Vol.35,

A new muon beam facility, called the Experimental Muon Source (EMuS), was proposed for construction at the China Spallation Neutron Source (CSNS). The design of the complex muon beamlines for the EMuS baseline scheme, which is based on superconducting solenoids, superferric dipoles and room-temperature magnets, is presented herein. Various muon beams, including surface muons, decay muons and low-energy muons, have been developed for multipurpose applications. The optics design and simulation results of the trunk beamline and branch beamlines are presented. With a proton beam power of 25 kW at a standalone target station that consists of a conical graphite target and high-field superconducting solenoids, the muon beam intensity in the trunk beamline varies from 10⁷/s for surface muons to 10¹⁰/s for high-momentum decay muons. And at the endstations, these values vary from 10⁵/s for surface muons to 10⁸/s for decay muons.

671

Very high-energy electrons (VHEE) are potential candidates for FLASH radiotherapy for deep-seated tumors. We proposed a compact VHEE facility based on an X-band high-gradient high-power technique. In this study, we investigated and realized the first X-band backward traveling wave (BTW) accelerating structure as the buncher for a VHEE facility. A method for calculating the parameters of single cells from the field distribution was introduced to simplify the design of the BTW structure. Time-domain circuit equations were applied to calculate the transient beam parameters of the buncher in the unsteady state. A prototype of the BTW structure with a thermionic-cathode diode electron gun was designed, fabricated, and tested at high power at the Tsinghua X-band High-power test stand. The structure successfully operated with 5-MW microwave pulses from the pulse compressor and outputted electron bunches with an energy of 8 MeV and a pulsed current of 108 mA.

611

Charge strippers play an essential role in heavy-ion accelerators by stripping the projectile ions to higher charge states to enhance the acceleration efficiency downstream of the stripper. In the high-energy mode of the booster ring (BRing) of the high-intensity heavy-ion accelerator facility, the pre-accelerated ions from the iLinac will be stripped by a carbon foil to higher charge states and then injected into the BRing. The key parameters of the stripper and stripped ions were calculated, and the influence of stripping on the beam quality was discussed. To get high stripping efficiencies, the foil thicknesses and resultant charge state distributions for the typical ions were determined by the code ETACHA. The equilibrium thickness was obtained for the U beam, while the stripper thicknesses for the Xe and Kr beams were determined based on a compromise between the stripped charge states and the stripping efficiency. The energy loss, energy straggling, and emittance growth due to stripping have a non-negligible impact on the transport of the stripped beams and the injection of the ring. Therefore, these parameters were simulated by GEANT4. In addition, the foil’s temperature evolution, which greatly affects the foil lifetime, was simulated by ANSYS. The maximum temperature of the foil bombarded by the U and Xe beams with the nominal parameters will exceed the safe value in terms of the impact of evaporation on the foil’s lifetime. Given the foil temperature constraint, the highest tolerable beam intensity and the injected ion number into the ring were derived for different beam sizes. The results of this paper will present important reference data for the optimization design and commissioning of the beamline and injection to the BRing for the stripped ions.

607

The rise in breast cancer diagnoses among Chinese women has necessitated the use of X-ray breast screening, which carries a radiation risk. This study aimed to provide a dosimetry protocol for the Chinese female population to replace the traditional standard that utilizes simplified breast models, for the accurate estimation of the mean glandular dose of a patient undergoing digital breast tomosynthesis (DBT). The first set of detailed Chinese female breast models and representative breast parameters was constructed. Considering backscatter radiation and computational efficiency, we improved the combination of these models and the Chinese reference adult female whole-body voxel phantom. Image acquisition for four commercial DBT systems that are widely employed in China was simulated using the Monte Carlo method to obtain the normalized glandular dose coefficients of DBT (DgNDBT) and the glandular depth dose (Dgdep(z)) for different breast characteristics and X-ray spectra. We calculated a series of DgNDBT values for breasts with different percentage mass glandularities (5%, 25%, 50%, 75%, and 100%) and compressed breast thicknesses (2, 3, 4, 5, 6, and 7 cm) at various tube potentials (25, 28, 30, 32, 35, and 49 kV) and target/filter combinations (W/Rh, W/Al, Mo/Mo, Rh/Rh, and Rh/Ag). The parameter dependence of the breast characteristics and beam conditions on DgNDBT in detailed breast models was investigated. The DgNDBT results were 14.6-51.0% lower than those of the traditional dosimetry standard in China. The difference in DgNDBT was mainly due to a decrease in the depth of the main energy deposition area caused by the glandular distribution along the depth direction. The results obtained in this study may be used to improve breast dosimetry in China and provide more detailed information on risk assessment during DBT.

