Abstract：This work is an attempt to improve the Bayesian neural network (BNN) for studying photoneutron yield cross sections as a function of the charge number Z, mass number A, and incident energy ε. The BNN was improved in terms of three aspects: numerical parameters, input layer, and network structure. First, by minimizing the deviations between the predictions and data, the numerical parameters, including the hidden layer number, hidden node number, and activation function, were selected. It was found that the BNN with three hidden layers, 10 hidden nodes, and sigmoid activation function provided the smallest deviations. Second, based on known knowledge, such as the isospin dependence and shape effect, the optimal ground-state properties were selected as input neurons. Third, the Lorentzian function was applied to map the hidden nodes to the output cross sections, and the empirical formula of the Lorentzian parameters was applied to link some of the input nodes to the output cross sections. It was found that the last two aspects improved the predictions and avoided overfitting, especially for the axially deformed nucleus.
Abstract：Research performed during the past decade revealed an important role of symmetry energy in the equation of state (EOS) of strange quark matter (SQM). By introducing an isospin-dependent term into the quark mass scaling, the SQM stability window in the equivparticle model was studied. The results show that a sufficiently strong isospin dependence CI can significantly widen the SQM region of absolute stability, yielding results that simultaneously satisfy the constraints of the astrophysical observations of PSR J1614-2230 with 1.928 ± 0.017 M⊙ and tidal deformability 70 ≤ Λ1.4 ≤ 580 measured in the event GW170817. With increasing CI, the difference between the u, d, and s quark fractions for the SQM in β-equilibrium becomes inconspicuous for C>0, leading to small isospin asymmetry δ, and further resulting in similar EOS and structures of strange quark stars (SQSs). Moreover, unlike the behavior of the maximum mass of u–d QSs, which varies with CI depending on the sign of the parameter C, the maximum mass of the SQSs decreases monotonously with increasing CI.
Abstract：The penalized least squares (PLS) method with appropriate weights has proven to be a successful baseline estimation method for various spectral analyses. It can extract the baseline from the spectrum while retaining the signal peaks in the presence of random noise. The algorithm is implemented by iterating over the weights of the data points. In this study, we propose a new approach for assigning weights based on the Bayesian rule. The proposed method provides a self-consistent weighting formula and performs well, particularly for baselines with different curvature components. This method was applied to analyze Schottky spectra obtained in 86Kr projectile fragmentation measurements in the experimental Cooler Storage Ring (CSRe) at Lanzhou. It provides an accurate and reliable storage lifetime with a smaller error bar than existing PLS methods. It is also a universal baseline-subtraction algorithm that can be used for spectrum-related experiments, such as precision nuclear mass and lifetime measurements in storage rings.
Keywords：Penalized least squares;Baseline correction;Bayesian rule;Spectrum analysis
Abstract：The effects of annealing and irradiation on the evolution of Cu clusters in α-Fe are investigated using object kinetic Monte Carlo simulations. In our model, vacancies act as carriers for chemical species via thermally activated diffusion jumps, thus playing an important role in solute diffusion. At the end of the Cu cluster evolution, the simulations of the average radius and number density of the clusters are consistent with the experimental data, which indicates that the proposed simulation model is applicable and effective. For the simulation of the annealing process, it is found that the evolution of the cluster size roughly follows the 1/2 time power law with the increase in radius during the growth phase and the 1/3 time power law during the coarsening phase. In addition, the main difference between neutron and ion irradiation is the growth and evolution process of the copper-vacancy clusters. The aggregation of vacancy clusters under ion irradiation suppresses the migration and coarsening of the clusters, which ultimately leads to a smaller average radius of the copper clusters. Our proposed simulation model can supplement experimental analyses and provide a detailed evolution mechanism of vacancy-enhanced precipitation, thereby providing a foundation for other elemental precipitation research.
Keywords：Object kinetic Monte Carlo;Irradiation effect;Solute segregation;Reactor pressure vessel
Abstract：With the two flavor Nambu–Jona–Lasinio (NJL) model, we carried out a phenomenological study on the chiral phase structure, mesonic properties, and transport properties of momentum-space anisotropic quark matter. To calculate the transport coefficients we utilized the kinetic theory in the relaxation time approximation, where the momentum anisotropy is embedded in the estimation of both the distribution function and relaxation time. It was shown that an increase in the anisotropy parameter ξ may result in a catalysis of chiral symmetry breaking. The critical endpoint (CEP) is shifted to lower temperatures and larger quark chemical potentials as ξ increases, and the impact of momentum anisotropy on the CEP temperature is almost the same as that on the quark chemical potential of the CEP. The meson masses and the associated decay widths also exhibit a significant ξ dependence. It was observed that the temperature behavior of the scaled shear viscosity η/T3 and scaled electrical conductivity σel/T exhibited a similar dip structure, with the minima of both η/T3 and σel/T shifting toward higher temperatures with increasing ξ. Furthermore, we demonstrated that the Seebeck coefficient S decreases when the temperature rises and its sign is positive, indicating that the dominant carriers for converting the temperature gradient to the electric field are up-quarks. The Seebeck coefficient S is significantly enhanced with a large ξ for a temperature below the critical temperature.
