Vol.36,

The acquisition of neutron time spectrum data plays a pivotal role in the precise quantification of uranium via prompt fission neutron uranium logging (PFNUL). However, the impact of the detector dead-time effect remains paramount in the accurate acquisition of the neutron time spectrum. Therefore, it is imperative for neutron logging instruments to establish a dead-time correction method that is not only uncomplicated but also practical and caters to various logging sites. This study has formulated an innovative equation for determining dead time and introduced a dead-time correction method for the neutron time spectrum, called the “Dual Flux Method”. Using this approach, a logging instrument captures two neutron time spectrums under disparate neutron fluxes. By carefully selecting specific “windows” on the neutron time spectrum, the dead time can be accurately ascertained. To substantiate its efficacy and discern the influencing factors, experiments were conducted utilizing a deuterium-tritium (D-T) neutron source, a Helium-3 (³He) detector, and polyethylene shielding to collate and analyze the neutron time spectrum under varying neutron fluxes (at high voltages). The findings underscore that the “height” and “spacing” of the two windows are the most pivotal influencing factors. Notably, the “height” (f_d) should surpass 2, and the “spacing” t_wd should exceed 200 μs. The dead time of the ³He detector determined in the experiment was 7.35 μs. After the dead-time correction, the deviation of the decay coefficients from the theoretical values for the neutron time spectrum under varying neutron fluxes decreased from 12.4% to within 5%. Similarly, for the PFNUL instrument, the deviation in the decay coefficients decreased from 22.94% to 0.49% after correcting for the dead-time effect. These results demonstrate the exceptional efficacy of the proposed method in ensuring precise uranium quantification. The dual flux method was experimentally validated as a universal approach applicable to pulsed neutron logging instruments and holds immense significance for uranium exploration.

158

The first 2⁺ excited states of the nucleus directly reflect the interaction between the shell structure and the nucleus, providing insights into the validity of the shell model and nuclear structure characteristics. Although the features of the first 2⁺ excited states can be measured for stable nuclei and calculated using nuclear models, significant uncertainty remains. This study employs a machine-learning model based on a light-gradient boosting machine (LightGBM) to investigate the first 2⁺ excited states. Specifically, the training of the LightGBM algorithm and the prediction of the first 2⁺ properties of 642 nuclei are presented. Furthermore, detailed comparisons of the LightGBM predictions were performed with available experimental data, shell model calculations, and Bayesian neural network predictions. The results revealed that the average difference between the LightGBM predictions and the experimental data was 18 times smaller than that obtained by the shell model and only 70% of the BNN prediction results. Considering Mg, Ca, Kr, Sm, and Pb isotopes as examples, it was also observed that LightGBM can effectively reproduce the magic number mutation caused by shell effects, with the energy being as low as 0.04 MeV due to shape coexistence. Therefore, we believe that leveraging LightGBM-based machine learning can profoundly enhance our insights into nuclear structures and provide new avenues for nuclear physics research.

159

Based on the Skyrme energy density functional and reaction Q-value, this study proposed an effective nucleus-nucleus potential for describing the capture barrier in heavy-ion fusion processes. The 443 extracted barrier heights were well reproduced with a root-mean-square (RMS) error of 1.53 MeV and the RMS deviations with respect to 144 time-dependent Hartree–Fock capture barrier heights was only 1.05 MeV. Coupled with the Siwek–Wilczyński formula, wherein three parameters were determined by the proposed effective potentials, the measured capture cross sections at energies around the barriers were reasonably well reproduced for several fusion reactions induced by nearly spherical nuclei as well as by nuclei with large deformations, such as ¹⁵⁴Sm and ²³⁸U. The shallow capture pockets and small values of the average barrier radii resulted in the reduction of the capture cross sections for ^52,54Cr-and ⁶⁴ Ni-induced reactions, which were related to the synthesis of new super-heavy nuclei.