922

POLAR-2 is a gamma-ray burst (GRB) polarimeter that is designed to study the polarization in GRB radiation emissions, aiming to improve our knowledge of related mechanisms. POLAR-2 is expected to utilize an on-board polarimeter that is sensitive to soft X-rays (2-10 keV), called low-energy polarization detector (LPD). We have developed a new soft X-ray polarization detector prototype based on gas microchannel plates (GMCPs) and pixel chips (Topmetal). The GMCPs have bulk resistance, which prevents charging-up effects and ensures gain stability during operation. The detector is composed of low-outgassing materials and is gas-sealed using a laser welding technique, ensuring long-term stability. A modulation factor of 41.28% ± 0.64% is obtained for a 4.5 keV polarized X-ray beam. A residual modulation of 1.96% ± 0.58% at 5.9 keV is observed for the entire sensitive area.

510

High-purity germanium (HPGe) detectors, which are used for direct dark matter detection, have the advantages of a low threshold and excellent energy resolution. The surface passivation of HPGe has become crucial for achieving an extremely low energy threshold. In this study, first-principles simulations, passivation film preparation, and metal oxide semiconductor (MOS) capacitor characterization were combined to study surface passivation. Theoretical calculations of the energy band structure of the -H,-OH, and -NH₂ passivation groups on the surface of Ge were performed, and the interface state density and potential with five different passivation groups with N/O atomic ratios were accurately analyzed to obtain a stable surface state. Based on the theoretical calculation results, the surface passivation layers of the Ge₂ON₂ film were prepared via magnetron sputtering in accordance with the optimum atomic ratio structure. The microstructure, C-V, and I-V electrical properties of the layers, and the passivation effect of the Al/Ge₂ON₂/Ge MOS were characterized to test the interface state density. The mean interface state density obtained by the Terman method was 8.4 × 10¹¹ cm^-2 eV^-1. The processing of germanium oxynitrogen passivation films is expected to be used in direct dark matter detection of the HPGe detector surface passivation technology to reduce the detector leakage currents.

569

Currently, with the advent of high-repetition-rate laser-plasma experiments, the demand for online diagnosis for the X-ray spectrum is increasing because the laser-plasma-generated X-ray spectrum is very important for characterizing electron dynamics and applications. In this study, scintillators and silicon PIN (P-type-Intrinsic-N-type semiconductor) diodes were used to construct a wideband online filter stack spectrometer. The X-ray sensor and filter arrangement was optimized using a genetic algorithm to minimize the condition number of the response matrix. Consequently, the unfolding error was significantly reduced based on numerical experiments. The detector responses were quantitatively calibrated by irradiating the scintillator and PIN diode with various nuclides and comparing the measured γ-ray peaks. A prototype 15-channel spectrometer was developed by integrating an X-ray detector with front- and back-end electronics. The prototype spectrometer could record X-ray pulse signals at a repetition rate of 1 kHz. Furthermore, an optimized spectrometer was employed to record the real-time spectra of laser-driven bremsstrahlung sources. This optimized spectrometer offers a compact solution for spectrum diagnostics of ultrashort X-ray pulses, exhibiting improved accuracy in terms of spectrum measurements and repetition rates, and could be widely used in next-generation high-repetition-rate high-power laser facilities.

862

Various electromagnetic signals are excited by the beam in the acceleration and beam-diagnostic elements of a particle accelerator. It is important to obtain time-domain waveforms of these signals with high temporal resolution for research, such as the study of beam-cavity interactions and bunch-by-bunch parameter measurements. Therefore, a signal reconstruction algorithm with ultrahigh spatiotemporal resolution and bunch phase compensation based on equivalent sampling is proposed in this paper. Compared with traditional equivalent sampling, the use of phase compensation and setting the bunch signal zero-crossing point as the time reference can construct a more accurate reconstructed signal. The basic principles of the method, simulation, and experimental comparison are also introduced. Based on the beam test platform of the Shanghai Synchrotron Radiation Facility (SSRF) and the method of experimental verification, the factors that affect the reconstructed signal quality are analyzed and discussed, including the depth of the sampled data, quantization noise of analog-to-digital converter (ADC), beam transverse oscillation, and longitudinal oscillation. The results of the beam experiments show that under the user operation conditions of the Shanghai Synchrotron Radiation Facility (SSRF), a beam excitation signal with an amplitude uncertainty of 2% can be reconstructed.

