Vol.36,

The measurement of low-level radioactivity using high purity germanium (HPGe) detectors is important in applications such as environmental background radiation, material screening, and rare decays. The dead layers, dead zones, aluminum shell thickness, and diameter of Ge-crystals are the most influential factors affecting the performance of HPGe detectors; hence, precise modeling of the physical conditions of the detectors is highly desirable. In this study, the GEANT4 simulation framework with an optimized detector geometry adequately replicated the experimentally recorded spectrum. These detector simulations explored the idea of realizing a dead zone (an inactive volume) at the backend of an n-type coaxial Ge-crystal. Using multigamma sources, the effect of true coincidence summing (TCS) on the full energy peak (FEP) efficiency calibration of an HPGe detector was investigated as a function of sample-to-detector distance. Good agreements between the simulated and experimental efficiencies as well as the simulated and analytically calculated summing coincidence correction coefficients were achieved. At a short distance between the source and detector, calculating the correction factors for a strong source posed challenges owing to significant deadtime and pile-up effects of the detection system. The described methodology can efficiently determine summing peak probabilities at short sample-to-detector distances.

102

In this study, we comprehensively characterized and optimized a cryogenic pure CsI (pCsI) detector. We utilized a 2 cm×2 cm×2 cm cube crystal coupled with a HAMAMATSU R11065 photomultiplier tube, achieving a remarkable light yield of 35.2PE/keV_ee and an unprecedented energy resolution of 6.9% at 59.54 keV. Additionally, we measured the scintillation decay time of pCsI, which was significantly shorter than that of CsI(Na) at room temperature. Furthermore, we investigated the impact of temperature, surface treatment, and crystal shape on light yield. Notably, the light yield peaked at approximately 20 K and remained stable within the range of 70–100 K. The light yield of the polished crystals was approximately 1.5 times greater than that of the ground crystals, whereas the crystal shape exhibited minimal influence on the light yield. These results are crucial for the design of the 10 kg pCsI detector for the future CLOVERS (Coherent eLastic neutrinO(V)-nucleus scattERing at China Spallation Neutron Source (CSNS)) experiment.

116

A 20-kiloton liquid scintillator detector is under construction at the Jiangmen Underground Neutrino Observatory (JUNO) for several physics purposes. Detecting neutrinos released from nuclear reactors, the sun, supernova bursts, and Earth's atmosphere across a wide energy range necessitates efficient reconstruction algorithms. In this study, we introduce a novel method for reconstructing event energy by counting 3-inch photomultiplier tubes (PMTs) with or without signals. The proposed algorithm demonstrated excellent performance in accurate energy reconstruction, validated with electron Monte Carlo samples covering kinetic energies ranging from 10 MeV to 1 GeV.

100

The prompt fission neutron spectrum (PFNS) is a key nuclear data quantity that is of particular interest and plays a crucial role in understanding and modeling fission processes. An array comprising 48 liquid scintillation detectors and a parallel-plate avalanche counter (PPAC) was developed at the China Institute of Atomic Energy (CIAE) to measure the PFNS of actinide nuclei. Efficiency and energy calibrations were performed for all the liquid scintillators, and their efficiencies were consistently found to be better than 5%. The time resolutions of the PPAC and liquid scintillators were measured to be 1.08 ns and 1.16 ns using ²⁵²Cf and ²⁰⁷Bi sources, respectively. The pulse shape discrimination of the liquid scintillator was utilized to identify neutron and γ signals on an event-by-event basis, and the figure of merit was deduced as 1.12 at a 200 keVee threshold. The contribution to the PFNS from multiple scattered neutrons was evaluated via Geant4 simulations, and those originating from the environment were found to be comparable to the crosstalk between the detectors. The neutron efficiency of the entire detection array was calibrated using a ²⁵²Cf spontaneous fission source and was demonstrated to be consistent with the Geant4 simulation results, which verified the reliability of the detection array.

