Nuclear Science and Techniques最新文献

Understanding the properties of nuclei near the double magic nucleus ⁴⁰Ca is crucial for both nuclear theory and experiments. In this study, Ca isotopes were investigated using an extended pairing-plus-quadrupole model with monopole corrections. The negative-parity states of ⁴⁴Ca were coupled with the intruder orbital (g_{9/2}) at 4 MeV. The values of (E_{4+})/(E_{2+}) agree well with experimental trend from ⁴²Ca to ⁵⁰Ca, considering monopole effects between (nu f_{7/2}) and (nu p_{3/2})((nu f_{5/2})). This monopole effect, determined from data of ⁴⁸Ca and ⁵⁰Ca, supports the proposed new nuclear magic number (N = 34) by predicting a high-energy (2^{+}) state in ⁵⁴Ca.

The back-streaming white-neutron beamline (Back-n) of the China Spallation Neutron Source is an essential neutron-research platform built for the study of nuclear data, neutron physics, and neutron applications. Many types of cross-sectional neutron-reaction measurements have been performed at Back-n since early 2018. These measurements have shown that a significant number of gamma rays can be transmitted to the experimental stations of Back-n along with the neutron beam. These gamma rays, commonly referred to as in-beam gamma rays, can induce a non-negligible experimental background in neutron-reaction measurements. Studying the characteristics of in-beam gamma rays is important for understanding the experimental background. However, measuring in-beam gamma rays is challenging because most gamma-ray detectors are sensitive to neutrons; thus, discriminating between neutron-induced signals and those from in-beam gamma rays is difficult. In this study, we propose the use of the black resonance filter method and a (hbox {CeBr}_{3}) scintillation detector to measure the characteristics of the in-beam gamma rays of Back-n. Four types of black resonance filters, ¹⁸¹Ta, ⁵⁹Co, ^natAg, and ^natCd, were used in this measurement. The time-of-flight (TOF) technique was used to select the detector signals remaining in the absorption region of the TOF spectra, which were mainly induced by in-beam gamma rays. The energy distribution and flux of the in-beam gamma rays of Back-n were determined by analyzing the deposited energy spectra of the (hbox {CeBr}_{3}) scintillation detector and using Monte Carlo simulations. Based on the results of this study, the background contributions from in-beam gamma rays in neutron-reaction measurements at Back-n can be reasonably evaluated, which is beneficial for enhancing both the experimental methodology and data analysis.

We investigated the properties of the phase diagram of high-order susceptibilities, speed of sound, and polytropic index based on an extended Nambu-Jona-Lasinio model with an eight-quark scalar-vector interaction. Non-monotonic behavior was observed in all these quantities around the phase transition boundary, which also revealed the properties of the critical point. Further, this study indicated that the chiral phase transition boundary and critical point could vary depending on the scalar-vector coupling constant (G_text {SV}). At finite densities and temperatures, the negative (G_text {SV}) term exhibited attractive interactions, which enhanced the critical point temperature and reduced the chemical potential. The (G_text {SV}) term also affected the properties of the high-order susceptibilities, speed of sound, and polytropic index near the critical point. The non-monotonic (peak or dip) structures of these quantities shifted to a low baryon chemical potential (and high temperature) with a negative (G_text {SV}). (G_text {SV}) also changed the amplitude and range of the nonmonotonic regions. Therefore, the scalar-vector interaction was useful for locating the phase boundary and critical point in QCD phase diagram by comparing the experimental data. The study of the non-monotonic behavior of high-order susceptibilities, speed of sound, and polytropic index is of great interest, and further observations related to high-order susceptibilities, speed of sound, and polytropic index being found and applied to the search for critical points in heavy-ion collisions and the study of compact stars are eagerly awaited.

The round-beam operation presents many benefits for scientific experiments regarding synchrotron radiation and the weakening influences of intra-beam scattering in diffraction-limited synchrotron light sources. A round-beam generation method based on the global setting of skew quadrupoles and the application of a non-dominated sorting genetic algorithm was proposed in this study. Two schemes, including large-emittance coupling introduced via betatron coupling and vertical dispersion, were explored in a candidate lattice for an upgrade-proposal of the Shanghai synchrotron radiation facility. Emittance variations with lattice imperfections and their influence on the beam dynamics of beam optic distortions were investigated. The results demonstrated that a precise coupling control ranging from 10 to 100% was achieved under low optical distortion, whereas full-coupling generation and its robustness were achieved by our proposed method by adjusting the skew quadrupole components located in the dispersion-free sections. The Touschek lifetime increased by a factor of 2–2.5.

Based on the dinuclear system model, the synthesis of the predicted double-magic nuclei ({^{298}hbox {Fl}}) and ({^{304}hbox {120}}) was investigated via neutron-rich radioactive beam-induced fusion reactions. The reaction ({^{58}hbox {Ca}}+{^{244}hbox {Pu}}) is predicted to be favorable for producing ({^{298}hbox {Fl}}) with a maximal ER cross section of ({0.301},hbox {pb}). Investigations of the entrance channel effect reveal that the ({^{244}hbox {Pu}}) target is more promising for synthesizing ({^{298}hbox {Fl}}) than the neutron-rich targets ({^{248}hbox {Cm}}) and ({^{249}hbox {Bk}}), because of the influence of the Coulomb barrier. For the synthesis of ({^{304}hbox {120}}), the maximal ER cross section of ({0.046},hbox {fb}) emerges in the reaction ({^{58}hbox {V}}+{^{249}hbox {Bk}}), indicating the need for further advancements in both experimental facilities and reaction mechanisms.

