Institutional Repository of Institute of Modern Physics, CAS
Not a member yet
5769 research outputs found
Sort by
Surface and structure modification induced by high energy and highly charged uranium ion irradiation in monocrystal spinel
No full textDue to its high temperature properties and relatively good behavior under irradiation, magnesium aluminate spinel (MgAl2O4) is considered as a possible material to be used as inert matrix for the minor actinides burning. In this case, irradiation damage is an unavoidable problem. In this study, high energy and highly charged uranium ions (290 MeV U32+) were used to irradiate monocrystal spinel to the fluence of 1.0 x 10(13) ions/cm(2) to study the modification of surface and structure. Highly charged ions carry large potential energy, when they interact with a surface, the release of potential energy results in the modification of surface. Atomic force microscopy (AFM) results showed the occurrence of etching on surface after uranium ion irradiation. The etching depth reached 540 nm. The surprising efficiency of etching is considered to be induced by the deposition of potential energy with high density. The X-ray diffraction results showed that the (440) diffraction peak obviously broadened after irradiation, which indicated that the distortion of lattice has occurred. After multi-peak Gaussian fitting, four Gaussian peaks were separated, which implied that a structure with different damage layers could be formed after irradiation. (c) 2014 Elsevier B.V. All rights reserved
Tailoring the size and distribution of Ag nanoparticles in silica glass by defects
No full textThe composites embedded with metallic nanoparticles show large nonlinear optical susceptibility and strong surface plasmon resonance absorption, which enable potential application in opto-electronics. Ion implantation has been proven to be a powerful technique of synthesis of metallic nanoparticles due to its versatility and compatibility. However, the synthesis of nanoparticles by ion implantation inevitably leads to a broad size distribution due to Ostwald ripening process. The broad size distribution has a negative effect on improving the figure of merits for nonlinear optics. In this paper, we tried to introduce defects in silica glass to act as pre-nucleation centers to mediate the size and distribution of Ag nanoparticles. In experiment, the silica glass samples were pre-irradiated by 200 key Ar ions to fluences of 0.8, 2.0 and 5.0 x 10(16) ions/cm(2), and then 200 keV Ag ions were implanted into the pre-irradiated samples to fluence of 2.0 x 10(16) ions/cm(2). UV-VIS results show that the absorbance intensity of Ag SPR peak initially increases and then decreases with pre-irradiation fluence, which implies the change in size and density of Ag nanoparticles in samples. TEM results verify that Ag nanoparticles in the sample pre-irradiated to the fluence of 0.8 x 10(16) ions/cm(2) grow bigger and distribute in a relatively narrow region comparing with that without pre-irradiation. With further increase of pre-irradiation fluence, the size of Ag nanoparticles shows a depth dependent distribution. A boundary can be clear seen at the depth of 110 nm, larger Ag nanoparticles disperse in region shallower than 110 nm, and smaller Ag nanoparticles disperse in the region deeper than 110 nm. The average size of Ag nanoparticles initially increases and then decreases with pre-irradiation fluence. Therefore, the introduction of defects by pre-irradiation could be an effective way to tailor the size and distribution of metallic nanoparticles in matrix. (C) 2013 Elsevier B.V. All rights reserved
Primary isotope yields and characteristic properties of the fragmenting source in heavy-ion reactions near the Fermi energy
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">For central collisions of Ca-40 + Ca-40 at 35 MeV/nucleon, the density and temperature of a fragmenting source have been evaluated in a self-consistent manner using the ratio of the symmetry energy coefficient relative to the temperature, a(sym)/T, extracted from the yields of primary isotopes produced in antisymmetrized molecular dynamics (AMD) simulations. The a(sym)/T values are extracted from all isotope yields using an improved method based on the modified Fisher model (MFM). The values of a(sym)/T obtained, using different interactions with different density dependencies of the symmetry energy term, are correlated with the values of the symmetry energies at the density of fragment formation. Using this correlation, the fragment formation density is found to be rho/rho(0) = 0.67 +/- 0.02. Using the input symmetry energy value for each interaction temperature values are extracted as a function of isotope mass A. The extracted temperature values are compared with those evaluated from the fluctuation thermometer with a radial flow correction.</span
Progress of a room temperature electron cyclotron resonance ion source using evaporative cooling technology at Institute of Modern Physics
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">A new room temperature ECR ion source, Lanzhou Electron Cyclotron Resonance ion source No. 4 (LECR4, previously named DRAGON), is under intense construction at Institute of Modern Physics. LECR4 is designed to operate with 18 GHz microwave frequency. The maximum axial magnetic fields are 2.3 T at injection and 1.3 T at extraction, and the radial field at the plasma chamber wall of 76 mm inner diameter is 1.0-1.2 T. One of the unique features for LECR4 is that its axial solenoids are winded with solid square copper wires which are immersed in a kind of special evaporative cooling medium for cooling purpose. Till now, a prototype of the cooling system has been successfully constructed and tested, which has demonstrated that the cooling efficiency of the designed system could meet the requirements of LECR4 under the routine operation conditions. All the main components of the ion source have been completed. Assembly and commissioning is ongoing. The latest developments and test results will be presented in this paper. (C) 2013 AIP Publishing LLC.</span
Study on Thermal Sho ck Damage to Injector IIof China ADS Project
No full text<span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">由于束流脉冲无法控制而引起直线加速器的热冲击损伤是造成加速器无法完成聚束及偏转的主要因素,而对热冲击进行定量的热应力评估可以有效地避免RFQ、超导腔以及其他加速元件等加速器设备的损伤,这在研制强流直线加速器的过程中至关重要。本研究引用一种新颖的计算方法定量分析整个注入器的热冲击损伤并明确了三种不同材料高纯铌、无氧铜和不锈钢对应的加速器件的热冲击的特征。基于有限元方法对瞬态热应力进行分析,得出三种不同材料对应的加速器件在入射角度为90度时的温度分析结果。对于所研制的注入能量低于10 MeV的强流直线加速器来讲,得到可允许的入射时间为20mus。</span><span style="color: rgb(51, 51, 51); font-family: arial, helvetica, sans-serif; font-size: 13px; line-height: 22px; background-color: rgb(248, 248, 248);">Because of injecting an out-of-control beam pulse, thermal shock damage to the accelerator may well cause a failure of focusing and steering elements. In order to prevent RFQ accelerator, superconducting cavities and other accelerator components from thermal damage, it is essential to conduct a quantitative evaluation of the thermal stresses induced in the material during the thermal shock. The present study in this paper proposed a novel method to evaluate the thermal stresses quantitatively, which can clarify the characteristics of thermal shock of several materials, such as OFHC, SUS304 and Niobium. Transitional thermal stress is investigated by three dimensional finite element method (FEM) to obtain the temperature distribution for three materials at the beam incident angle of 90°. Finally the simulation results prove that the machine protect system response time meets the requirement when the allowable injection time is defined as 20 mus.</span
