neutron fluxes. Therefore, in this study, we devised a multi-distortion suppression network that employs a modified generative adversarial network to improve the quality of degraded neutron radiographic images. Real neutron radiographic image datasets with various types and levels of distortion were built for the first time as multi-distortion suppression datasets. Thereafter, the coordinate attention mechanism was incorporated into the backbone network to augment the capability of the proposed network to learn the abstract relationship between ideally clear and degraded images. Extensive experiments were performed; the results show that the proposed method can effectively suppress multiple distortions in real neutron radiographic images and achieve state-of-the-art perceptual visual quality, thus demonstrating its application potential in neutron radiography.

657

The High Energy Cosmic-Radiation Detection (HERD) facility is planned to launch in 2027 and scheduled to be installed on the China Space Station. It serves as a dark matter particle detector, a cosmic ray instrument, and an observatory for high-energy gamma rays. A transition radiation detector placed on one of its lateral sides serves dual purpose, (i) calibrating HERD’s electromagnetic calorimeter in the TeV energy range, and (ii) serving as an independent detector for high-energy gamma rays. In this paper, the prototype readout electronics design of the transition radiation detector is demonstrated, which aims to accurately measure the charge of the anodes using the SAMPA application specific integrated circuit chip. The electronic performance of the prototype system is evaluated in terms of noise, linearity, and resolution. Through the presented design, each electronic channel can achieve a dynamic range of 0-100 fC, the RMS noise level not exceeding 0.15 fC, and the integral nonlinearity was less than 0.2%. To further verify the readout electronic performance, a joint test with the detector was carried out, and the results show that the prototype system can satisfy the requirements of the detector’s scientific goals.

636

In the research and development of new silicon pixel detectors, a collimated monoenergetic charged-particle test beam equipped with a high-resolution pixel-beam telescope is crucial for prototype verification and performance evaluation. When the beam energy is low, the effect of multiple Coulomb scattering on the measured resolution of the Device Under Test (DUT) must be considered to accurately evaluate the performance of the pixel chips and detectors. This study aimed to investigate the effect of multiple Coulomb scattering on the measured resolution, particularly at low beam energies. Simulations were conducted using Allpix² to study the effects of multiple Coulomb scattering under different beam energies, material budgets, and telescope layouts. The simulations also provided the minimum energy at which the effect of multiple Coulomb scattering could be ignored. Compared with the results of a five-layer detector system tested with an electron beam at DESY, the simulation results were consistent with the beam test results, confirming the reliability of the simulations.

405

A molten salt reactor (MSR) has outstanding features considering the application of thorium fuel, inherent safety, sustainability, and resistance to proliferation. However, fissile material ²³³U is significantly rare at the current stage, thus it is difficult for MSR to achieve a pure thorium-uranium fuel cycle. Therefore, using plutonium or enriched uranium as the initial fuel for MSR is more practical. In this study, we aim to verify the feasibility of a small modular MSR that utilizes plutonium as the starting fuel (SM-MSR-Pu), and highlight its advantages and disadvantages. First, the structural design and fuel management scheme of the SM-MSR-Pu were presented. Second, the neutronic characteristics, such as the graphite-irradiation lifetime, burn-up performance, and coefficient of temperature reactivity were calculated to analyze the physical characteristics of the SM-MSR-Pu. The results indicate that plutonium is a feasible and advantageous starting fuel for a SM-MSR; however, there are certain shortcomings that need to be solved. In a 250 MWth SM-MSR-Pu, approximately 288.64 kg ²³³U of plutonium with a purity of greater than 90% is produced while 978.00 kg is burned every ten years. The temperature reactivity coefficient decreases from -4.0 pcm K^-1 to -6.5 pcm K^-1 over the 50-year operating time, which ensures a long-term safe operation. However, the amount of plutonium and accumulation of minor actinides (MAs) would increase as the burn-up time increases, and the annual production and purity of ²³³U will decrease. To achieve an optimal burn-up performance, setting the entire operation time to 30 years is advisable. Regardless, more than 3600 kg of plutonium eventually accumulate in the core. Further research is required to effectively utilize this accumulated plutonium.

