Vol.35,

The layout and characteristics of the hard X-ray spectroscopy beamline (BL11B) at the Shanghai Synchrotron Radiation Facility are described herein. BL11B is a bending-magnet beamline dedicated to conventional and millisecond-scale quick-scanning X-ray absorption fine structures. It is equipped with a cylindrical collimating mirror, a double-crystal monochromator comprising Si(111) and Si(311), a channel-cut quick-scanning Si(111) monochromator, a toroidal focusing mirror, and a high harmonics rejection mirror. It can provide 5–30 keV of X-rays with a photon flux of ~5 × 10¹¹ photons/s and an energy resolution of ~ 1.31 × 10^-4 at 10 keV. The performance of the beamline can satisfy the demands of users in the fields of catalysis, materials, and environmental science. This paper presents an overview of the beamline design and a detailed description of its performance and capabilities.

862

The Ultrahard X-ray Multifunctional Application Beamline (BL12SW) is a Phase-II Beamline Project at the Shanghai Synchrotron Radiation Facility. The primary X-ray techniques used at the beamline are high-energy X-ray diffraction and imaging using white and monochromatic light. The main scientific objectives of ultrahard X-ray beamlines are focused on two research areas. One is the study of the structural properties of Earth's interior and new materials under extreme high-temperature and high-pressure conditions, and the other is the characterization of materials and processes in near-real service environments. The beamline utilizes a superconducting wiggler as the light source, with two diamond windows and SiC discs to filter out low-energy light (primarily below 30 keV) and a Cu filter assembly to control the thermal load entering the subsequent optical components. The beamline is equipped with dual monochromators. The first was a meridional bending Laue monochromator cooled by liquid nitrogen, achieving a full-energy coverage of 30–162 keV. The second was a sagittal bending Laue monochromator installed in an external building, providing a focused beam in the horizontal direction with an energy range of 60–120 keV. There were four experimental hutches: two large volume press experimental hutches (LVP1 and LVP2) and two engineering material experimental hutches (ENG1 and ENG2). Each hutch was equipped with various near-real service conditions to satisfy different requirements. For example, LVP1 and LVP2 were equipped with a 200-ton DDIA press and a 2000-ton dual-mode (DDIA and Kawai) press, respectively. ENG1 and ENG2 provide in-situ tensile, creep, and fatigue tests as well as high-temperature conditions. Since June 2023, the BL12SW has been in trial operation. It is expected to officially open to users by early 2024.

969

The utilization of a proton beam from the China Spallation Neutron Source (CSNS) for producing medical radioisotopes is appealing owing to its high current intensity and high energy. The medical isotope production based on the proton beam at the CSNS is significant for the development of future radiopharmaceuticals, particularly for the α-emitting radiopharmaceuticals. The production yield and activity of typical medical isotopes were estimated using the FLUKA simulation. The results indicate that the 300-MeV proton beam with a power of 100 kW at CSNS-II is highly suitable for proof-of-principle studies of most medical radioisotopes. In particular, this proton beam offers tremendous advantages for the large-scale production of alpha radioisotopes, such as ²²⁵Ac, whose theoretical production yield can reach approximately 57 Ci/week. Based on these results, we provide perspectives on the use of CSNS proton beams to produce radioisotopes for medical applications.

789

Transverse mode-coupling instability (TMCI) is a dangerous transverse single-bunch instability that can lead to severe particle loss. The mechanism of TMCI can be explained by the coupling of transverse coherent oscillation modes owing to the transverse short-range wakefield (i.e., the transverse broadband impedance). Recent studies on future circular colliders, e.g., FCC-ee, showed that the threshold of TMCI decreased significantly when both longitudinal and transverse impedances were included. We performed computations for the circular electron-positron collider (CEPC) and observed a similar phenomenon. Systematic studies on the influence of longitudinal impedance on the TMCI threshold were conducted. We concluded that the imaginary part of the longitudinal impedance, which caused a reduction in the incoherent synchrotron tune, was the primary reason for the reduction in the TMCI threshold. Additionally, the real part of the longitudinal impedance assists in increasing the TMCI threshold.

