A new positron annihilation lifetime spectrometer based on DRS4 waveform digitizing board

A new simple digital positron lifetime spectrometer has been developed. It includes a DRS4 waveform digitizing board and two scintillation detectors based on the XP2020Q photomultiplier tubes and LaBr₃ scintillators. The DRS4 waveform digitizing can handle small pulses, down to few tens of millivolts, and its time scale linearity and stability are very good. The new system has reached a 206 ps time resolution, which is better than the conventional analog apparatus using the same detectors. These improvements make this spectrometer more simple and convenient in comparison with other spectrometers, and it can be applied to the other scintillation timing measurements with picosecond accuracy.     

利用分光光度计研究玻璃PLOT柱载体层涂敷技术

有机胶法制备多孔层开管柱(PLOT柱),是中国科学院兰州化学物理研究所提出的一种具有我国特点的制柱方法。该法已在我国得到推广。这种制柱方法的关键步骤在于载体层涂敷,其它步骤均与制备壁涂开管柱相同。在制柱中,无论“先拉后涂”还是“先涂后拉”,都必须力求涂层均匀,多孔层增厚,以提高柱效和样品负荷量。该所利用扫描电镜观察涂有效果,而一般实验室则只靠肉眼观察。我们按文献进行玻管涂敷,利用改装的     

修正屏蔽库仑势下二维尘埃等离子体的动力学和结构特性

本文考虑等离子体密度分布变化, 得到了修正屏蔽库仑势的解析解. 数值分析以及分子动力学模拟表明, 在常见实验室参数情况下, 等离子体密度分布变化引起的屏蔽库仑势修正对二维尘埃等离 子体系统的动力学和结构特性影响很小. 在极限参数情况下, 本模型的计算结果表明二维尘埃等离子体系统的扩散能力明显降低, 并且系统组态呈圆形分布. 此外, 本文还研究了实验室常见大小磁场对二维尘埃等离子体系统的影响. 关键词： 修正屏蔽库仑势 二维尘埃等离子体 分子动力学模拟     

A new positron annihilation lifetime spectrometer based on DRS4 waveform digitizing board

Abstract： A new simple digital positron lifetime spectrometer has been developed. It includes a DRS4 waveform digitizing board and two scintillation detectors based on the XP2020Q photomultiplier tubes and LaBr3 scintillators. The DRS4 waveform digitizing can handle small pulses, down to few tens of millivolts, and its time scale linearity and stability are very good. The new system has reached a 206 ps time resolution, which is better than the conventional analog apparatus using the same detectors. These improvements make this spectrometer more simple and convenient in comparison with other spectrometers, and it can be applied to the other scintillation timing measurements with picosecond accuracy.     

The application of artificial neural networks to the inversion of the positron lifetime spectrum

A new method of processing positron annihilation lifetime spectra is proposed.It is based on an artificial neural network(ANN)-back propagation network(BPN).By using data from simulated positron lifetime spectra which are generated by a simulation program and tested by other analysis programs,the BPN can be trained to extract lifetime and intensity from a positron annihilation lifetime spectrum as an input.In principle,the method has the potential to unfold an unknown number of lifetimes and their intensities from a measured spectrum.So far,only a proof-of-principle type preliminary investigation was made by unfolding three or four discrete lifetimes.The present study aims to design the network.Besides,the performance of this method requires both the accurate design of the BPN structure and a long training time.In addition,the performance of the method in practical applications is dependent on the quality of the simulation model.However,the chances of satisfying the above criteria appear to be high.When appropriately developed,a trained network could be a very efficient alternative to the existing methods,with a very short identification time.We have used the artificial neural network codes to analyze data such as the positron lifetime spectra for single crystal materials and monocrystalline silicon.Some meaningful results are obtained.     

金属的正电子双多普勒展宽谱研究

研制了一套数字化的正电子湮没双多普勒展宽谱测量系统,用它测量了10个样品的双多普勒展宽谱,得到了一些有意义的结果.这些结果展示了一些金属单质材料的双多普勒展宽谱随着电子结构变化而发生的变化.本文简略介绍了双多普勒展宽谱仪,实验数据处理,以及这些金属单质材料的数据和分析结果.     

变截面长柱双机三点吊最优吊点的研究分析

根据变截面钢筋混凝土长柱吊装的实际工程需要，进行了双机三点吊吊装方案的研究分析，建立了双机二点吊吊装方案的数学模型，编制了微机软件，解决了变截面钢筋混凝土长柱双机三点吊中的难题