The Cooling Storage Ring (CSR) external-target experiment (CEE) will be the first large-scale nuclear physics experiment at the Heavy Ion Research Facility in Lanzhou (HIRFL). A beam monitor has been developed to monitor the beam status and to improve the reconstruction resolution of the primary vertex. Custom-designed pixel charge sensors, named Topmetal-CEEv1, are employed in the detector to locate the position of each particle. Readout electronics for the beam monitor were designed, including front-end electronics utilizing the Topmetal-CEEv1 sensors, as well as a readout and control unit that communicates with the DAQ, trigger, and clock systems. A series of tests were performed to validate the functionality and performance of the system, including basic electronic verifications and responses to α particles and heavy-ion beams. The results show that all designed functions of the readout electronics system work well, and this system could be used for beam monitoring in the CEE experiment.

105

The semi-cylindrical Time Projection Chamber (scTPC) is designed to measure the angular distribution of the cross-section for intermediate-energy (³He,t) charge-exchange reactions in inverse kinematics. The scTPC prototype comprises a cathode, field cage, drift region, amplification structure based on a multilayer thick gas electron multiplier (THGEM), and a readout plane with 886 zigzag-shaped pads. The gain uniformity of the THGEM and the drift velocity of electrons were calibrated. Track recognition based on the Hough transform was then developed to reconstruct cosmic ray tracks and determine their position resolution. The position resolution of secondary particle tracks resulting from collisions between the heavy-ion beam and the ³He target was measured, yielding an x-resolution of 0.71 mm and a z-resolution of 0.73 mm. The scTPC demonstrates sufficient energy and spatial resolution to support charge-exchange reaction experiments in inverse kinematics.

The Taishan Antineutrino Observatory (TAO) experiment features a top veto tracker system comprising 160 modules, each constructed from plastic scintillator (PS) strips, embedded wavelength shifting fibers (WLS-fibers), and silicon photomultipliers. This article reports on the performance of all produced modules, focusing on the production and readout/trigger design, and providing insights into scintillation detectors based on WLS-fibers. Three types of trigger modes and their efficiencies were defined to comprehensively evaluate the performance of this unique design, which was verified through batch production, comprehensive measurement strategies, and quality inspection methods. In "module" mode, the detection(tagging) efficiency of the PS exceeded 99.67% at a 30-photoelectron threshold, and even in "AND" mode, it surpassed 99.60% at a 15-photoelectron threshold. The muon tagging efficiency satisfies the requirements of TAO. The production and performance of PS modules establish a benchmark for other experiments, with optimized optical fiber arrangements that enhance light yield and muon detection efficiency.

671

Vulnerability assessment is a systematic process to identify security gaps in the design and evaluation of physical protection systems. Adversarial path planning is a widely used method for identifying potential vulnerabilities and threats to the security and resilience of critical infrastructures. However, achieving efficient path optimization in complex large-scale three-dimensional (3D) scenes remain a significant challenge for vulnerability assessment. This paper introduces a novel A^*-algorithmic framework for 3D security modeling and vulnerability assessment. Within this framework, the 3D facility models were first developed in 3ds Max and then incorporated into Unity for heuristic pathfinding A^*. The A^*-heuristic pathfinding algorithm was implemented with a geometric probability model to refine the detection and distance fields and achieve a rational approximation of the cost to reach the goal. An admissible heuristic is ensured by incorporating the minimum probability of detection (PDmin) and diagonal distance to estimate the heuristic function. The 3D A^* heuristic search was demonstrated using a hypothetical laboratory facility, where a comparison was also carried out between the A^* and Dijkstra algorithms for optimal path identification. Comparative results indicate that the proposed A^*-heuristic algorithm effectively identifies the most vulnerable adversarial pathfinding with high efficiency. Finally, the paper discusses hidden phenomena and open issues in efficient 3D pathfinding for security applications.