A passive neutron multiplicity measurement device, FH-NCM/S1, based on field-programmable gate arrays (FPGAs), is developed specifically for measuring the mass of plutonium-240 (²⁴⁰Pu) in mixed oxide fuel. FH-NCM/S1 adopts an integrated approach, combining the shift register analysis mode with the pulse-position timestamp mode using an FPGA. The optimal effective length of the ³He neutron detector was determined to be 30 cm, and the thickness of the graphite reflector was ascertained to be 15 cm through MCNP simulations. After fabricating the device, calibration measurements were performed using a ²⁵²Cf neutron source; a detection efficiency of 43.07% and detector die-away time of 55.79 ({upmu })s were observed. Nine samples of plutonium oxide were measured under identical conditions using the FH-NCM/S1 in shift register analysis mode and a plutonium waste multiplicity counter. The obtained double rates underwent corrections for detection efficiency ((varepsilon)) and double gate fraction ((f_{rm d})), resulting in corrected double rates ((D_{rm c})), which were used to validate the accuracy of the shift register analysis mode. Furthermore, the device exhibited fluctuations in the measurement results, and within a single 20 s measurement, these fluctuations remained below 10%. After 30 cycles, the relative error in the mass of ²⁴⁰Pu was less than 5%. Finally, correlation calculations confirmed the robust consistency of both measurement modes. This study holds specific significance for the subsequent design and development of neutron multiplicity devices.

To further research on high-parameter plasma, we plan to develop a two-dimensional hard X-ray (HXR) imaging system at the HL-3 tokamak to measure HXRs with energies ranging from 20 to 300 keV. The application of an array-structured detector ensures that this system can measure HXR-radiation spectra from the entire plasma cross section. Therefore, it is suitable for the study of fast-electron physics, such as radio-frequency wave current drives, fast electrons driving instabilities, and plasma disruptions in fusion research. In this study, we develop a simulation for calculating fast-electron bremsstrahlung in the HL-3 tokamak based on the Monte Carlo simulation code Geant4, in which the plasma geometry and forward scattering of fast-electron bremsstrahlung are considered. The preliminary calculation results indicate that the HXR energy deposition on the detector is symmetrically distributed, even though the plasma distribution is asymmetric owing to the toroidal effect. These simulation results are helpful in constructing the relationship between the energy deposition on the detector and parameter distribution on the plasma cross section during HL-3 experiments. This is beneficial for the reconstruction of the fast-electron-distribution function and for optimizing the design of the HXR-imaging system.

The high-intensity heavy-ion accelerator facility (HIAF) is a scientific research facility complex composed of multiple cascade accelerators of different types, which pose a scheduling problem for devices distributed over a certain range of 2 km, involving over a hundred devices. The white rabbit, a technology-enhancing Gigabit Ethernet, has shown the capability of scheduling distributed timing devices but still faces the challenge of obtaining real-time synchronization calibration parameters with high precision. This study presents a calibration system based on a time-to-digital converter implemented on an ARM-based System-on-Chip (SoC). The system consists of four multi-sample delay lines, a bubble-proof encoder, an edge controller for managing data from different channels, and a highly effective calibration module that benefits from the SoC architecture. The performance was evaluated with an average RMS precision of 5.51 ps by measuring the time intervals from 0 to 24,000 ps with 120,000 data for every test. The design presented in this study refines the calibration precision of the HIAF timing system. This eliminates the errors caused by manual calibration without efficiency loss and provides data support for fault diagnosis. It can also be easily tailored or ported to other devices for specific applications and provides more space for developing timing systems for particle accelerators, such as white rabbits on HIAF.

A sustainability-oriented assessment of the nuclear energy system can provide informative and convincing decision-making support for nuclear development strategies in China. In our previous study, four authentic nuclear fuel cycle (NFC) transition scenarios were proposed, featuring different development stages and exhibiting distinct environmental, economic, and technical characteristics. However, because of the multiple and often conflicting criteria embedded therein, determining the top-priority NFC alternative for a sustainability orientation remains challenging. To address this issue, this study proposed a novel hybrid multi-criteria decision-making framework comprising fuzzy AHP, PROMETHEE GAIA, and MOORA. Initially, an improved fuzzy AHP weighting model was developed to determine criteria weights under uncertainty and investigate the influence of various weight aggregation and defuzzification approaches. Subsequently, PROMETHEE GAIA was used to address conflicts among the criteria and prioritize alternatives on a visualized k-dimensional GAIA plane. As a result, the alternative for direct recycling PWR spent fuel in fast reactors is considered the most sustainable. Furthermore, a sensitivity analysis was conducted to examine the influence of criteria weight variation and validate the screening results. Finally, using MOORA, some significant optimization ideas and valuable insights were provided to support decision-makers in shaping nuclear development strategies.

A Johann-type X-ray spectrometer was successfully developed at the hard X-ray branch (in-vacuum undulator with a 24-mm periodic length) of the energy material beamline (E-line) at the Shanghai Synchrotron Radiation Facility (SSRF). This spectrometer was utilized to implement X-ray emission spectroscopy (XES), high-energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS), and resonant inelastic X-ray scattering. Seven spherically bent crystals were positioned on the respective vertical 500-mm-diameter Rowland circles, adopting an area detector to increase the solid angle to 1.75(%) of 4 (pi) sr, facilitating the study of low-concentrate systems under complex reaction conditions. Operated under the atmosphere pressure, the spectrometer covers the energy region from 3.5 to 18 keV, with the Bragg angle ranging from 73(^{circ }) to 86(^{circ }) during vertical scanning. It offers a promised energy resolution of sub-eV (XES) and super-eV (HERFD-XAS). Generally, these comprehensive core-level spectroscopy methods based on hard X-rays at the E-line with an extremely high photon flux can meet the crucial requirements of a green energy strategy. Moreover, they provide substantial support for scientific advances in fundamental research.