667

The safety assessment of high-level radioactive waste repositories requires a high predictive accuracy for radionuclide diffusion and a comprehensive understanding of the diffusion mechanism. In this study, a through-diffusion method and six machine-learning methods were employed to investigate the diffusion of ReO₄^-, HCrO4−, and I^- in saturated compacted bentonite under different salinities and compacted dry densities. The machine-learning models were trained using two datasets. One dataset contained six input features and 293 instances obtained from the diffusion database system of the Japan Atomic Energy Agency (JAEA-DDB) and 15 publications. The other dataset, comprising 15,000 pseudo-instances, was produced using a multi-porosity model and contained eight input features. The results indicate that the former dataset yielded a higher predictive accuracy than the latter. Light gradient-boosting exhibited a higher prediction accuracy (R² = 0.92) and lower error (MSE = 0.01) than the other machine-learning algorithms. In addition, Shapley Additive Explanations, Feature Importance, and Partial Dependence Plot analysis results indicate that the rock capacity factor and compacted dry density had the two most significant effects on predicting the effective diffusion coefficient, thereby offering valuable insights.

686

Aluminum is the primary structural material in nuclear engineering, and its cross-section induced by 14 MeV neutrons is of great significance. To address the issue of insufficient accuracy for the ²⁷Al(n,2n)²⁶Al reaction cross-section, the activation method and accelerator mass spectrometry (AMS) technique were used to determine the ²⁷Al(n,2n)²⁶Al cross-section, which could be used as a D-T plasma ion temperature monitor in fusion reactors. At the China Academy of Engineering Physics (CAEP), neutron activation was performed using a K-400 neutron generator produced by the T(d,n)⁴He reaction. The ²⁶Al/²⁷Al isotope ratios were measured using the newly installed GYIG 1 MV AMS at the Institute of Geochemistry, Chinese Academy of Sciences. The neutron flux was monitored by measuring the activity of ^{92 m}Nb produced by the ⁹³Nb(n,2n)^{92 m}Nb reaction. The measured results were compared with available data in the experimental nuclear reaction database, and the measured values showed a reasonable degree of consistency with partially available literature data. The newly acquired cross-sectional data at 12 neutron energy points through systematic measurements clarified the divergence, which has two different growth trends from the existing experimental values. The obtained results are also compared with the corresponding evaluated database, and the newly calculated excitation functions with TALYS-1.95 and EMPIRE-3.2 codes, the agreement with CENDL-3.2, TENDL-2021 and EMPIRE-3.2 results are generally acceptable. A substantial improvement in the knowledge of the ²⁷Al(n,2n)²⁶Al reaction excitation function was obtained in the present work, which will lay the foundation for the diagnosis of the fusion ion temperature, testing of the nuclear physics model, and evaluation of nuclear data, etc.

859

Based on the dinuclear system model, the calculated evaporation residue cross sections matched well with the current experimental results. The synthesis of superheavy elements Z=121 was systematically studied through combinations of stable projectiles with Z = 21–30 and targets with half-lives exceeding 50 d. The influence of mass asymmetry and isotopic dependence on the projectile and target nuclei was investigated in detail. The reactions ²⁵⁴Es (⁴⁶Ti, 3n) ²⁹⁷121 and ²⁵²Es (⁴⁶Ti, 3n) ²⁹⁵121 were found to be experimentally feasible for synthesizing superheavy element Z = 121, with maximal evaporation residue cross sections of 6.619 and 4.123 fb at 219.9 and 223.9 MeV, respectively.