590

The heterogeneous variational nodal method (HVNM) has emerged as a potential approach for solving high-fidelity neutron transport problems. However, achieving accurate results with HVNM in large-scale problems using high-fidelity models has been challenging due to the prohibitive computational costs. This paper presents an efficient parallel algorithm tailored for HVNM based on the Message Passing Interface standard. The algorithm evenly distributes the response matrix sets among processors during the matrix formation process, thus enabling independent construction without communication. Once the formation tasks are completed, a collective operation merges and shares the matrix sets among the processors. For the solution process, the problem domain is decomposed into subdomains assigned to specific processors, and the red-black Gauss-Seidel iteration is employed within each subdomain to solve the response matrix equation. Point-to-point communication is conducted between adjacent subdomains to exchange data along the boundaries. The accuracy and efficiency of the parallel algorithm are verified using the KAIST and JRR-3 test cases. Numerical results obtained with multiple processors agree well with those obtained from Monte Carlo calculations. The parallelization of HVNM results in eigenvalue errors of 31 pcm/-90 pcm and fission rate RMS errors of 1.22%/0.66%, respectively, for the 3D KAIST problem and the 3D JRR-3 problem. In addition, the parallel algorithm significantly reduces computation time, with an efficiency of 68.51% using 36 processors in the KAIST problem and 77.14% using 144 processors in the JRR-3 problem.

525

A dedicated weak current measurement system was designed to measure the weak currents generated by the neutron ionization chamber. This system incorporates a second-order low-pass filter circuit and the Kalman filtering algorithm to effectively filter out noise and minimize interference in the measurement results. Testing conducted under normal temperature conditions has demonstrated the system’s high precision performance. However, it was observed that temperature variations can affect the measurement performance. Data was collected across temperatures ranging from -20 to 70 ℃, and a temperature correction model was established through linear regression fitting to address this issue. The feasibility of the temperature correction model was confirmed at temperatures of -5 and 40 ℃, where relative errors remained below 0.1% after applying the temperature correction. The research indicates that the designed measurement system exhibits excellent temperature adaptability and high precision, making it particularly suitable for measuring weak currents.

667

Dispersion fuels, knowned for their excellent safety performance, are widely used in advanced reactors, such as high-temperature gas-cooled reactors (HTGRs). Compared with deterministic methods, the Monte Carlo method has more advantages in the geometric modeling of stochastic media. The explicit modeling method has high computational accuracy and high computational cost. The chord length sampling (CLS) method can improve computational efficiency by sampling the chord length during neutron transport using the matrix chord length's probability density function (PDF). This study shows that the excluded-volume effect in realistic stochastic media can introduce certain deviations into the CLS. A chord length correction approach is proposed to obtain the chord length correction factor by developing the Particle code based on equivalent transmission probability. Through numerical analysis against reference solutions from explicit modeling in the RMC code, it was demonstrated that CLS with the proposed correction method provides good accuracy for addressing the excluded-volume effect in realistic infinite stochastic media.

430

Because of their economy and applicability, high-power thyristor devices are widely used in the power supply systems for large fusion devices. When high-dose neutrons produced by deuterium-tritium (D-T) fusion reactions are irradiated on a thyristor device for a long time, the electrical characteristics of the device change, which may eventually cause irreversible damage. In this study, with the thyristor switch of the commutation circuit in the quench protection system (QPS) of a fusion device as the study object, the relationship between the internal physical structure and external electrical parameters of the irradiated thyristor is established. Subsequently, a series of targeted thyristor physical simulations and neutron irradiation experiments are conducted to verify the accuracy of the theoretical analysis. In addition, the effect of irradiated thyristor electrical characteristic changes on the entire QPS is studied by accurate simulation, providing valuable guidelines for the maintenance and renovation of the QPS.

