Nuclear Science and Techniques最新文献

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 (alpha)-decay energies for 1169 nuclei with (50 le Z le 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 (alpha)-decay energies for the two new isotopes (^{204})Ac (Huang et al. Phys Lett B 834, 137484 (2022)) and (^{207})Th (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 (alpha)-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 (alpha)-decay properties.

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.

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.

One-neutron stripping process between (^{6})Li and (^{209})Bi was studied at 28, 30, and 34 MeV using the in-beam (gamma )-ray spectroscopy method. The (gamma )–(gamma ) coincident analysis clearly identified two (gamma )-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 (^6)Li+(^{209})Bi 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 (^6)Li. The calculations indicated that the first excited state of (^5)Li is critical in the actual one-neutron transfer mechanism, and the valence proton of (^{209}textrm{Bi}) can be excited to the low-lying excited state in ((^{6}textrm{Li}),(^{5}textrm{Li})) reaction, unlike in the (d,p) reaction.

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.

We investigated (^{50,52-54})Cr-induced fusion reactions for the synthesis of the superheavy element in the (104le Zle 122) range. The cross sections produced in this investigation using (^{54})Cr 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 (^{53})Cr+(^{243})Am, 23.2 fb at 236 MeV for (^{54})Cr+(^{247})Cm, 95.6 fb at 240 MeV for (^{53})Cr+(^{248})Bk, and 1.33 fb at 242 MeV for (^{53})Cr+(^{250})Cf. Consequently, these projected cross sections with excitation energy and beam energy will be useful in future Cr-induced fusion reaction investigations.

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 (sim)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 (ge)1.6.

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, beam transverse oscillation, and longitudinal oscillation. The results of the beam experiments show that under the user operation conditions of the SSRF, a beam excitation signal with an amplitude uncertainty of 2% can be reconstructed.

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.

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 is 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 1.08 × 10^–2 to 3.84 × 10^–3, 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.