381

The study of nuclide production and its properties in the N=126 neutron-rich region is prevalent in nuclear physics and astrophysics research. The upcoming High-energy FRagment Separator (HFRS) at the High-Intensity heavy-ion Accelerator Facility (HIAF), an in-flight separator at relativistic energies, is characterized by high beam intensity, large ion-optical acceptance, high magnetic rigidity, and high momentum resolution power. This provides an opportunity to study the production and properties of neutron-rich nuclei around N=126. In this paper, an experimental scheme is proposed to produce neutron-rich nuclei around N=126 and simultaneously measure their mass and lifetime based on the HFRS separator; the feasibility of this scheme is evaluated through simulations. The results show that under the high-resolution optical mode, many new neutron-rich nuclei approaching the r-process abundance peak around A=195 can be produced for the first time, and many nuclei with unknown masses and lifetimes can be produced with high statistics. Using the time-of-flight corrected by the measured dispersive position and energy loss information, the cocktails produced from ²⁰⁸Pb fragmentation can be unambiguously identified. Moreover, the masses of some neutron-rich nuclei near N=126 can be measured with high precision using the time-of-flight magnetic rigidity technique. This indicates that the HIAF-HFRS facility has the potential for the production and property research of neutron-rich nuclei around N=126, which is of great significance for expanding the chart of nuclides, developing nuclear theories, and understanding the origin of heavy elements in the universe.

647

Neutron-skin thickness is a key parameter for a neutron-rich nucleus; however, it is difficult to determine. In the framework of the Lanzhou Quantum Molecular Dynamics (LQMD) model, a possible probe for the neutron-skin thickness (δ_np) of neutron-rich ⁴⁸Ca was studied in the 140A MeV ⁴⁸Ca + ⁹Be projectile fragmentation reaction based on the parallel momentum distribution (p∥) of the residual fragments. A Fermi-type density distribution was employed to initiate the neutron density distributions in the LQMD simulations. A combined Gaussian function with different width parameters for the left side (Γ_L) and the right side (Γ_R) in the distribution was used to describe the p∥ of the residual fragments. Taking neutron-rich sulfur isotopes as examples, Γ_L shows a sensitive correlation with δ_np of ⁴⁸Ca, and is proposed as a probe for determining the neutron skin thickness of the projectile nucleus.

786

Gao-Long Zhang，Zhen-Wei Jiao，Guang-Xin Zhang，E. N. Cardozo，B. Paes，Shi-Peng Hu，Jian-Qiang Qian，Daniele Mengoni，Wei-Wei Qu，Cong-Bo Li，Yun Zheng，Huan-Qiao Zhang，Hui-Bin Sun，Nan Wang，Chun-Lei Zhang，J. J. Valiente-Dobón，D. Testov，M. Mazzocco，A. Gozzelino，C. Parascandolo，D. Pierroutsakou，M. La Commara，A. Goasduff，D. Bazzacco，D. R. Napoli，F. Galtarossa，F. Recchia，A. Illana，S. Bakes，I. Zanon，S. Aydin，G. de Angelis，M. Siciliano，R. Menegazzo，S. M. Lenzi，S. Akkoyun，L. F. Canto，J. Lubian

One-neutron stripping process between ⁶Li and ²⁰⁹Bi was studied at 28, 30, and 34 MeV using the in-beam γ-ray spectroscopy method. The γ-γ coincident analysis clearly identified two γ-rays feeding the ground and long-lived isomeric states, which were employed to determine the cross section. The one-neutron stripping cross sections were similar to the cross sections of complete fusion in the ⁶Li+²⁰⁹Bi system, but the one-neutron stripping cross sections decreased more gradually at the sub-barrier region. A coupled-reaction-channel calculation was performed to study the detailed reaction mechanism of the one-neutron stripping process in ⁶Li. The calculations indicated that the first excited state of ⁵Li is critical in the actual one-neutron transfer mechanism, and the valence proton of ²⁰⁹Bi can be excited to the low-lying excited state in (⁶Li,⁵Li) reaction, unlike in the (d,p) reaction.