Abstract：The single-event effect (SEE) is a serious threat to electronics in radiation environments. The most important issue in radiation-hardening studies is the localization of the sensitive region in electronics to the SEE. To solve this problem, a prototype based on a complementary metal oxide semiconductor (CMOS) pixel sensor, i.e., Topmetal-M, was designed for SEE localization. A beam test was performed on the prototype at the radiation terminal of the Heavy Ion Research Facility in Lanzhou (HIRFL). The results indicated that the inherent deflection angle of the prototype to the beam was 1.7, and the angular resolution was 0.6. The prototype localized heavy ions with a position resolution of 3.4 μm.
Abstract：Detector and event visualization are essential parts of the software used in high-energy physics (HEP) experiments. Modern visualization techniques and multimedia production platforms such as Unity provide impressive display effects and professional extensions for visualization in HEP experiments. In this study, a method for automatic detector description transformation is presented, which can convert the complicated HEP detector geometry from GDML in offline software to 3D modeling in Unity. The method was successfully applied in the BESIII experiment and can be further developed into applications such as event displays, data monitoring, or virtual reality. It has great potential in detector design, offline software development, physics analysis, and outreach for next-generation HEP experiments as well as applications in nuclear techniques for the industry.
Abstract：Core axial power distribution is an essential topic in pressurized water reactor (PWR) reactivity control. Traditional PWRs limit stability against axial core power oscillations at a high-cycle burnup. Because the "camel" peak power shape typically occurs with increasing depletion, the approaches used for the axial power control deserve special attention. This study aims to investigate the performance of different gadolinium rod design schemes in core axial power control during power operation based on the reactivity balance strategy, and to propose new multi-concentration gadolinium rod design schemes. In the new design schemes, low-concentration gadolinium pellets are filled in the axial hump part of the gadolinium rod, and high-concentration gadolinium pellets are filled in the other parts. The impact of different gadolinium rod design schemes on the main core characteristics was evaluated using the nuclear design code package PCM developed by CGN. The results show that the new gadolinium rod design significantly impacts the core axial power shape. The new design schemes can efficiently improve the core axial power distribution along the entire cycle by reducing the core axial power peak at the end of a cycle, enhancing the reactor operation stability, and achieving a better core safety margin, revealing a sizeable potential application.
Keywords：Gadolinium;PCM software package;Fuel assembly;Core axial power distribution;Reactivity
Abstract：Real-time monitoring of the 14-MeV D-T fusion neutron yield is urgently required for the triton burnup study on the Experimental Advanced Superconducting Tokamak (EAST). In this study, we developed an optimal design of a fast-neutron detector based on the scintillating fiber (Sci-Fi) to provide D-T neutron yield through Geant4 simulation. The effect on the detection performance is concerned when changing the number of the Sci-Fis embedded in the probe head, minimum distance between the fibers, length of the fibers, or substrate material of the probe head. The maximum number of scintillation photons generated by the n/γ source particles and output by the light guide within an event (event: the entire simulation process for one source particle) was used to quantify the n/γ resolution of the detector as the main basis. And the intrinsic detection efficiency was used as another evaluation criterion. The results demonstrate that the optimal design scheme is to use a 5-cm probe head whose substrate material is pure aluminum, in which 463 Sci-Fis with the same length of 5 cm are embedded, and the minimum distance between the centers of the two fibers is 2 mm. The optimized detector exhibits clear directionality in the simulation, which is in line with the expectation and experimental data provided in the literature. This study presents the variation trends of the performance of the Sci-Fi detector when its main parameters change, which is beneficial for the targeted design and optimization of the Sci-Fi detector used in a specific radiation environment.
Abstract：Betavoltaic cells (BCs) are promising self-generating power cells with long life and high power density. However, the low energy conversion efficiency (ECE) has limitations in practical engineering applications. Wide-bandgap semiconductors (WBGSs) with three-dimensional (3-D) nanostructures are ideal candidates for increasing the ECE of BCs. This paper proposes hydrothermally-grown ZnO nanorod arrays (ZNRAs) for 63Ni-powered BCs. A quantitative model was established for simulation using the parameter values of the dark characteristics, which were obtained from the experimental measurements for a simulated BC based on a Ni-incorporated ZNRAs structure. Monte Carlo (MC) modeling and simulation were conducted to obtain the values of the β energy deposited in ZNRAs with different nanorod spacings and heights. Through the simulation and optimization of the 3-D ZNRAs and 2-D ZnO bulk structures, the performance of the 63Ni-powered BCs based on both structures was evaluated using a quantitative model. The BCs based on the 3-D ZNRAs structure and 2-D ZnO bulk structure achieved a maximum ECE of 10.1% and 4.69%, respectively, which indicates the significant superiority of 3-D nanostructured WBGSs in terms of increasing the ECE of BCs.