526

In nuclear reactors, temperature fluctuations of fluids may cause fatigue damage to adjacent structures; this is referred to as thermal striping. Research on thermal striping in the upper plenum has mainly focused on fluid fields. Few experimental studies have been reported on solid structures in a fluid field with a coaxial jet. This study entailed an experimental study of the temperature fluctuations in the fluid and on a plate surface caused by a coaxial jet. The temperature fluctuations of the fluid and plate surfaces located at different heights were analyzed. The cause of the temperature fluctuation was analyzed using a transient temperature distribution. The results show that the mixing of the hot and cold fluids gradually becomes uniform in the positive axial direction. The average surface temperatures tended to be consistent. When the jet reaches the plate surface, the swing of the jet center, contraction and expansion of the cold jet, and changes in the jet shape result in temperature fluctuations. The intensity of the temperature fluctuation was affected by the position. More attention should be paid when the plate is located at a lower height, and between the hot and cold-fluid nozzles.

509

During the decommissioning of the Fukushima Daiichi nuclear power plant, it is important to consider the retrieval of resolidified debris both in air and underwater configurations. For the subsequent retrieval of debris from the reactor building, the resolidified debris must be cut into smaller pieces using various cutting methods. During the cutting process, aerosol particles are expected to be generated at the submicron scale. It has been noted that such aerosols sizing within the Greenfield gap (0.1-1 μm) are difficult to remove effectively using traditional spraying methods. Therefore, to improve the aerosol removal efficiency of the spray system, a new aerosol agglomeration method was recently proposed, which involves injecting water mist to enlarge the sizes of the aerosol particles before removing them using water sprays. In this study, a series of experiments were performed to clarify the proper spray configurations for effective aerosol scavenging and to improve the performance of the water mist. The experimental results showed that the spray flow rate and droplet characteristics are important factors for the aerosol-scavenging efficiency and performance of the water mist. The results obtained from this study will be helpful for the optimization of the spray system design for effective aerosol scavenging during the decommissioning of the Fukushima Daiichi plant.

813

The aging of operational reactors leads to increased mechanical vibrations in the reactor interior. The vibration of the in-core sensors near their nominal locations is a new problem for neutronic field reconstruction. Current field-reconstruction methods fail to handle spatially moving sensors. In this study, we propose a Voronoi tessellation technique in combination with convolutional neural networks to handle this challenge. Observations from movable in-core sensors were projected onto the same global field structure using Voronoi tessellation, holding the magnitude and location information of the sensors. General convolutional neural networks were used to learn maps from observations to the global field. The proposed method reconstructed multi-physics fields (including fast flux, thermal flux, and power rate) using observations from a single field (such as thermal flux). Numerical tests based on the IAEA benchmark demonstrated the potential of the proposed method in practical engineering applications, particularly within an amplitude of 5 cm around the nominal locations, which led to average relative errors below 5% and 10% in the L₂ and L_∞ norms, respectively.

765

Ferritic/martensitic (F/M) steel is widely used as a structural material in thermal and nuclear power plants. However, it is susceptible to intergranular damage, which is a critical issue, under service conditions. In this study, to improve the resistance to intergranular damage of F/M steel, a thermomechanical process (TMP) was employed to achieve a grain boundary engineering (GBE) microstructure in F/M steel P92. The TMP, including cold-rolling thickness reduction of 6%, 9%, and 12%, followed by austenitization at 1323 K for 40 min and tempering at 1053 K for 45 min, was applied to the as-received (AR) P92 steel. The prior austenite grain (PAG) size, prior austenite grain boundary character distribution (GBCD), and connectivity of prior austenite grain boundaries (PAGBs) were investigated. Compared to the AR specimen, the PAG size did not change significantly. The fraction of coincident site lattice boundaries (CSLBs, 3 ≤ Σ ≤ 29) and Σ3ⁿ boundaries along PAGBs decreased with increasing reduction ratio because the recrystallization fraction increased with increasing reduction ratio. The PAGB connectivity of the 6% deformed specimen slightly deteriorated compared with that of the AR specimen. Moreover, potentiodynamic polarization studies revealed that the intergranular damage resistance of the studied steel could be improved by increasing the fraction of CSLBs along the PAGBs, indicating that the TMP, which involves low deformation, could enhance the intergranular damage resistance.

467

Global variance reduction is a bottleneck in Monte-Carlo shielding calculations. The global variance reduction problem requires that the statistical error of the entire space be uniform. This study proposed a grid-AIS method for the global variance reduction problem based on the AIS method, which was implemented in the Monte Carlo program MCShield. The proposed method was validated using the VENUS-III international benchmark problem and a self-shielding calculation example. The results from the VENUS-III benchmark problem showed that the grid-AIS method achieved a significant reduction in the variance of the statistical errors of the MESH grids, decreasing from 1.08E-02 to 3.84E-03, representing a 64.00% reduction. This demonstrates that the Grid-AIS method is effective in addressing global issues. The results of the self-shielding calculation demonstrate that the grid-AIS method produced accurate computational results. Moreover, the grid-AIS method exhibited a computational efficiency approximately one order of magnitude higher than that of the AIS method and approximately two orders of magnitude higher than that of the conventional Monte Carlo method.