574

Prompt radiation emitted during accelerator operation poses a significant health risk, necessitating a thorough search and securing of hazardous areas prior to initiation. Currently, manual sweep methods are employed. However, the limitations of manual sweeps have become increasingly evident with the implementation of large-scale accelerators. By leveraging advancements in machine vision technology, the automatic identification of stranded personnel in controlled areas through camera imagery presents a viable solution for efficient search and security. Given the criticality of personal safety for stranded individuals, search and security processes must be sufficiently reliable. To ensure comprehensive coverage, 180° camera groups were strategically positioned on both sides of the accelerator tunnel to eliminate blind spots within the monitoring range. The YOLOV8 network model was modified to enable the detection of small targets, such as hands and feet, as well as larger targets formed by individuals near the cameras. Furthermore, the system incorporates a pedestrian recognition model that detects human body parts, and an information fusion strategy is used to integrate the detected head, hands, and feet with the identified pedestrians as a cohesive unit. This strategy enhanced the capability of the model to identify pedestrians obstructed by equipment, resulting in a notable improvement in the recall rate. Specifically, recall rates of 0.915 and 0.82 were obtained for Datasets 1 and 2, respectively. Although there was a slight decrease in accuracy, it aligned with the intended purpose of the search-and-secure software design. Experimental tests conducted within an accelerator tunnel demonstrated the effectiveness of this approach in achieving reliable recognition outcomes.

487

Beams typically do not travel through the magnet centers because of errors in storage rings. The beam deviating from the quadrupole centers is affected by additional dipole fields due to magnetic field feed-down. Beam-based alignment (BBA) is often performed to determine a golden orbit where the beam circulates around the quadrupole center axes. For storage rings with many quadrupoles, the conventional BBA procedure is time-consuming, particularly in the commissioning phase, because of the necessary iterative process. In addition, the conventional BBA method can be affected by strong coupling and the nonlinearity of the storage ring optics. In this study, a novel method based on a neural network was proposed to determine the golden orbit in a much shorter time with reasonable accuracy. This golden orbit can be used directly for operation or adopted as a starting point for conventional BBA. The method was demonstrated in the HLS-II storage ring for the first time through simulations and online experiments. The results of the experiments showed that the golden orbit obtained using this new method was consistent with that obtained using the conventional BBA. The development of this new method and the corresponding experiments are reported in this paper.

658

Currently, three types of superconducting magnets are used in particle accelerators: cos 2θ, CCT, and serpentine. However, all three coil configurations have complex spatial geometries, which make magnet manufacturing and strain-sensitive superconductor applications difficult. Compared with the three existing quadrupole coils, the racetrack quadrupole coil has a simple shape and manufacturing process, but there have been few theoretical studies. In this paper, the two-dimensional and three-dimensional analytical expressions for the magnetic field in coil-dominated racetrack superconducting quadrupole magnets are presented. The analytical expressions of the field harmonics and gradient are fully resolved and depend only on the geometric parameters of the coil and current density. Then, a genetic algorithm is applied to obtain a solution for the coil geometry parameters with field harmonics on the order of 10^-4. Finally, considering the practical engineering needs of the accelerator interaction region, electromagnetic design examples of racetrack quadrupole magnets with high gradients, large apertures, and small apertures are described, and the application prospects of racetrack quadrupole coils are analyzed.

510

Yang Zhang，Sheng-Quan Yan，Ming He，Qing-Zhang Zhao，Wen-Hui Zhang，Chao-Xin Kan，Jian-Ming Zhou，Kang-Ning Li，Xiao-Fei Wang，Jian-Cheng Liu，Zhao-Hua Peng，Zhuo Liang，Ai-Ling Li，Jian Zheng，Qi-Wen Fan，Yun-Ju Li，You-Bao Wang，Zhi-Hong Li，Yang-Ping Shen，Ding Nan，Wei Nan，Yu-Qiang Zhang，Jia-Ying-Hao Li，Jun-Wen Tian，Jiang-Lin Hou，Chang-Xin Guo，Zhi-Cheng Zhang，Ming-Hao Zhu，Yu-Wen Chen，Yu-Chen Jiang，Tao Tian，Jin-Long Ma，Yi-Hui Liu，Jing-Yu Dong，Run-Long Liu，Mei-Yue-Nan Ma，Yong-Shou Chen，Wei-Ping Liu，Bing Guo

