Nuclear Science and Techniques最新文献

In recent years, the gap between the supply and demand of medical radioisotopes has increased, necessitating new methods for producing medical radioisotopes. Photonuclear reactions based on gamma sources have unique advantages in terms of producing high specific activity and innovative medical radioisotopes. However, the lack of experimental data on reaction cross sections for photonuclear reactions of medical radioisotopes of interest has severely limited the development and production of photonuclear transmutation medical radioisotopes. In this study, the entire process of the generation, decay, and measurement of medical radioisotopes was simulated using online gamma activation and offline gamma measurements combined with a shielding gamma-ray spectrometer. Based on a quasi-monochromatic gamma beam from the Shanghai Laser Electron Gamma Source (SLEGS), the feasibility of this measurement of production cross section for surveyed medical radioisotopes was simulated, and specific solutions for measuring medical radioisotopes with ultra-low production cross sections were provided. The feasibility of this method for high-precision measurements of the reaction cross section of medical radioisotopes was demonstrated.

In this study, we revisit the previous mass relations of mirror nuclei by considering 1/N- and 1/Z-dependent terms and the shell effect across a shell. The root-mean-squared deviation is 66 keV for 116 nuclei with neutron number (N ge 10), as compared with experimental data compiled in the AME2020 database. The predicted mass excesses of 173 proton-rich nuclei, including 98 unknown nuclei, are tabulated in the Supplemental Material herein with competitive accuracy.

As a complement to X-ray computed tomography (CT), neutron tomography has been extensively used in nuclear engineering, materials science, cultural heritage, and industrial applications. Reconstruction of the attenuation matrix for neutron tomography with a traditional analytical algorithm requires hundreds of projection views in the range of 0° to 180° and typically takes several hours to complete. Such a low time-resolved resolution degrades the quality of neutron imaging. Decreasing the number of projection acquisitions is an important approach to improve the time resolution of images; however, this requires efficient reconstruction algorithms. Therefore, sparse-view reconstruction algorithms in neutron tomography need to be investigated. In this study, we investigated the three-dimensional reconstruction algorithm for sparse-view neutron CT scans. To enhance the reconstructed image quality of neutron CT, we propose an algorithm that uses OS-SART to reconstruct images and a split Bregman to solve for the total variation (SBTV). A comparative analysis of the performances of each reconstruction algorithm was performed using simulated and actual experimental data. According to the analyzed results, OS-SART-SBTV is superior to the other algorithms in terms of denoising, suppressing artifacts, and preserving detailed structural information of images.

The fast X-ray imaging beamline (BL16U2) at Shanghai Synchrotron Radiation Facility (SSRF) is a new beamline that provides X-ray micro-imaging capabilities across a wide range of time scales, spanning from 100 ps to μs and ms. This beamline has been specifically designed to facilitate the investigation of a wide range of rapid phenomena, such as the deformation and failure of materials subjected to intense dynamic loads. In addition, it enables the study of high-pressure and high-speed fuel spray processes in automotive engines. The light source of this beamline is a cryogenic permanent magnet undulator (CPMU) that is cooled by liquid nitrogen. This CPMU can generate X-ray photons within an energy range of 8.7–30 keV. The beamline offers two modes of operation: monochromatic beam mode with a liquid nitrogen-cooled double-crystal monochromator (DCM) and pink beam mode with the first crystal of the DCM out of the beam path. Four X-ray imaging methods were implemented in BL16U2: single-pulse ultrafast X-ray imaging, microsecond-resolved X-ray dynamic imaging, millisecond-resolved X-ray dynamic micro-CT, and high-resolution quantitative micro-CT. Furthermore, BL16U2 is equipped with various in situ impact loading systems, such as a split Hopkinson bar system, light gas gun, and fuel spray chamber. Following the completion of the final commissioning in 2021 and subsequent trial operations in 2022, the beamline has been officially available to users from 2023.

The dynamics beamline (D-Line), which combines synchrotron radiation infrared spectroscopy (SR-IR) and energy-dispersive X-ray absorption spectroscopy (ED-XAS), is the first beamline in the world to realize concurrent ED-XAS and SR-IR measurements at the same sample position on a millisecond time-resolved scale. This combined technique is effective for investigating rapid structural changes in atoms, electrons, and molecules in complicated disorder systems, such as those used in physics, chemistry, materials science, and extreme conditions. Moreover, ED-XAS and SR-IR can be used independently in the two branches of the D-Line. The ED-XAS branch is the first ED-XAS beamline in China, which uses a tapered undulator light source and can achieve approximately 2.5 × 10¹² photons/s·300 eV BW@7.2 keV at the sample position. An exchangeable polychromator operating in the Bragg-reflection or Laue-transmission configuration is used in different energy ranges to satisfy the requirements for beam size and energy resolution. The focused beam size is approximately 3.5 μm (H) × 21.5 μm (V), and the X-ray energy range is 5–25 keV. Using one- and two-dimensional position-sensitive detectors with frame rates of up to 400 kHz enables time resolutions of tens of microseconds to be realized. Several distinctive techniques, such as the concurrent measurement of in situ ED-XAS and infrared spectroscopy, time-resolved ED-XAS, high-pressure ED-XAS, XMCD, and pump-probe ED-XAS, can be applied to achieve different scientific goals.

