α-Fe／Nd2Fel4B复合纳米晶的界面研究

采用正电子寿命谱和双探头Doppler展宽测量在原子尺度上研究了α-Fe，Nd2Fel4B复合纳米晶的界面结构。正电子寿命研究表明，α-Fe/Nd2Fel4B复合纳米晶存在两类界面。一类为非晶界面层，正电子湮没寿命为155ps；另一类为具有原子空位的松懈界面，含有空位尺寸大于-2个铁原子空位的结构自由体积，正电子湮没寿命为246ps。电子-正电子湮没光子的共谐Doppler展宽测量表明这类松懈界面富集非磁性原子Nd和B，这将削弱α-Fe/Nd2Fel4B复合纳米晶晶粒间的磁交换耦合。     

正电子湮没与沸石内静电场

本文测定了不同类型沸石的正电子寿命谱。发现o-Ps的湮没寿命, 与沸石静电场之间有良好的对应关系, 静电场愈强, 湮没寿命愈短。根据正电子寿命谱结果。含不同阳离子的Y沸石的静电场强弱次序为KY相似文献   

液晶相变的微结构研究

用正电子湮没和差示扫描量热(DSC)变温测量液晶(EBBA)样品的正电子湮没寿命谱及DSC曲线,结果表明正电子湮没的短寿命(τ_s)基本不变,而长寿命(τ₁)和强度(I₁)明显地有两次跳变,其跳变的温度范围与DSC所测定的相转变温度范围基本一致,在加热和冷却过程中样品在晶体相←→向列相之间的相互转变的相转变温度范围显著不同。用正电子湮没的ORE模型讨论了由于液晶相转变所引起的微结构变化,从而提出正电子是研究液晶(EBBA)相变的探针。 关键词：     

Optical Potential Calculations of Positron-H2 Elastic Collision

We report the calculations of the elastic scattering differential cross section for positron H2 collisions with the impact energy below the positronium formation threshold. Our calculation is based on the static-exchange-optical model which has obtained great success in the case of electron scattering. The effective potential used here includes the static and optical potentials. The optical method can completely include the second-order effect arising from real and virtual excitation of target states, which is important for the scattering. A comparison is made with the available theoretical calculations.     

La2-xBaxCuO4超导体的PAT研究

本文报道了在室温下对La2-xBaxCuO4超导系列样品的正电子寿命谱（PAT）测量，讨论了正电子湮没机制与超导转变温度的关联，并从电子密度转移方面解释了La2-xBaxCuO4超导样品在1／8处的转变温度受抑制的原因．     

Ion Beam Analysis of the Annealing Behavior of Helium in Ti Films

We present a theoretical calculation finding that a spectrum from ion beam analysis will change at different stopping cross sections. This is more visible at a deeper place in the sample. Helium-contained Ti films annealed at different temperatures are prepared to gain different stopping cross sections whereby the stopping cross section will change with the helium phase states and the pressure of helium bubbles. Then ion beam analysis is used to measure the concentration of helium. It is found that the concentration curve rises greatly after the sample is annealed at 673K which reflects the increasing size of the helium bubble. The results axe consistent with that of positron annihilation radiation spectra which are performed by using a changeable energy positron beam.     

介孔SiO2薄膜孔结构的慢正电子技术表征

通过蒸发诱导自组装技术制备了具有不同有序结构的介孔SiO₂薄膜,并采用同步辐射X射线反射率以及慢正电子束流技术对其进行表征.实验结果表明,随着旋涂速率的增加,介孔结构由三维立方向二维六角结构转变,同时平均孔隙率随转速增加而减小.利用各向同性无机孔收缩模型和Fourier变换红外光谱,探讨了薄膜结构和正电子湮没参数的内在联系. 关键词： 同步辐射 X射线反射率 Doppler展宽 正电子素飞行时间谱     

正电子寿命-动量关联技术

评述了国际正电子领域的新探测技术———寿命 动量关联技术.介绍了该技术的发展过程,讨论了该技术的分析方法,详细阐述了该技术在Ps形成和热化过程中的应用,并讨论了该技术在Ps化学上的应用.A new detection technique--age momentum correlation in international positron field is reviewed. The recent development is described and the analysis methods are discussed for the technique. The application of the technique in the positronium formation and thermalization processes are systematically summarized. Besides the application of the technique in Ps chemistry is discussed.     

Dephasing time of a positron accelerated by a laser pulse

The dephasing time of a positron in the total field associated with a laser pulse in a plasma J28is studied numerically. It is shown that the dynamics of the positron is quite different from that of an electron due to the electrostatic potential in the body of the pulse. The dephasing time of the positron increases with the pulse length and decreases with the pulse intensity nonlinearly. In the long pulse case (L》λ_p) the dephasing time is proportional to the pulse length. These results provide a scientific basis for experiments to observe the positron acceleration scheme, and may be important to the physics of laser-article interactions in multi-component plasmas.