The Moon provides a unique environment for investigating nearby astrophysical events such as supernovae. Lunar samples retain valuable information from these events, via detectable long-lived "fingerprint" radionuclides such as ⁶⁰Fe. In this work, we stepped up the development of an accelerator mass spectrometry (AMS) method for detecting ⁶⁰Fe using the HI-13 tandem accelerator at the China Institute of Atomic Energy (CIAE). Since interferences could not be sufficiently removed solely with the existing magnetic systems of the tandem accelerator and the following Q3D magnetic spectrograph, a Wien filter with a maximum voltage of ±60 kV and a maximum magnetic field of 0.3 T was installed after the accelerator magnetic systems to lower the detection background for the low abundance nuclide ⁶⁰Fe. A 1 μm thick Si₃N₄ foil was installed in front of the Q3D as an energy degrader. For particle detection, a multi-anode gas ionization chamber was mounted at the center of the focal plane of the spectrograph. Finally, an ⁶⁰Fe sample with an abundance of 1.125×10^-10 was used to test the new AMS system. These results indicate that ⁶⁰Fe can be clearly distinguished from the isobar ⁶⁰Ni. The sensitivity was assessed to be better than 4.3×10^-14 based on blank sample measurements lasting 5.8 h, and the sensitivity could in principle be expected to be approximately 2.5×10^-15 when the data were accumulated for 100 h, which is feasible for future lunar sample measurements because the main contaminants were sufficiently separated.

473

The High Altitude Detection of Astronomical Radiation (HADAR) experiment, which was constructed in Tibet, China, combines the wide-angle advantages of traditional EAS array detectors with the high-sensitivity advantages of focused Cherenkov detectors. Its objective is to observe transient sources such as gamma-ray bursts and the counterparts of gravitational waves. This study aims to utilize the latest AI technology to enhance the sensitivity of HADAR experiments. Training datasets and models with distinctive creativity were constructed by incorporating the relevant physical theories for various applications. These models can determine the type, energy, and direction of the incident particles after careful design. We obtained a background identification accuracy of 98.6%, a relative energy reconstruction error of 10.0%, and an angular resolution of 0.22-degrees in a test dataset at 10 TeV. These findings demonstrate the significant potential for enhancing the precision and dependability of detector data analysis in astrophysical research. By using deep learning techniques, the HADAR experiment’s observational sensitivity to the Crab Nebula has surpassed that of MAGIC and H.E.S.S. at energies below 0.5 TeV and remains competitive with conventional narrow-field Cherenkov telescopes at higher energies. In addition, our experiment offers a new approach for dealing with strongly connected, scattered data.

461

In this study, to efficiently remove Pb(II) from aqueous environments, a novel L-serine-modified polyethylene/polypropylene nonwoven fabric sorbent (NWF-serine) was fabricated through the radiation grafting of glycidyl methacrylate and subsequent L-serine modification. The effect of the absorbed dose was investigated in the range of 5–50 kGy. NWF-serine was characterized by Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. Batch adsorption tests were conducted to investigate the influences of pH, adsorption time, temperature, initial concentration, and sorbent dosage on the Pb(II) adsorption performance of NWF-serine. The results indicated that Pb(II) adsorption onto NWF-serine was an endothermic process, following the pseudo-second-order kinetic model and Langmuir isotherm model. The saturated adsorption capacity was 198.1 mg/g. NWF-serine exhibited Pb(II) removal rates of 99.8% for aqueous solutions with initial concentrations of 100 mg/L and 82.1% for landfill leachate containing competitive metal ions such as Cd, Cu, Ni, Mn, and Zn. Furthermore, NWF-serine maintained 86% of its Pb(II) uptake after five use cycles. The coordination of the carboxyl and amino groups with Pb(II) was confirmed using X-ray photoelectron spectroscopy and extended X-ray absorption fine structure analysis.

518