Capacitors are widely used in pulsed magnet power supplies to reduce ripple voltage, store energy, and decrease power variation. In this study, DC-link capacitors in pulsed power supplies were investigated. By deriving an analytical method for the capacitor current on the H-bridge topology side, the root-mean-square value of the capacitor current was calculated, which helps in selecting the DC-link capacitors. The proposed method solves this problem quickly and with high accuracy. The current reconstruction of the DC-link capacitor is proposed to avoid structural damage in the capacitor’s current measurement, and the capacitor’s hotspot temperature and temperature rise are calculated using the FFT transform. The test results showed that the error between the calculated and measured temperature increases was within 1.5 (^circ hbox {C}). Finally, the lifetime of DC-link capacitors was predicted based on Monte Carlo analysis. The proposed method can evaluate the reliability of DC-link capacitors in a non-isolated switching pulsed power supply for accelerators and is also applicable to film capacitors.

To validate the design rationality of the power coupler for the RFQ cavity and minimize cavity contamination, we designed a low-loss offline conditioning cavity and conducted high-power testing. This offline cavity features two coupling ports and two tuners, operating at a frequency of ({162.5},textrm{MHz}) with a tuning range of ({3.2},textrm{MHz}). Adjusting the installation angle of the coupling ring and the insertion depth of the tuner helps minimize cavity losses. We performed electromagnetic structural and multiphysics simulations, revealing a minimal theoretical power loss of ({4.3},{%}). However, when the cavity frequency varied by ({110},textrm{kHz}), theoretical power losses increased to ({10},{%}), necessitating constant tuner adjustments during conditioning. Multiphysics simulations indicated that increased cavity temperature did not affect frequency variation. Upon completion of the offline high-power conditioning platform, we measured the transmission performance, revealing a power loss of ({6.3},{%}), exceeding the theoretical calculation. Conditioning utilized efficient automatic range scanning and standing wave resonant methods. To fully condition the power coupler, a ({15}^circ) phase difference between two standing wave points in the conditioning system was necessary. Notably, the maximum continuous wave power surpassed ({20},textrm{kW}), exceeding the expected target.

The Very Large Area gamma-ray Space Telescope (VLAST) is a mission concept proposed to detect gamma-ray photons through both Compton scattering and electron–positron pair production mechanisms, thus enabling the detection of photons with energies ranging from MeV to TeV. This project aims to conduct a comprehensive survey of the gamma-ray sky from a low-Earth orbit using an anti-coincidence detector, a tracker detector that also serves as a low-energy calorimeter, and a high-energy imaging calorimeter. We developed a Monte Carlo simulation application of the detector using the GEANT4 toolkit to evaluate the instrument performance, including the effective area, angular resolution, and energy resolution, and explored specific optimizations of the detector configuration. Our simulation-based analysis indicates that the current design of the VLAST is physically feasible, with an acceptance above 10 (mathrm m^2, text{sr}) which is four times larger than that of the Fermi-LAT, an energy resolution better than 2% at 10 GeV, and an angular resolution better than 0.2(^circ) at 10 GeV. The VLAST project promises to make significant contributions to the field of gamma-ray astronomy and enhance our understanding of the cosmos.

This paper presents a superhydrophobic melamine (ME) sponge (ME-g-PLMA) prepared via high-energy radiation-induced in situ covalent grafting of long-alkyl-chain dodecyl methacrylate (LMA) onto an ME sponge for efficient oil–water separation. The obtained ME-g-PLMA sponge had an excellent pore structure with superhydrophobic (water contact angle of (154^circ)) and superoleophilic properties. It can absorb various types of oils up to 66–168 times its mass. The ME-g-PLMA sponge can continuously separate oil slicks in water by connecting a pump or separating oil underwater with a gravity-driven device. In addition, it maintained its highly hydrophobic properties even after long-term immersion in different corrosive solutions and repeated oil adsorption. The modified ME-g-PLMA sponge exhibited excellent separation properties and potential for oil spill cleanup.

The sensitivity of the dark photon search through invisible decay final states in low-background experiments relies significantly on the neutron and muon veto efficiencies, which depend on the amount of material used and the design of the detector geometry. This paper presents the optimized design of the hadronic calorimeter (HCAL) used in the DarkSHINE experiment, which is studied using a GEANT4-based simulation framework. The geometry is optimized by comparing a traditional design with uniform absorbers to one that uses different thicknesses at different locations on the detector, which enhances the efficiency of vetoing low-energy neutrons at the sub-GeV level. The overall size and total amount of material used in the HCAL are optimized to be lower, owing to the load and budget requirements, whereas the overall performance is studied to satisfy the physical objectives.