946

Herein, we employ the threshold energy neutron analysis (TENA) technique to introduce the world's first active interrogation system to detect special nuclear materials (SNMs), including U-235 and Pu-239. The system utilizes a DD neutron generator based on inertial electrostatic confinement (IEC) to interrogate suspicious objects. To detect secondary neutrons produced during fission reactions induced in SNMs, a tensioned metastable fluid detector (TMFD) is employed. The current status of the system's development is reported in this paper, accompanied by the results from experiments conducted to detect 10 g of highly enriched uranium (HEU). Notably, the experimental findings demonstrate a distinct difference in the count rates of measurements with and without HEU. This difference in count rates surpasses two times the standard deviation, indicating a confidence level of more than 96% for identifying the presence of HEU. The paper presents and extensively discusses the proof-of-principle experimental results, along with the system's planned trajectory.

542

We proposed and compared three methods (filter burnup, single-energy burnup, and burnup extremum analysis) to build a high-resolution neutronics model for 238Pu production in high-flux reactors. The filter burnup and single-energy burnup methods have no theoretical approximation and can achieve a spectrum resolution of up to ~1 eV, thereby constructing the importance curve and yield curve of the full energy range. The burnup extreme analysis method combines the importance and yield curves to consider the influence of irradiation time on production efficiency, thereby constructing extreme curves. The three curves, which quantify the transmutation rate of the nuclei in each energy region, are of physical significance because they have similar distributions. A high-resolution neutronics model for ²³⁸Pu production was established based on these three curves, and its universality and feasibility were proven. The neutronics model can guide the neutron spectrum optimization and improve the yield of ²³⁸Pu by up to 18.81%. The neutronics model revealed the law of nuclei transmutation in all energy regions with high spectrum resolution, thus providing theoretical support for high-flux reactor design and irradiation production of ²³⁸Pu.

742

The 28 nm process has a high cost-performance ratio and has gradually become the standard for the field of radiation-hardened devices. However, owing to the minimum physical gate length of only 35 nm, the physical area of a standard 6T SRAM unit is approximately 0.16 μm ², resulting in a significant enhancement of multi-cell charge-sharing effects. Multiple-cell upsets (MCUs) have become the primary physical mechanism behind single-event upsets (SEUs) in advanced nanometer node devices. The range of ionization track effects increases with higher ion energies, and spacecraft in orbit primarily experience SEUs caused by high-energy ions. However, ground accelerator experiments have mainly obtained low-energy ion irradiation data. Therefore, the impact of ion energy on the SEU cross-section, charge collection mechanisms, and MCU patterns and quantities in advanced nanometer devices remains unclear. In this study, based on the experimental platform of the Heavy Ion Research Facility in Lanzhou (HIRFL), low- and high-energy heavy-ion beams were used to study the SEUs of 28 nm SRAM devices. The influence of ion energy on the charge collection processes of small-sensitive-volume devices, MCU patterns, and upset cross-sections was obtained, and the applicable range of the inverse-cosine law was clarified. The findings of this study are an important guide for the accurate evaluation of SEUs in advanced nanometer devices and for the development of radiation-hardening techniques.

731

We investigated ^50,52-54Cr-induced fusion reactions for the synthesis of the superheavy element in the 104 ≤ Z ≤ 122 range. The cross-sections produced in this investigation using ⁵⁴Cr projectiles were compared with those obtained in prior experiments. The estimated cross-sections from this analysis are consistent with the findings of prior studies. From the current study, the predicted cross-section was found to be 42fb at 236 MeV for ⁵³Cr+²⁴³Am, 23.2 fb at 236 MeV for ⁵⁴Cr+²⁴⁷Cm, 95.6 fb at 240 MeV for ⁵³Cr+²⁴⁸Bk, and 1.33 fb at 242 MeV for ⁵³Cr+²⁵⁰Cf. Consequently, these projected cross-sections with excitation energy and beam energy will be useful in future Cr-induced fusion reaction investigations.

865

Nuclear mass is a fundamental property of nuclear physics and a necessary input in nuclear astrophysics. Owing to the complexity of atomic nuclei and nonperturbative strong interactions, conventional physical models cannot completely describe nuclear binding energies. In this study, the mass formula was improved by considering an additional term from the Fermi gas model. All nuclear masses in the Atomic Mass Evaluation Database were reproduced with a root-mean-square deviation (RMSD) of ∼1.86 MeV (1.92 MeV). The new mass formula exhibits good performance in the neutron-rich nuclear region. The RMSD decreases to 0.393 MeV when the ratio of the neutron number to the proton number is ≥1.6.

535