Nuclear Analysis最新文献

FENGHUANG diffractometer at CMRR, a high-intensity multi-section neutron powder diffractometer, has been constructed to in situ studies of materials under high pressure high temperature conditions. With development of anvils, high pressure high temperature cell assemblies, high pressure device and alignment system, we have been realized the angle-dispersive neutron diffraction data collect at the range of achievable pressures and temperatures of 0–30 GPa and 300–1500 K, with the sample size of millimeter scale. This paper describes the technical characteristics of diffractometer and related techniques for high pressure neutron diffraction experiments, and gives some scientific examples that have been recently performed on FENGHUANG. The experience gained experiments on FENGHUANG could help promote the development of high pressure techniques on neutron scattering facilities.

Containerless processing is able to access the deeply supercooled regime due to the absence of heterogeneous nucleation sites, for example, container walls. Therefore, it allows us to explore a possible structural transition in the supercooled state, which is usually hidden by crystallization and difficult to detect with conventional methods. CoCrFeNi high entropy alloys (HEAs) were solidified in aerodynamic levitation containerless processing in Nanoscale-ordered Materials Diffractometer (NOMAD) BL-1B instrument at Spallation Neutron Source (SNS) Oak Ridge National Lab with expectation the distinct local ordering in CoCrFeNi HEAs. The temperature dependence of local structures was investigated from room temperature to 1500 °C on NOMAD. The phase evolution of the CoCrFeNi HEA investigated using in-situ neutron diffraction shows that room temperature face-centered cubic (fcc) phase is inherited from its high-temperature (above 1400 °C) fcc cluster.

Mass spectrometry techniques, such as AMS, TIMS and ICP-MS, represent promising techniques for the analysis of artificial radionuclides in environmental samples. They are characterized by high sensitivity, low detection limit, high sample throughput, shorter measuring time compared to conventional radiometric measurements, and the capability to provide isotopic composition information. After the Fukushima Daiichi Nuclear Power Plant accident, an increasing need was recognized for the rapid analysis of accident-released artificial radionuclides (actinides and fission products) in environmental samples for radiation dose estimation and evaluation of effectiveness of radioactive contamination remediation. This review describes the recent progress on mass spectrometric analysis of artificial radionuclides in environmental samples in Japan after the nuclear accident and discusses future research prospects for mass spectrometric techniques in radionuclide analysis.

Origin assessment of nuclear materials is the key aim of nuclear forensics. Among the various fingerprints, rare-earth elements (REEs) are regarded as a powerful geological signature in authentication studies as they behave similarly during geologic and mining/milling processes. In this study, the combination of rare-earth impurities and Nd–Ce isotope ratios were proposed as a novel fingerprint for the origin assessment of uranium ores. A database was established, comprising mass spectrometric measurements of rare-earth elemental parameters of twenty-five samples from seven countries. The efficiencies of different multivariate statistical techniques, including cluster analysis (CA), principal component analysis (PCA) and linear discriminant analysis (LDA), were compared. The results showed that most of uranium ore samples were correctly classified according to geographical origins, and Nd–Ce isotope ratios played a key role in improving the classification. High recognition (100%) and satisfactory predictive ability (90%) of the developed LDA model proved that the proposed method is a powerful tool for tracing unknown uranium ore samples.

This novel double heterojunction carbon quantum dots (CQDs)/CeO₂/BaFe₁₂O₁₉ magnetic separation photocatalysts (CCBFOMSPs) were successfully prepared via a polyacrylamide gel method and low temperature sintering technology combined with a hydrothermal method. The CQDs components in CCBFOMSPs were identified by neutron powder diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy. The charge carriers could transfer and separation between the valence state components (CeO₂ and BaFe₁₂O₁₉) and CQDs facilely, inhibiting the recombination of electron-hole pairs significantly by Hall effect. The photocatalytic activity of CCBFOMSPs for the degradation of mixed dyes include methyl orange (MO), rhodamine B (RhB) and methylene blue (MB) and tetrabromobisphenol A (TBBPA) were remarkably improved by regulating the electromagnetic interaction between the BaFe₁₂O₁₉ contents and the photo-generated electrons. Capturing experiment showed that the active species of hole (h_VB⁺), hydroxyl radical (•OH) and superoxide radical (•O₂⁻) played dominant roles in mixed dyes degradation. Attractively, the effect shed new light on wide applications of the double heterojunction magnetic separation photocatalysts.