141

The isospin asymmetry and quadrupole deformation value of drip-line nuclei are investigated using the Weizsäcker–Skyrme nuclear mass formula. We observe that for heavy nuclei at the neutron drip line, the Coulomb energy heightened by an augmented charge could not be mitigated completely by symmetry energy because of isospin asymmetry saturation but is resisted complementally by strong nuclear deformation. The positions of saltation for the difference in proton numbers between two neighboring nuclei at the neutron drip line, and the isospin asymmetry of the neutron drip-line nucleus as a function of the neutron number distinctly correspond to the known magic numbers, which can serve as a reference to verify the undetermined neutron magic number. Through fitting of the binding energy difference between mirror nuclei (BEDbMN), a set of Coulomb energy coefficients with greater accuracy is obtained. A high-precision description of the BEDbMN is useful for accurately determining the experimentally unknown mass of the nucleus close to the proton drip line if the mass of its mirror nucleus is measured experimentally.

119

The isospin splitting of the Dirac mass obtained using the relativistic Brueckner-Hartree-Fock (RBHF) theory was thoroughly investigated. From the perspective in the full Dirac space, the long-standing controversy between the momentum-independent approximation (MIA) method and the projection method on the isospin splitting of the Dirac mass in asymmetric nuclear matter was analyzed in detail. We found that the assumption procedure of the MIA method, which assumes that single-particle potentials are momentum independent, is not a sufficient condition that directly leads to the opposite sign of the isospin splitting of the Dirac mass, whereas the extraction procedure of the MIA method, which extracts single-particle potentials from single-particle potential energy, changes the sign. A formal expression of the Dirac mass was obtained by approximately solving a set of equations involved in the extraction procedure. The opposite isospin splitting of the Dirac mass was mainly caused by the extraction procedure, which forcibly assumed that the momentum dependence of the single-particle potential energy was in a quadratic form, in which the strength was solely determined by a constant scalar potential. Improved understanding of the isospin splitting of the Dirac mass from ab initio calculations could enhance our knowledge of neutron-rich systems, such as exotic nuclei and neutron stars.

125

We present new data on the ⁶³Cu(γ, n) cross section studied using a quasi-monochromatic and energy-tunable γ beam produced at the Shanghai Laser Electron Gamma Source to resolve the long-standing discrepancy between existing measurements and evaluations of this cross section. Using an unfolding iteration method, ⁶³Cu(γ, n) data were obtained with an uncertainty of less than 4%, and the inconsistencies between the available experimental data were discussed. The γ-ray strength function of ⁶³Cu(γ, n) was successfully extracted as an experimental constraint. We further calculated the cross-section of the radiative neutron capture reaction ⁶²Cu(n, γ) using the TALYS code. Our calculation method enables the extraction of (n, γ) cross sections for unstable nuclides.

154

Inelastic collisions are the dominant cause of energy loss in radiotherapy. In the energy range around the Bragg peak, single ionization (SI) and single- electron capture (SC) are the primary inelastic collisions that lead to energy loss. This study employs the Classical Trajectory Monte Carlo method to study the SI and SC processes of H₂O molecules using He²⁺ and C⁶⁺ projectiles in the energy range of 10 keV/u to 10 MeV/u. The total cross sections, single differential cross sections, impact parameter dependence of SI and SC, and fragmentation cross sections were investigated. Results illustrate that the cross-section for SI is the highest when the projectile energy is close to the Bragg peak energy. When the projectile energy is below the Bragg peak energy, the ionized electrons in the forward direction dominate, and the removal of electrons can be associated with large impact parameters. As the projectile energy increases, the emission angle of the electrons gradually transitions from small angles (0°~30°) to large angles (60°~120°), and the removal of electrons is associated with small impact parameters. The energy distributions of the ionized electron are similar when the projectile energy is equal to, below, or above the Bragg peak energy. The fragmentation cross sections after SI and SC in the energy range around the Bragg peak were also estimated.

134

In a recent paper published in Phys. Rev. Lett. 133, 152503 (2024), H. Zhang, T. Li, and X. Wang predicted that modern intense lasers can induce highly nonlinear responses in the ²²⁹Th nucleus for the first time, which is an astonishing effect of light-nucleus interactions. This phenomenon is underpinned by two key factors: (1) the presence of a very low-lying nuclear excited state and (2) a nuclear hyperfine mixing effect that significantly enhances light-nucleus coupling. The resulting highly nonlinear responses facilitate efficient nuclear excitation and enable coherent light emission from the nucleus, resulting in high harmonic generation. ²²⁹Th presents a promising platform for advancements in both laser-nuclear physics and nuclear clock development. The pioneering work by Zhang et al. marks a new frontier in light-matter interactions.