104

The thermal conductivity of plasma-facing materials (PFM) exposed to intense radiation is a critical concern for the reliable usage of materials in fusion reactors. However, limited research has been performed regarding the thermal conductivity of structures that rapidly change in a short time during collision cascade processes under irradiation. In this study, we employed the tight-binding (TB) method to investigate the electronic thermal conductivity (κ_e) of tungsten-based systems during various cascading processes. We found that κ_e values sharply decrease within the initial 0.3 picoseconds and then partially recover at a slow pace; this is closely linked to the evolution of defects and microstructural distortions. The increase in the initial kinetic energy of the primary knock-on atom and the presence of a high concentration of hydrogen atoms further decrease the κ_e values. Conversely, higher temperatures have a significant positive effect on κ_e. Furthermore, the presence of a grain boundary ∑5 [001](130) substantially reduces κ_e, whereas the absorption effect of point defects by the grain boundary has little influence on κ_e during cascades. Our findings provide a theoretical basis for evaluating changes in the thermal conductivity performance of PFMs during their usage in nuclear fusion reactors.

114

Artificial intelligence has potential for forecasting reactor conditions in the nuclear industry. Owing to economic and security concerns, a common method is to train data generated by simulators. However, achieving a satisfactory performance in practical applications is difficult because simulators imperfectly emulate reality. To bridge this gap, we propose a novel framework called simulation-to-reality domain adaptation (SRDA) for forecasting the operating parameters of nuclear reactors. The SRDA model employs a transformer-based feature extractor to capture dynamic characteristics and temporal dependencies. A parameter predictor with an improved logarithmic loss function is specifically designed to adapt to varying reactor powers. To fuse prior reactor knowledge from simulations with reality, the domain discriminator utilizes an adversarial strategy to ensure the learning of deep domain-invariant features, and the multiple kernel maximum mean discrepancy minimizes their discrepancies. Experiments on neutron fluxes and temperatures from a pressurized water reactor illustrate that the SRDA model surpasses various advanced methods in terms of predictive performance. This study is the first to use domain adaptation for real-world reactor prediction and presents a feasible solution for enhancing the transferability and generalizability of simulated data.

GPU-based Monte Carlo (MC) simulations are highly valued for their potential to improve both the computational efficiency and accuracy of radiotherapy. However, in proton therapy, these methods often simplify human tissues as water for nuclear reactions, disregarding their true elemental composition and thereby potentially compromising calculation accuracy. Consequently, this study developed the program gMCAP (GPU-based proton MC Algorithm for Proton therapy), incorporating precise discrete interactions, and established a refined nuclear reaction model (REFINED) that considers the actual materials of the human body. Compared to the approximate water model (APPROX), the REFINED model demonstrated an improvement in calculation accuracy of 3%. In particular, in high-density tissue regions, the maximum dose deviation between the REFINED and APPROX models was up to 15%. In summary, the gMCAP program can efficiently simulate 1 million protons within 1 second while significantly enhancing dose calculation accuracy in high-density tissues, thus providing a more precise and efficient engine for proton radiotherapy dose calculations in clinical practice.

114

The application of a controllable neutron source for measuring formation porosity in the advancement of nuclear logging has garnered increased attention. The existing porosity algorithm, which is based on the thermal neutron counting ratio, exhibits lower sensitivity in high- porosity regions. To enhance the sensitivity, the effects of elastic and inelastic scattering, which influence the slowing-down of fast neutrons, were theoretically analyzed and a slowing-down model of fast neutrons was created. Based on this model, a density correction porosity algorithm was proposed based on the relationship between density, thermal neutron counting ratio, and porosity. Finally, the super multi-functional calculation program for nuclear design and safety evaluation (TopMC/SuperMC), was used to create a simulation model for porosity logging, and its applicability was examined. The results demonstrated that the relative error between the calculated and actual porosities was less than 1%, and the influence of deviation in the density measurement was less than 2%. Therefore, the proposed density correction algorithm based on the slowing-down model of fast neutrons can effectively improve the sensitivity in the high-porosity region. This study is expected to serve as a reference for the application of neutron porosity measurements with D-T neutron sources.