Keywords：Betavoltaic cells;Monte Carlo simulation;ZnO nanorod arrays;Quantitative model;Performance evaluation.
Abstract：To perform nuclear reactor simulations in a more realistic manner, the coupling scheme between neutronics and thermal-hydraulics was implemented in the HNET program for both steady-state and transient conditions. For simplicity, efficiency, and robustness, the matrix-free Newton/Krylov (MFNK) method was applied to the steady-state coupling calculation. In addition, the optimal perturbation size was adopted to further improve the convergence behavior of the MFNK. For the transient coupling simulation, the operator splitting method with a staggered time mesh was utilized to balance the computational cost and accuracy. Finally, VERA Problem 6 with power and boron perturbation and the NEACRP transient benchmark were simulated for analysis. The numerical results show that the MFNK method can outperform Picard iteration in terms of both efficiency and robustness for a wide range of problems. Furthermore, the reasonable agreement between the simulation results and the reference results for the NEACRP transient benchmark verifies the capability of predicting the behavior of the nuclear reactor.
Abstract：In the Chinese ADS front-end demo superconducting radiofrequency linac (CAFe) at the Institute of Modern Physics, a burst-noise signal-triggered cavity fault frequently appears during beam commissioning. These events are characterized by a rapid burst noise in the cavity pick-up, which may lead to an unexpected low-level radiofrequency (LLRF) response that eventually causes a cavity fault. To eliminate the undesirable reaction of the LLRF control loop, we propose a method that uses a burst-noise detection and processing algorithm integrated into the LLRF feedback controller. This algorithm can prevent undesired regulations in LLRF systems. Data analysis revealed that some burst-noise events did not exhibit measurable energy loss. In contrast, the other events were accompanied by a rapid loss of cavity stored energy and exhibited similarities to the "E-quench" phenomena reported in other laboratories. A particle-in-cell simulation indicated that the suspected E-quench phenomenon may be related to a plasma formation process inside the cavity. Fortunately, the LLRF algorithm is robust to the two different types of burst-noise events and can significantly mitigate the corresponding cavity faults in CAFe beam commissioning.
Abstract：A miniaturized neutron spin flipper based on a high-TC superconductor film, developed at the China Spallation Neutron Source (CSNS), is presented. A neutron spin flipper is an essential component for performing polarized neutron experiments and, as such, constitutes a high priority for developing CSNS’s polarized neutron capability. To provide the beamlines with a universal neutron spin flipper operating over a wide wavelength band, the neutron spin flipper utilizes non-adiabatic spin flipping during transit through opposite magnetic fields that are mutually shielded by the superconductor Meissner effect. A compact vacuum heat shield and a low-power consumption sterling refrigerator maintained the superconducting condition while reducing the size and power input of the flipper. The prototype device was tested at the CSNS BL-20, which demonstrated a flipping efficiency of 99 % at 4 Å.
Abstract：To implement the Tsinghua Thomson Scattering X-ray Source (TTX) upgrade plan and the Very Compact Inverse Compton Scattering Gamma-ray Source (VIGAS) program, a new 1.5-m traveling-wave accelerating structure was designed to replace the old 3-m SLAC-type structure with the aim of increasing the accelerating gradient from 15 to 30 MV/m. The new type of structure works in the 3π/4 mode with a comparatively low group velocity varying from 0.007c to 0.003c to increase the accelerating gradient at a given power. An elliptical iris was employed to reduce the surface field enhancement. The filling process of the low-group-velocity structure was analyzed using a circuit model. After fabrication, the structure was precisely tuned using the non-contact tuning method, followed by detailed low-power radiofrequency measurements. The structure was first installed and utilized at a beamline for the Terahertz experiment at Tsinghua University. After 120 h of conditioning, it is now operating at a gradient of 24.2 MV/m and a 20.7-MW input power, with the klystron operating at its full power. It is expected to generate an accelerating gradient of 30 MV/m when the klystron power is upgraded to 30 MW in the near future.
Keywords：Traveling-wave accelerating structure;Cavity optimization;Tuning method;High-power test
Abstract：At the High Energy Photon Source (HEPS), a high orbital stability of typically 10 % of the beam size and angular divergence must be achieved. The beam size at the insertion devices is 10 μm horizontally and 1 μm vertically, which implies that the beam orbit must be stabilized to the sub-micrometer level. This results in stringent tolerance and quality control requirements for the series production of beam position monitor (BPM) pickups. In this study, analytical formulas were used and CST simulations were performed to analyze the effects of the mechanical tolerances of BPM pickups on beam position measurement. The results of electromagnetic field simulations revealed how various mechanical errors, such as button size and location accuracy, as well as the related button capacitance, exert different influences on the beam position measurement. The performance of an actual BPM pickup was measured, along with an assessment of the error on the beam position measurement. Additionally, a wakefield analysis, including an investigation of trapped resonant modes and related thermal deformation, was conducted.
Keywords：High Energy Photon Source;BPM;Error;CST;Tolerances