Vol.32,

The fusion dynamics of the formation of superheavy nuclei were investigated thoroughly within the dinuclear system model. The Monte Carlo approach was implemented in the nucleon transfer process to include all possible orientations, at which the dinuclear system is assumed to be formed at the touching configuration of dinuclear fragments. The production cross sections of superheavy nuclei Cn, Fl, Lv, Ts, and Og were calculated and compared with the available data from Dubna. The evaporation residue excitation functions in the channels of pure neutrons and charged particles were systematically analyzed. The combinations of ⁴⁴Sc, ^48,50Ti, ^49,51V, ^52,54Cr, ^58,62Fe, and ^62,64Ni bombarding the actinide nuclides ²³⁸U, ²⁴⁴Pu, ²⁴⁸Cm, ^247,249Bk, ^249,251Cf, ²⁵²Es, and ²⁴³Am were calculated to produce the superheavy elements with Z=119-122. We obtained that the production cross sections sensitively depend on the neutron richness of the reaction system. The structure of the evaporation residue excitation function is related to the neutron separation energy and fission barrier of the compound nucleus.

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The mid-rapidity transverse momentum spectra of charmed mesons in Pb-Pb and pp(p¯) collisions are analyzed using the Tsallis–Pareto distribution derived from non-extensive statistics. We provide uniform descriptions of both small and large systems over a wide range of collision energies and hadron transverse momenta. By establishing the relationship between the event multiplicity and Tsallis parameters, we observe that there is a significant linear relationship between the thermal temperature and Tsallis q parameter in Pb-Pb collisions at sNN = 2.76 TeV and 5.02 TeV. Further, the slope of the T–(q-1) parameter plot is positively correlated with the hadron mass. In addition, charmed mesons have a higher thermal temperature than light hadrons at the same q-1, indicating that the charm flavor requires a higher temperature to reach the same degree of non-extensivity as light flavors in heavy-ion collisions. The same fit is applied to the transverse momentum spectra of charmed mesons in pp(p¯) collisions over a large energy range using the Tsallis–Pareto distribution. It is found that the thermal temperature increases with system energy, whereas the q parameter becomes saturated at the pp(p¯) limit, q-1 = 0.142 ± 0.010. In addition, the results of most peripheral Pb-Pb collisions are found to approach the pp(p¯) limit, which suggests that more peripheral heavy-ion collisions are less affected by the medium and more similar to pp(p¯) collisions.

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Background: The masses of ~2500 nuclei have been measured experimentally; however, >7000 isotopes are predicted to exist in the nuclear landscape from H (Z=1) to Og (Z=118) based on various theoretical calculations. Exploring the mass of the remaining isotopes is a popular topic in nuclear physics. Machine learning has served as a powerful tool for learning complex representations of big data in many fields. Purpose: We use Light Gradient Boosting Machine (LightGBM), which is a highly efficient machine learning algorithm, to predict the masses of unknown nuclei and to explore the nuclear landscape on the neutron-rich side from learning the measured nuclear masses. Methods: Several characteristic quantities (e.g., mass number and proton number) are fed into the LightGBM algorithm to mimic the patterns of the residual δ(Z,A) between the experimental binding energy and the theoretical one given by the liquid-drop model (LDM), Duflo–Zucker (DZ, also dubbed DZ28) mass model, finite-range droplet model (FRDM, also dubbed FRDM2012), as well as the Weizsäcker–Skyrme (WS4) model to refine these mass models. Results: By using the experimental data of 80% of known nuclei as the training dataset, the root mean square deviations (RMSDs) between the predicted and the experimental binding energy of the remaining 20% are approximately 0.234± 0.022, 0.213± 0.018, 0.170± 0.011, and 0.222± 0.016 MeV for the LightGBM-refined LDM, DZ model, WS4 model, and FRDM, respectively. These values are approximately 90%, 65%, 40%, and 60% smaller than those of the corresponding origin mass models. The RMSD for 66 newly measured nuclei that appeared in AME2020 was also significantly improved. The one-neutron and two-neutron separation energies predicted by these refined models are consistent with several theoretical predictions based on various physical models. In addition, the two-neutron separation energies of several newly measured nuclei (e.g., some isotopes of Ca, Ti, Pm, and Sm) predicted with LightGBM-refined mass models are also in good agreement with the latest experimental data. Conclusions: LightGBM can be used to refine theoretical nuclear mass models and predict the binding energy of unknown nuclei. Moreover, the correlation between the input characteristic quantities and the output can be interpreted by SHapley additive exPlanations (a popular explainable artificial intelligence tool), which may provide new insights for developing theoretical nuclear mass models.