Energy-variable gamma-rays are produced in Laser Compton Slant-scattering (LCSS) mode at the Shanghai Laser Electron Gamma Source (SLEGS), a beamline of the Shanghai Synchrotron Radiation Facility (SSRF, also called Shanghai Light Source). Based on the SLEGS energy-variable gamma-ray beam, a positron-generation system composed of a gamma-ray-driven section, positron-generated target, magnet separation section, and positron experimental section was designed for SLEGS. Geant4 simulation results show that the energy tunable positron beam in the energy range of 1 to 12.9 MeV with a flux of 3.7×10⁴ to 6.9×10⁵ e⁺/s can be produced in this positron-generation system. The positron beam generation and separation provide favorable experimental conditions for conducting non-destructive positron testing on SLEGS in the future. The positron-generation system is currently under construction and will be completed in 2025.

The Shanghai Laser Electron Gamma Source (SLEGS) delivers quasi-monochromatic, continuously energy-tunable γ-ray beams. Based on a Photon Activation Analysis (PAA) method, SLEGS built and developed a photon activation analysis platform, including online activation and offline low-background High-Purity Germanium (HPGe) detector measurement systems, as an alternative to direct measurement methods and low-throughput cross-tests. Owing to short half-lives spanning from minutes to days and characteristics such as ease of fabrication, cost-effectiveness, and stability, gold (¹⁹⁷Au) and zinc (⁶⁴Zn) emerge as favorable activation targets for the γ-ray beam flux monitor. Notably, they exhibit a multitude of advantages in monitoring the γ-ray beam flux, typically 10⁵ photons/s, with energies of 13.16 MeV to 19.08 MeV using a 3 mm coarse collimator. In particular, high-flux γ-ray beam experiments can be conducted effectively.

120

Theoretically, copper-niobium(Cu-Nb) composite superconducting cavities have excellent potential for high thermal and mechanical stability. They can appropriately exploit the high-gradient surface processing recipes developed for the bulk niobium (Nb) cavity and the thick copper (Cu) layer's high thermal conductivity and rigidity, thereby enhancing the operational stability of the bulk Nb cavities. This study conducted a global review of the technical approaches employed for fabricating Cu-Nb composite superconducting cavities. We explored Cu-Nb superconducting cavities based on two technologies at the Institute of Modern Physics, Chinese Academy of Sciences (IMP, CAS), including their manufacturing processes, radio frequency (RF) characteristics, and mechanical performance. These cavities exhibit robust mechanical stability. First, the investigation of several 1.3 GHz single-cell elliptical cavities using the Cu-Nb composite sheets indicated that the wavy structure at the Cu-Nb interface influenced the reliable welding of the Cu-Nb composite parts. We observed the generation and trapping of magnetic flux density during the T_c crossing of Nb in cooldown process. The cooling rates during the T_c-crossing of Nb exerted a substantial impact on the performance of the cavities. Furthermore, we measured and analyzed the surface resistance R_s attributed to the trapped magnetic flux induced by the Seebeck effect after quenching events. Second, for the first time, a low-beta bulk Nb cavity was plated with Cu on its outer surface using electroplating technology. We achieved a high peak electric field E_pk of ~ 88.8 MV/m at 2 K and the unloaded quality factor Q₀ at the E_pk of 88.8 MV/m exceeded 1×10¹⁰. This demonstrated that the electroplating Cu on the bulk Nb cavity is a practical method of developing the Cu–Nb composite superconducting cavity with superior thermal stability. The results presented here provide valuable insights for applying Cu-Nb composite superconducting cavities in superconducting accelerators with stringent operational stability requirements.