171

In this study, an end-to-end deep learning method is proposed to improve the accuracy of continuum estimation in low-resolution gamma-ray spectra. A novel process for generating the theoretical continuum of a simulated spectrum is established, and a convolutional neural network consisting of 51 layers and more than 10⁵ parameters is constructed to directly predict the entire continuum from the extracted global spectrum features. For testing, an in-house NaI-type whole-body counter is used, and 10⁶ training spectrum samples (20% of which are reserved for testing) are generated using Monte Carlo simulations. In addition, the existing fitting, step-type, and peak erosion methods are selected for comparison. The proposed method exhibits excellent performance, as evidenced by its activity error distribution and the smallest mean activity error of 1.5% among the evaluated methods Additionally, a validation experiment is performed using a whole-body counter to analyze a human physical phantom containing four radionuclides. The largest activity error of the proposed method is -5.1%, which is considerably smaller than those of the comparative methods, confirming the test results. The multiscale feature extraction and nonlinear relation modeling in the proposed method establish a novel approach for accurate and convenient continuum estimation in a low-resolution gamma-ray spectrum. Thus, the proposed method is promising for accurate quantitative radioactivity analysis in practical applications.

139

Jin-Fang Chen，Yue Zong，Xiao-Yun Pu，Sheng-Wang Xiang，Shuai Xing，Zheng Li，Xu-Ming Liu，Yan-Fei Zhai，Xiao-Wei Wu，Yong-Zhou He，Ling-Ling Gong，Ji-Dong Zhang，Shan-Shan Cao，Wen-Ding Fang，Bin-Tuan Zhang，Kai Xu，Yi-Bo Yu，Guang-Hua Chen，Li-Jun Lu，Ya-Wei Huang，Shen-Jie Zhao，Hong-Tao Hou，Zhen-Yu Ma，Ye-Liang Zhao，Xiang Zheng，Jiu-Ce Sun，Sen Sun，Zhi-Qiang Jiang，Yu-Bin Zhao，Meng Zhang，Ying-Bing Yan，Yi-Yong Liu，Qiang Gu，Hai-Xiao Deng，Li-Xin Yin，Dong Wang，Zhen-Tang Zhao

We report the world-leading performance of a 1.3 GHz cryomodule equipped with eight 9-cell superconducting radio-frequency cavities that underwent a medium-temperature furnace baking process. During continuous wave horizontal testing, these cavities achieved unprecedented average intrinsic quality factors of 4.0×10¹⁰ at 20 MV/m and 3.2×10¹⁰ at 29 MV/m, with no instances of field emission. The cryomodule demonstrates near-complete preservation of ultra-high-quality factors and ultra-high accelerating gradients from vertical to horizontal testing, marking a significant milestone in continuous-wave superconducting radio-frequency accelerator technology. This letter presents the cryomodule development experience, including cavity preparation, cryomodule assembly, degaussing, fast cooldown, and performance testing.

134

High-performance MXene-based polymer nanocomposites are well-suited for various industrial applications owing to their excellent mechanical, thermal, and other properties. However, the fabrication of flame-retardant polymer/MXene nanocomposites remains challenging owing to the limited flame-retardant properties of MXene itself. This study prepared a novel MXene@Ag@PA hybrid material via radiation modification and complexation reaction. This material was used to further enhance the key properties of ethylene vinyl acetate (EVA), such as its mechanical properties, thermal conductivity, flame retardancy and electromagnetic shielding. The addition of two parts of this hybrid material increased the thermal conductivity of EVA by 44.2% and reduced its peak exothermic rate during combustion by 30.1% compared with pure EVA. The material also significantly reduced smoke production and increased the residue content. In the X-band, the electromagnetic shielding effectiveness of the EVA composites reached 20 dB. Moreover, the MXene@Ag@PA hybrid material could be used to further enhance the mechanical properties of EVA composites under electron beam irradiation. Thus, this study contributes to the development of MXene-based EVA advanced materials that are fire-safe, have high strength, and exhibit good electromagnetic shielding performance for various applications.

