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排序方式: 共有196条查询结果,搜索用时 0 毫秒
61.
从252Cf自发裂变中子源之裂变中子在时间分布上相互独立的基本原理出发,针对随机核信号在时间上呈泊松分布,在幅度上服从高斯分布的这一特征,开展了基于FPGA技术的仿252Cf中子源随机核信号产生及其频谱分析系统的研究.通过比较仿252Cf中子源核信号与核信号的功率谱趋势,验证了仿252Cf中子源随机信号产生机制的可靠性... 相似文献
62.
M.N. Nasrabadi F. BakhshiM. Jalali A. Mohammadi 《Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment》2011,659(1):378-382
Nuclear-based explosive detection methods can detect explosives by identifying their elemental components, especially nitrogen. Thermal neutron capture reactions have been used for detecting prompt gamma 10.8 MeV following radioactive neutron capture by 14N nuclei. We aimed to study the feasibility of using field-portable prompt gamma neutron activation analysis (PGNAA) along with improved nuclear equipment to detect and identify explosives, illicit substances or landmines. A 252Cf radio-isotopic source was embedded in a cylinder made of high-density polyethylene (HDPE) and the cylinder was then placed in another cylindrical container filled with water. Measurements were performed on high nitrogen content compounds such as melamine (C3H6N6). Melamine powder in a HDPE bottle was placed underneath the vessel containing water and the neutron source. Gamma rays were detected using two NaI(Tl) crystals. The results were simulated with MCNP4c code calculations. The theoretical calculations and experimental measurements were in good agreement indicating that this method can be used for detection of explosives and illicit drugs. 相似文献
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64.
X.D. Lu J. Ning C.Y. Deng Q. Qiu Zhang Chuanwu Jiang Ming 《Nuclear instruments & methods in physics research. Section B, Beam interactions with materials and atoms》2009,267(18):3238-3241
The deposition of polyatomic C2H5+ ions is studied using classical molecular dynamics simulations with a new improved Brenner potentials developed by Brenner. The simulation results show that when the incident energy is less than 65 eV, the deposition coefficient of H is larger than that of C atoms. When the incident energy is larger than 65 eV, the deposition of H is less than that of C atoms. With increasing incident energy, a transition from Csp3-rich to Csp2-rich in the grown films is found. 相似文献
65.
Jinjin Yao Shengyang Pang Yuanhong Wang Chenglong Hu Rida Zhao Jian Li Sufang Tang Hui-Ming Cheng 《金属学报(英文版)》2022,35(5):801
C/SiC volume ratios in carbon fiber-reinforced carbon-silicon carbide (Cf/C-SiC) composites may influence greatly mechanical and oxidation properties of the composites, but have not been well investigated yet. Herein, Cf/C-SiC composites with different C/SiC volume ratios were fabricated by chemical vapor infiltration (CVI) technique through alternating the thickness of a pyrocarbon (PyC) interlayer. The composites with C/SiC volume ratios of 0.37 and 0.84 exhibited the better comprehensive mechanical properties. The CS0.37 showed the highest flexural strength of 340.6 MPa, and CS0.84 had the maximum tensile strength of 139.1 MPa. The excellent mechanical properties were closely related to the relatively low C/SiC volume ratios and porosities, optimum interfacial bonding and reduced matrix micro-cracks. The composite with a low C/SiC volume ratio of 0.10 showed the best anti-oxidation performance due to its high SiC content. The oxidation mechanisms at 1100 °C and 1400 °C were discussed by considering the effect of the C/SiC volume ratios, pores and matrix micro-cracks, oxidation of carbon phase and SiC. 相似文献
66.
采用Cl2/Ar感应耦合等离子体(ICP)对单晶硅进行了刻蚀,工艺中用光刻胶作掩膜。研究了气体组分、ICP功率和RF功率等工艺参数对硅刻蚀速率和硅与光刻胶刻蚀选择比的影响,同时还研究了不同工艺条件对侧壁形貌的影响。结果表明,由于物理刻蚀机制和化学刻蚀机制的相对强度受到混合气体中Cl2和Ar比例的影响,硅刻蚀速率随着Ar组分的增加而降低,同时选择比也随之降低。硅刻蚀速率随着ICP功率的增大先增大继而减小,选择比则成上升趋势。硅刻蚀速率和选择比均随RF功率的增大单调增大。在Cl2/Ar混合气体的刻蚀过程中,离子辅助溅射是决定硅刻蚀效果的重要因素。同时,文中还研究分析了刻蚀工艺对于微槽效应和刻蚀侧壁形貌的影响,结果表明,通过提高ICP功率可以有效减小微槽和平滑侧壁。进一步研究了SiO2掩膜下,压强改变对于硅刻蚀形貌的影响,发现通过降低压强,可以明显地抑制杂草的产生。 相似文献
67.
ABSTRACT: We report a novel synthesis of porous PbSe layers on Si substrates using anodic electrochemical treatment of PbSe/CaF2/Si(111) epitaxial structures in an electrolyte solution based on glacial acetic acid and nitric acid. Electron microscopy, x-ray diffractometry, and local chemical microanalysis investigations results for the porous layers are presented. Average size of the synthesized mesopores with ~1010 cm-2 surface density was determined to be 22 nm. The observed phenomenon of the active selenium redeposition on the mesopore walls during anodic treatment is discussed. 相似文献
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69.
Long Xia Shengpeng Hu Hua Yang Hong Bian Ke Wang Xiaoxiao Huang Xiaoguo Song 《International Journal of Applied Ceramic Technology》2019,16(3):907-916
In this paper, carbon fiber reinforced lithium aluminosilicate (LAS) glass-ceramics matrix composites (Cf/LAS composites) are joined to Ti60 alloy using TiZrNiCu + Cf mixed powders by proper process parameters. The carbon fibers distribute uniformly in the brazing interlayer and react with Ti, Zr elements in the brazing alloy to form (Ti, Zr)C thin reactive layers, which are between the carbon fibers and the Ti, Zr elements. The effect of Cf content on the mechanical properties and microstructure of brazed joints are investigated. The microstructure of brazed joints varied obviously with the increasing of Cf content. The thickness of reactive layer between interlayer and Cf/LAS composites and Ti solid solution (Ti (s.s)) decrease gradually, and the volume of eutectic structure (Ti(s,s) + (Ti,Zr)2(Ni,Cu)) decrease gradually. The obtained brazed joints exhibit a maximum shear strength of 73.5 MPa at room temperature using TiZrNiCu + 0.3 wt% Cf mixed powders. The enhanced shear strength can be attributed to the reduction in thermal stress and the reinforcing effect originated from the carbon fiber addition. 相似文献
70.