604

The bulk viscosity of interacting strange quark matter in a strong external magnetic field B_m with a real equation of state is investigated. It is found that interquark interactions can significantly increase the bulk viscosity, and the magnetic field B_m can cause irregular oscillations in both components of the bulk viscosity, ζ∥ (parallel to B_m) and ζ⊥ (perpendicular to B_m). A comparison with non-interacting strange quark matter reveals that when B_m is sufficiently large, ζ⊥ is more affected by interactions than ζ∥. Additionally, the quasi-oscillation of the bulk viscosity with changes in density may facilitate the formation of magnetic domains. Moreover, the resulting r-mode instability windows are in good agreement with observational data for compact stars in low-mass X-ray binaries. Specifically, the r-mode instability window for interacting strange quark matter in high magnetic fields has a minimum rotation frequency exceeding 1050 Hz, which may explain the observed very high spin frequency of a pulsar with ν=1122 Hz.

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A multi-phase transport (AMPT) model was constructed as a self-contained kinetic theory-based description of relativistic nuclear collisions as it contains four main components: the fluctuating initial condition, a parton cascade, hadronization, and a hadron cascade. Here we review the main developments after the first public release of the AMPT source code in 2004 and the corresponding publication that described the physics details of the model at that time. We also discuss possible directions for future developments of the AMPT model to better study the properties of the dense matter created in relativistic collisions of small or large systems.

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A suitable model for high-temperature heat pipe startup is a prerequisite to realizing the numerical simulation for the heat pipe cooled reactor startup from the cold state. It is required that this model not only describe the transient behavior during the startup period, but also reduce the computing resources of the heat pipe cooled reactor simulation in the simplest way. In this study, a simplified model that integrates the two-zone and network models is proposed. In this model, vapor flow in the vapor space, evaporation, and condensation in the vapor-liquid interface are decoupled with heat conduction to achieve a fast calculation of the transient characteristics of the heat pipe. An experimental system for a high-temperature heat pipe was developed to validate the proposed model. A potassium heat pipe was utilized as the experimental material. Startup experiments were performed with different heating powers. Compared with the experimental results, the accuracy of the proposed model was verified. Moreover, the proposed model can predict the vapor flow, pressure drop, and temperature drop in the vapor space. As indicated by the analysis results, the essential requirements for successful startup are also determined. The heat pipe cannot achieve a successful startup until the heating power satisfies these requirements. All the discussions indicate the capability of the proposed model for the simulation of a high-temperature heat pipe startup from the frozen state; hence, can act as a basic tool for the heat pipe cooled reactor simulation.

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The propagation of single-event effects (SEEs) on a Xilinx Zynq-7000 system on a chip (SoC) was investigated using heavy-ion microbeam radiation. The irradiation results reveal several functional blocks' sensitivity locations and cross sections, for instance, the arithmetic logic unit, register, D-cache, and peripheral, while irradiating the on-chip memory (OCM) region. Moreover, event tree analysis was executed based on the obtained microbeam irradiation results. This study quantitatively assesses the probabilities of SEE propagation from the OCM to other blocks in the SoC.

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High-level waste is an important safety issue in the development of nuclear power. A proposed solution is the transmutation of waste in fast reactors. The exclusion of the risk of supercriticality by using subcritical reactors is currently under development. Controlling the subcriticality level in such reactors presents difficulties. A problem is posed by the so-called space effect observed when using in reactors many neutron detectors in different locations of the core and reflector. Reactivity obtained from measurements, for example, by the Sjöstrand method, differs by nonnegligible values. Numerical corrections can partially improve this situation. The use of a monoisotopic fission chamber set, designed for a given reactor, when each chamber is intended for a specific position in the system, can improve the situation. A question arises about the sensitivity of the results to reactivity changes. This issue is analyzed by computer simulation for possible fissionable and fissile nuclides for the total range of control rod insertion, changes in reactor fuel enrichment, and fuel temperature. The tested sensitivity was satisfactory at most levels from several dozen to several hundred pcm. A case study was conducted using the VENUS-F core model.