128

The NEutron Detector Array (NEDA) is designed to be coupled to gamma-ray spectrometers to enhance the sensitivity of the setup by enabling reaction channel selection through counting of the evaporated neutrons. This article presents the implementation of a double trigger condition system for NEDA, which improves the acquisition of neutrons and reduces the number of gamma rays acquired. Two independent triggers are generated in the double trigger condition system: one based on charge comparison (CC) and the other on time-of-flight (TOF). These triggers can be combined using OR and AND logic, offering four distinct trigger modes. The developed firmware is added to the previous one in the Virtex 6 field programmable gate array (FPGA) present in the system, which also includes signal processing, baseline correction, and various trigger logic blocks. The performance of the trigger system is evaluated using data from the E703 experiment performed at GANIL. The four trigger modes are applied to the same data and a subsequent offline analysis is performed. It is shown that most of the detected neutrons are preserved with the AND mode, and the total number of gamma rays is significantly reduced. Compared with the CC trigger mode, the OR trigger mode allows increasing the selection of neutrons. In addition, it is demonstrated that if the OR mode is selected, the online CC trigger threshold can be raised without losing neutrons.

145

Track reconstruction algorithms are critical for polarization measurements. Convolutional neural networks (CNNs) are a promising alternative to traditional moment-based track reconstruction approaches. However, the hexagonal grid track images obtained using gas pixel detectors (GPDs) for better anisotropy do not match the classical rectangle-based CNN, and converting the track images from hexagonal to square results in a loss of information.We developed a new hexagonal CNN algorithm for track reconstruction and polarization estimation in X-ray polarimeters, which was used to extract the emission angles and absorption points from photoelectron track images and predict the uncertainty of the predicted emission angles. The simulated data from the PolarLight test were used to train and test the hexagonal CNN models. For individual energies, the hexagonal CNN algorithm produced 15%–30% improvements in the modulation factor compared to the moment analysis method for 100% polarized data, and its performance was comparable to that of the rectangle-based CNN algorithm that was recently developed by the Imaging X-ray Polarimetry Explorer team, but at a lower computational and storage cost for preprocessing.

156

Pulse pile-up is a problem in nuclear spectroscopy and nuclear reaction studies that occurs when two pulses overlap and distort each other, degrading the quality of energy and timing information. Different methods have been used for pile-up rejection, both digital and analogue, but some pile-up events may contain pulses of interest and need to be reconstructed. The paper proposes a new method for reconstructing pile-up events acquired with a Neutron Detector Array (NEDA) using an one-dimensional convolutional autoencoder (1D-CAE). The datasets for training and testing the 1D-CAE are created from data acquired from the NEDA. The new pile-up signal reconstruction method is evaluated from the point of view of how similar the reconstructed signals are to the original ones. Furthermore, it is analysed considering the result of the neutron-gamma discrimination based on Charge Comparison (CC), comparing the result obtained from original and reconstructed signals.

126

The Cooling Storage Ring of the Heavy Ion Research Facility in Lanzhou (HIRFL-CSR) was constructed to study nuclear physics, atomic physics, interdisciplinary science, and related applications. The External Target Facility (ETF) is located in the main ring of the HIRFL-CSR. The gamma detector of the ETF is built to measure emitted gamma rays with energies below 5 MeV in the center-of-mass frame and is planned to measure light fragments with energies up to 300 MeV. The readout electronics for the gamma detector were designed and commissioned. The readout electronics consist of thirty-two front-end cards, thirty-two readout control units (RCUs), one common readout unit, one synchronization clock unit, and one sub-trigger unit. By using the real-time peak-detection algorithm implemented in the RCU, the data volume can be significantly reduced. In addition, trigger logic-selection algorithms are implemented to improve the selection of useful events and reduce the data size. The test results show that the integral nonlinearity of the readout electronics is less than 1%, and the energy resolution for measuring the ⁶⁰Co source is better than 5.5%. This study discusses the design and performance of the readout electronics.

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