675

Reliable calculations of nuclear binding energies are crucial for advancing the research of nuclear physics. Machine learning provides an innovative approach to exploring complex physical problems. In this study, the nuclear binding energies are modeled directly using a machine-learning method called the Gaussian process. First, the binding energies for 2238 nuclei with Z > 20 and N > 20 are calculated using the Gaussian process in a physically motivated feature space, yielding an average deviation of 0.046 MeV and a standard deviation of 0.066 MeV. The results show the good learning ability of the Gaussian process in the studies of binding energies. Then, the predictive power of the Gaussian process is studied by calculating the binding energies for 108 nuclei newly included in AME2020. The theoretical results are in good agreement with the experimental data, reflecting the good predictive power of the Gaussian process. Moreover, the α-decay energies for 1169 nuclei with 50≤Z≤110 are derived from the theoretical binding energies calculated using the Gaussian process. The average deviation and the standard deviation are, respectively, 0.047 MeV and 0.070 MeV. Noticeably, the calculated α-decay energies for the two new isotopes ²⁰⁴Ac [M. H. Huang et al. Phys. Lett. B 834, 137484 (2022)] and ²⁰⁷Th [H. B. Yang et al. Phys. Rev. C 105, L051302 (2022)] agree well with the latest experimental data. These results demonstrate that the Gaussian process is reliable for the calculations of nuclear binding energies. Finally, the α-decay properties of some unknown actinide nuclei are predicted using the Gaussian process. The predicted results can be useful guides for future research on binding energies and α-decay properties.

796

The recently discovered, extremely proton-rich nuclide ¹⁸Mg exhibits ground-state decay via two sequential two-proton (2p) emissions through the intermediate nucleus, ¹⁶Ne. This study investigates the structure and the initial 2p decay mechanism of ¹⁸Mg by examining the density and correlations of the valence protons using a three-body Gamow-coupled-channel method. The results show that the ground state of ¹⁸Mg is significantly influenced by the continuum, resulting in a significant s-wave component. However, based on the current framework, this does not lead to a significant deviation in mirror symmetry in either the structure or spectroscopy of the ¹⁸Mg-¹⁸C pair. Additionally, the time evolution analysis of the ¹⁸Mg ground state suggests a simultaneous 2p emission during the first step of decay. The observed nucleon–nucleon correlations align with those of the light-mass 2p emitters, indicating a consistent decay behavior within this nuclear region.

325

Relativistic isobar (4496Ru+4496Ru and 4096Zr+4096Zr) collisions have revealed intricate differences in their nuclear size and shape, inspiring unconventional studies of nuclear structure using relativistic heavy ion collisions. In this study, we investigate the relative differences in the mean multiplicity (R〈Nch〉) and the second- (Rϵ2) and third-order eccentricity (Rϵ3) between isobar collisions using initial state Glauber models. It is found that initial fluctuations and nuclear deformations have negligible effects on R〈Nch〉 in most central collisions, while both are important for the Rϵ2 and Rϵ3, the degree of which is sensitive to the underlying nucleonic or sub-nucleonic degree of freedom. These features, compared to real data, may probe the particle production mechanism and the physics underlying nuclear structure.

612

The superconducting magnet system of a fusion reactor plays a vital role in plasma confinement, a process that can be disrupted by various operational factors. A critical parameter for evaluating the temperature margin of superconducting magnets during normal operation is the nuclear heating caused by D-T neutrons. This study investigates the impact of nuclear heating on a superconducting magnet system by employing an improved analysis method that combines neutronics and thermal hydraulics. In the magnet system, toroidal field (TF) magnets are positioned closest to the plasma and bear the highest nuclear-heat load, making them prime candidates for evaluating the influence of nuclear heating on stability. To enhance the modeling accuracy and facilitate design modifications, a parametric TF model that incorporates heterogeneity is established to expedite the optimization design process and enhance the accuracy of the computations. A comparative analysis with a homogeneous TF model reveals that the heterogeneous model improves accuracy by over 12%. Considering factors such as heat load, magnetic-field strength, and cooling conditions, the cooling circuit facing the most severe conditions is selected to calculate the temperature of the superconductor. This selection streamlines the workload associated with thermal-hydraulic analysis. This approach enables a more efficient and precise evaluation of the temperature margin of TF magnets. Moreover, it offers insights that can guide the optimization of both the structure and cooling strategy of superconducting magnet systems.