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The 10-MeV Accelerator-Driven Subcritical (ADS) system injector-I test stand at the Institute of High Energy Physics (IHEP) is a testing facility dedicated to demonstrating the feasibility of the spoke-based super conducting (SC) linear accelerator (linac) for the ADS project in China. The injector adopted a four-vane copper structure radio frequency quadrupole (RFQ) with an output energy of 3.2 MeV and an SC section accommodating 14 β_g=0.12 single spoke cavities, 14 SC solenoids, and 14 cold beam position monitors (BPMs). A 10-MeV pulsed beam with a beam current of 10 mA and a 2-mA continuous wave (CW) beam were successfully shoting through. The commissioning results confirmed the feasibility of using a 325-MHz spoke-type cavity for accelerating the proton beam in the low β and medium β sections. This paper describes the results achieved, the difficulties encountered, and the experiences obtained during commissioning.

886

In this study, the theory of minimum detectable activity concentration (MDAC) for airborne gamma-ray spectrometry (AGS) was derived, and the relationship between the MDAC and the intrinsic efficiency of a scintillation counter, volume and energy resolution of scintillation crystals, and flight altitude of an aircraft was investigated. To verify this theory, experimental devices based on NaI and CeBr₃ scintillation counters were prepared, and the potassium, uranium, and thorium contents in calibration pads obtained via the stripping ratio method and theory were compared. The MDACs of AGS under different conditions were calculated and analyzed using the proposed theory and the Monte Carlo method. The relative errors found via a comparison of the experimental and theoretical results were less than 4%. The theory of MDAC can guide the work of AGS in probing areas with low radioactivity.

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A collector with high perveance, efficient recuperation, and low secondary emissions is required for the 450-keV electron cooler in the HIAF accelerator complex. To optimize the collection efficiency of the collector, a simulation program, based on the Monte Carlo simulations, was developed in the world’s first attempt to calculate the electron collection efficiency. In this program, the backscattering electrons and secondary electrons generated on the collector surface are calculated using a Monte Carlo approach, and all electron trajectories in the collector region are tracked by the Runge-Kutta method. In this paper, the features and structure of our program are described. The backscattering electron yields, with various collector-surface materials, are calculated using our program. Moreover, the collector efficiencies for various collector structures and electromagnetic fields are simulated and optimized. The measurement results of the collection efficiency of the HIAF collector prototype and the CSRm synchrotron are also reported. These experimental results were in good agreement with the simulation results of our program.

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To establish a nuclear resonant scattering beamline at the High Energy Photon Source (HEPS), it is essential to develop tools for detection and cleaning of parasitic bunches, for meeting the stringent demands on bunch purity. To this end, a novel time-correlated single-photon counting system was implemented at the electron storage ring of the Beijing Electron-Positron Collider II (BEPCII). The purity deterioration process over a week-long operation was recorded by the system. In this study, the mechanism of impurity growth was analyzed by numerical methods and validated on measurements. The agreement between the experimental results and the calculation was fairly good. Two main sources of parasitic bunches, pre-accelerators and the Touschek scattering, were confirmed. A bunch-cleaning technique, based on a sinusoidal signal mixed with a pseudo-square wave, was also developed and implemented, and its capability to improve the bunch purity to the level of 10^-7 was experimentally demonstrated. We present the experimental setup, principle, and measurement results of a system for detection and cleaning of parasitic bunches.

650

Most detectors for nuclear physics experiments are detector arrays composed of numerous units. Testing each detector unit is a major part of the research work on detector arrays. To save time and simplify the research process, a ROOT-based detector test system was designed for detector unit testing. The test system is a general purpose and expandable software system that can support most of the hardware devices in the market. Users can easily build a complete detector test system using the required hardware devices. The software is based on the ROOT framework and is operated on the Linux platform. The software of the test system consists of four parts: the controller, data acquisition(DAQ), high-voltage power supply, and online monitoring and analysis. In addition, a user-friendly graphical user interface (GUI) was designed for user convenience. Moreover, the online analysis function of the software can implement automatic peak searching and spectrum fitting for different radioactive sources, and the results under different conditions can be shown automatically. The completion of the test system could greatly simplify the development process of the detector.

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