109

Lithium- and manganese-rich (LMR) oxide cathode materials are among the most attractive candidates for next-generation energy-storage materials owing to their anomalous capacity. However, severe Mn dissolution that occurs during long-term cycling, which leads to capacity loss, hinders their application prospects. In this study, nanoscale AlPO₄-coated Li_1.2Ni_0.13Co_0.13Mn_0.54O₂ (LMR@APO) with significantly enhanced electrochemical performance is successfully synthesized using a simple and effective sol-gel method to mitigate Mn dissolution and suppress local structural distortion at high voltages. Because of the complex evolution of the structure and oxidation state of LMR materials during electrochemical cycling, observing and analyzing them using traditional single characterization methods may be difficult. Therefore, we combine various synchrotron-based characterization techniques to conduct a detailed analysis of the electronic and coordination structures of the cathode material from the surface to the bulk. Synchrotron-based hard- and soft-X-ray spectroscopies are integrated to investigate the differences in O and Mn evolution between the surfaces and bulk of the cathode. Advanced synchrotron-based transmission X-ray microscopy combined with X-ray near-edge absorption-structure technology is utilized to visualize the two-dimensional nanometer-scale reactivity of the LMR cathode. The AlPO₄-coating layer can stabilize the surface structure of the LMR material, effectively alleviating irreversible oxygen release on the surface and preventing the dissolution of Mn²⁺ at the interface caused by side reactions after a long cycle. Therefore, the spatial reaction uniformity of Mn is enhanced by the AlPO₄-coating layer, and rapid capacity decay caused by Mn deactivation is prevented. The AlPO₄-coating method is a facile modification strategy for high-performance LMR materials.

With the rapid development of nuclear energy, the removal of radioactive iodine generated during spent-fuel reprocessing has become increasingly important. Based on the unique straw-like structure of populus tomentosa fiber (PTF) and the highly active iodine vapor capture ability of zero-valent silver nanoparticles (PTF@Ag⁰NP), an Ag⁰NP composite functional material with highly efficient iodine vapor capture capability was synthesized from biowaste PTF through ultrasonic and high-temperature hydrothermal methods in this study. The iodine capture experiment demonstrated that PTF@Ag⁰NP exhibits rapid iodine capture efficiency, reaching dynamic equilibrium within 4 h and a maximum capture capacity of 1008.1 mg/g. Density functional theory calculations show that PTF@Ag⁰NP exhibits extremely high chemical reactivity towards iodine, with a reaction binding energy of -2.88 eV. Additionally, the molecular dynamics of PTF@Ag⁰NP indicate that there is no atomic displacement at 77 ℃, indicating the excellent temperature stability of the material at the operating temperature. The capture mechanism suggests that iodine vapor primarily reacts with Ag⁰NP to form AgI, and that the hydroxyl groups in PTF can also effectively capture iodine vapor by adsorption induction. In conclusion, PTF@Ag⁰NP is expected to be an effective candidate adsorbent material for removing radioactive iodine vapor from exhaust gases during spent-fuel reprocessing.

100

The operational lifespan of nuclear graphite is significantly affected by irradiation creep, yet the microstructural mechanism underlying this creep phenomenon remains unclear. Some theories attempt to link microstructural evolution with creep behavior, but the rapid migration rate of defects under irradiation and loading makes it difficult to capture the specific evolution process experimentally, resulting in a lack of direct structural evidence. Therefore, in this study, molecular dynamics simulations are employed to investigate the irradiation behavior and microstructural migration under external loading. The aim is to provide microstructural evidence for theories such as the dislocation pinning-unpinning and crystal yielding. The results demonstrate that high tensile loads can increase the potential energy and reduces threshold displacement energy of graphite crystals. Consequently, displacement damage probability and creep rate increase, which is not considered in previous theories. Meanwhile, different creep mechanisms are observed at different damage states and applied loads. In low-dose damage states dominated by interstitials and vacancies, the pinning-unpinning process at basal plane may be caused by a defect diffusion mode. Under high stress levels, direct breaking of pinning structures occurs, leading to rapid migration of basal planes, demonstrating the microstructural evolution process of irradiated cyrstal yielding and plastic flow. In high-dose damage states characterized significantly by amorphous components, short-range atomic diffusion can become the dominant creep mechanism, and diffusion along the c-axis of graphite crystals is no longer constrained. These findings provide a crucial reference for understanding the irradiation and creep behavior of nuclear graphite in reactors.

115