The kinetic equation including the reflected neutron effect is established based on the time-dependent two-region kinetic model. Different reactivity measurement methods are simulated by using the equation. The simulation results show the difference of estimated reactivity values between the prompt neutron decay constant method and the positive period method. It illustrates the principle of reactivity difference in measured value by using different measurement methods, that is, the time scale of the measurement method determines the contribution rate of the reflected neutrons in the experiments. The contribution rate influences the measured value of reactivity.

Secondary electron detector (SED) is a key component used in the fission product yield experiment to mark the start time of fission events. The signal to noise ratio and timing characteristics has an important impact on the mass resolution for measuring fission fragments. In this paper, a novel design of secondary electron detector based on MCP was proposed to measure the secondary electrons emitted from fission target. Based on the alpha particles and the fission fragments emitted from ²⁵²Cf source, the response of SED and SCVD diamond are obtained by using a digitizer of 10 bit and 1 ​G samples/s. The rise time of alpha particles and fission fragments are 1.8 ns and 1.7 ns, while the pulse width of which is 4.5 ns and 9.7 ns, respectively. Using the time of flight method and digital constant fraction algorithm, the time resolution of "SED ​+ ​sCVD diamond detector" system for 6.1 ​MeV alpha particles from ²⁵²Cf is obtained as 242 ± 4.7 ps, while that of SED detector is about 171 ± 2.4 ps. The total transition length and time of secondary electron (SE) in the detector are 15.79 cm and 5.97 ns, respectively.

To achieve efficient design and accurate simulation of neutron spin flipping, a fast numerical calculation method was introduced to facilitate the processes parameter optimization and flipper design. Magnetic field models and measured magnetic data can be directly imported into the simulation. To test the proposed new simulation software, three experimental examples were performed and compared with the measured data. The software developed showed good accuracy.

Radiation target theory refers to that ionizing radiation hits specific molecules or organellaes in cells, resulting in structural damage, gene mutation, chromosome breakage and other target effects of biological macromolecules. It is the most widely accepted theory in radiobiology, radiotherapy and radiation protection. Based on this theory, several different mathematical models have been proposed to evaluate the cell killing effect in radiotherapy and radiation risk assessment. In addition, the target(s)-related technologies have also been well developed. Here, we review the development of radiation target theory and mathematical models, focusing on the related researches on three key biological radiation targets: DNA, protein and lipid. Alternatively, improvements in physical radiation technology based on radiation targets and developments in biotechnology (e.g., omics analysis, chromatin conformation analysis, and the application of organoid models) are described. This review provides insights for a better understanding of the roles of targeting effects in radiobiology, and emphasizes the application value of target-related techniques in clinical treatment.

Niobium is one of the most important neutron dosimeters used outside of the reactor. Owing to the fluorescence effects of ¹⁸²Ta and ⁹⁴Nb radionuclides, it is a problem to quickly obtain the activity of ^93mNb which produced by the neutron inelastic scattering of Nb. To solve this problem, a fast estimating method based on the Monte Carlo simulation is proposed. All the contributions from fluorescence effects that induced by gamma-rays, beta-rays and internal conversion electrons of the radionuclides in the niobium sample were considered. The comparison results demonstrated that the deviation is less than 8.0% between the calculated and the experimental activities. It shows that the contribution of radionuclide by fluorescence effects in activity measurement of the niobium sample can be subtracted quickly using this method, based just once experimental measurement.