名义组分为Y_6Ba_(11)Cu_(16)O_x的纳米超导材料

采用柠檬酸盐热分解法制备了名义组分为Y6Ba11Cu16Ox的纳米超导材料。利用XRD对其粉体进行物相表征,发现其相是Y123和Y211的混合相,并测得两者之间的摩尔比为1∶0.14,同时把其XRD图谱与Y1Ba2Cu3O7-x的XRD图谱进行了对照分析。利用标准的四端引线法对其块体进行R-T分析,测出其起始转变温度Tonset=86.0K,转变宽度△Tc=6.7K,并表现出良好的超导电性,也相应地把其与Y1Ba2Cu3O7-x进行了对比。根据Scherrer公式计算得到样品的平均晶粒尺寸约为67.1nm。文中也分析了所制材料为混合物的原因。     

白光LED用蓝绿色荧光粉Sr1-xBax Al2O4:Eu2+的发光性质

采用高温固相法在还原气氛中合成Sr1-xBaxAl2 O4:Eu2+荧光材料.XRD显示,当钡掺杂量x＜0.4时,对应样品主要为单斜SrAl2 O4晶体结构;当x≥0.4时,对应样品主要为简单六方BaAl2 O4晶体结构.在360nn激发下,样品的发射光谱随x的增加由单一的绿光发射(λmax=516nm)逐渐转变为蓝绿...     

Acoustic dipole radiation model for magnetoacoustic tomography with magnetic induction

An acoustic dipole radiation model for magnetoacoustic tomography with magnetic induction (MAT-MI) is pro-posed,based on the analyses of one-dimensional tissue vibration,three-dimensional acoustic dipole radiation and acoustic waveform detection with a planar piston transducer.The collected waveforms provide information about the conductiv-ity boundaries in various vibration intensities and phases due to the acoustic dipole radiation pattern.Combined with the simplified back projection algorithm,the conductivity configuration of the measured layer in terms of shape and size can be reconstructed with obvious border stripes.The numerical simulation is performed for a two-layer cylindrical phantom model and it is also verified by the experimental results of MAT-MI for a tissue-like sample phantom.The proposed model suggests a potential application of conductivity differentiation and provides a universal basis for the further study of conductivity reconstruction for MAT-MI.     

Growth of gem-grade nitrogen-doped diamond crystals heavily doped with the addition of Ba（N3）2

Additive Ba(N 3) 2 as a source of nitrogen is heavily doped into the graphite-Fe-based alloy system to grow nitrogendoped diamond crystals under a relatively high pressure (about 6.0 GPa) by employing the temperature gradient method.Gem-grade diamond crystal with a size of around 5 mm and a nitrogen concentration of about 1173 ppm is successfully synthesised for the first time under high pressure and high temperature in a China-type cubic anvil highpressure apparatus.The growth habit of diamond crystal under the environment with high degree of nitrogen doping is investigated.It is found that the morphologies of heavily nitrogen-doped diamond crystals are all of octahedral shape dominated by {111} facets.The effects of temperature and duration on nitrogen concentration and form are explored by infrared absorption spectra.The results indicate that nitrogen impurity is present in diamond predominantly in the dispersed form accompanied by aggregated form,and the aggregated nitrogen concentration in diamond increases with temperature and duration.In addition,it is indicated that nitrogen donors are more easily incorporated into growing crystals at higher temperature.Strains in nitrogen-doped diamond crystal are characterized by micro-Raman spectroscopy.Measurement results demonstrate that the undoped diamond crystals exhibit the compressive stress,whereas diamond crystals heavily doped with the addition of Ba(N 3) 2 display the tensile stress.     

Synthesis and characterization of p-type boron-doped IIb diamond large single crystals

High-quality p-type boron-doped IIb diamond large single crystals are successfully synthesized by the temperature gradient method in a china-type cubic anvil high-pressure apparatus at about 5.5 GPa and 1600 K.The morphologies and surface textures of the synthetic diamond crystals with different boron additive quantities are characterized by using an optical microscope and a scanning electron microscope respectively.The impurities of nitrogen and boron in diamonds are detected by micro Fourier transform infrared technique.The electrical properties including resistivities,Hall coefficients,Hall mobilities and carrier densities of the synthesized samples are measured by a four-point probe and the Hall effect method.The results show that large p-type boron-doped diamond single crystals with few nitrogen impurities have been synthesized.With the increase of quantity of additive boron,some high-index crystal faces such as {113} gradually disappear,and some stripes and triangle pits occur on the crystal surface.This work is helpful for the further research and application of boron-doped semiconductor diamond.     

低能Ar9+离子与Na原子碰撞反应中的多电子转移过程

利用近代物理研究所新建的原子物理实验平台,采用位置灵敏探测和散射离子-反冲离子飞行时间符合技术,研究了180 keV的Ar9+离子与Na原子碰撞中的多电子转移过程,对实验结果做了分析和简单的讨论,并同修正后的分子库仑过垒模型结果进行了比较.     

氧离子与氦、氖原子碰撞中转移电离过程的研究

采用位置灵敏探测和散射离子-反冲离子飞行时间测量技术,测量了氧离子与氖和氦原子碰撞过程中转移电离截面与单电子俘获截面之比.通过比较发现测量结果与文献结果的趋势一致,并对测量结果进行了讨论.     

Determination of the time resolution for neutron scintillation detectors by multi-coincidence measurement

Based on the multi-coincidence measurement, the time resolution of three liquid scintillation detectors (BC501A) were determined strictly by solving the coincidence equations, where the influence from electronics estimated by self coincidence measurement as well as the background had been considered. The result of this work agreed well with the result that was deduced from the traditional method, and it will be helpful to analyze the energy resolution of neutron time of flight spectra measured by using such detectors at CIAE (China Institute of Atomic Energy).     

Early effect modeling of silicon-on-insulator SiGe heterojunction bipolar transistors

Silicon germanium(SiGe) heterojunction bipolar transistor(HBT) on thin silicon-on-insulator(SOI) has recently been demonstrated and integrated into the latest SOI BiCMOS technology.The Early effect of the SOI SiGe HBT is analysed considering vertical and horizontal collector depletion,which is different from that of a bulk counterpart.A new compact formula of the Early voltage is presented and validated by an ISE TCAD simulation.The Early voltage shows a kink with the increase of the reverse base-collector bias.Large differences are observed between SOI devices and their bulk counterparts.The presented Early effect model can be employed for a fast evaluation of the Early voltage and is useful to the design,the simulation and the fabrication of high performance SOI SiGe devices and circuits.     

Spectra of Highly Ionized Sulfur below 200 ^。A

Spectra of carbon-,boron-,beryllium-,lithium-,helium-,and hydrogen-like sulfur ions were obtained and studied for the wavelengths below 200 ^。A and the energy of 8O Me V by using beam-foil method.Thirty-five lines have been identified,in which 15 lines are newly accurately measured.The spectra were analysed based on the theoretical results and other experimental data.