625

Cs and I can migrate through fuel-cladding interfaces and accelerate the cladding corrosion process induced by the fuel-cladding chemical interaction. Cr coating has emerged as an important candidate for mitigating this chemical interaction. In this study, first-principles calculations were employed to investigate the diffusion behavior of Cs and I in the Cr bulk and grain boundaries to reveal the microscopic interaction mitigation mechanisms at the fuel-cladding interface. The interaction between these two fission products and the Cr coating were studied systematically, and the Cs and I temperature-dependent diffusion coefficients in Cr were obtained using Bocquet’s oversized solute-atom model and Le Claire’s nine-frequency model, respectively. The results showed that the Cs and I migration barriers were significantly lower than that of Cr, and the Cs and I diffusion coefficients were more than three orders of magnitude larger than the Cr self-diffusion coefficient within the temperature range of Generation-IV fast reactors (below 1000 K), demonstrating the strong penetration ability of Cs and I. Furthermore, Cs and I are more likely to diffuse along the grain boundary because of the generally low migration barriers, indicating that the grain boundary serves as a fast diffusion channel for Cs and I.

779

Small-break superposed station blackout (SBO) accidents are the basic design accidents of nuclear power plants. Under the condition of a small break in the cold leg, SBO further increases the severity of the accident, and the steam bypass discharging system (GCT) in the second circuit can play an important role in guaranteeing core safety. To explore the influence of the GCT on the thermal-hydraulic characteristics of the primary circuit, RELAP5 software was used to establish a numerical model based on a typical pressurized water reactor (PWR) nuclear power plant. Five different small breaks in the cold-leg superposed SBO were selected, and the impact of the GCT operation on the transient response characteristics of the primary and secondary circuit systems was analyzed. The results show that the GCT plays an indispensable role in core heat removal during an accident; otherwise, core safety cannot be guaranteed. The GCT was used in conjunction with the primary safety injection system during the placement process. When the break diameter was greater than a certain critical value, the core cooling rate could not be guaranteed to be less than 100 K/h; however, the core remained in a safe state.

617

The heavy-water-moderated molten-salt reactor (HWMSR) is a newly proposed reactor concept, in which heavy water is adopted as the moderator and molten salt dissolved with fissile and fertile elements is used as the fuel. Issues arising from graphite in traditional molten-salt reactors, including the positive temperature coefficient and management of highly radioactive spent graphite waste, can be addressed using the HWMSR. Until now, research on the HWMSR has been centered on the core design and nuclear-fuel cycle to explore the viability of the HWMSR and its advantages in fuel utilization. However, the core safety of the HWMSR has not been extensively studied. Therefore, we evaluate typical accidents in a small modular HWMSR, including fuel-salt inlet temperature-overcooling and -overheating accidents, fuel-salt inlet flow-rate decrease, heavy-water inlet temperature-overcooling accidents, and heavy-water inlet mass flow-rate decrease accidents, based on a neutronics and thermal-hydraulics coupled code. The results demonstrated that the core maintained safety during the investigated accidents.

651

Carbon-based nanomaterials have important research significance in various disciplines, such as composite materials, nanoelectronic devices, biosensors, biological imaging, and drug delivery. Recently, the human and ecological risks associated with carbon-based nanomaterials have received increasing attention. However, the biosafety of carbon-based nanomaterials has not been investigated extensively. In this study, we used different types of carbon materials, namely, graphene oxide (GO), single-walled carbon nanotubes (SWCNTs), and multiwalled carbon nanotubes (MWCNTs), as models to observe their distribution and oxidative damage in vivo. The results of Histopathological and ultrastructural examinations indicated that the liver and lungs were the main accumulation targets of these nanomaterials. SR-μ-XRF analysis revealed that SWCNTs and MWCNTs might be present in the brain. This shows that the three types of carbon-based nanomaterials could cross the gas–blood barrier and eventually reach the liver tissue. In addition, SWCNTs and MWCNTs could cross the blood–brain barrier and accumulate in the cerebral cortex. The increase in ROS and MDA levels and the decrease in GSH, SOD, and CAT levels indicated that the three types of nanomaterials might cause oxidative stress in the liver. This suggests that direct instillation of these carbon-based nanomaterials into rats could induce ROS generation. In addition, iron (Fe) contaminants in these nanomaterials were a definite source of free radicals. However, these nanomaterials did not cause obvious damage to the rat brain tissue. The deposition of selenoprotein in the rat brain was found to be related to oxidative stress and Fe deficiency. This information may support the development of secure and reasonable applications of the studied carbon-based nanomaterials.

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