查询词典 positron

It can be used to identify elements and to analyze the chemical environment in the positron annihilation site.

重点包括谱仪的研制、系统的优化以及测量性能的提高。

Therefore there exist the so called vacuum fluctuations. In the QED, for example, there exist the effects of zero-point oscillations of photons, the effects of vacuum polarization of electron-positron paris, and so on. They all could result in observable consequences , such as the anomalous magnetic moment of the electron, the spontaneous emission of atoms in excited states, the Lamb shift and the Casimir effect, which have been verfied in experiments.

例如，在量子电动力学中真空中存在着光子的真空零点振动效应，正负电子对的真空极化效应等等，它们都导致可观测的物理效果，如磁矩反常、激发态原子自发辐射、兰姆移动、卡西米尔效应等。

So, the antiparticle of the normal electron is called the positron, as it has a positive charge, but the same mass as the electron.

这样，正常电子的反粒子叫做正电子，如同它有一个阳电荷一样，但是与电子的质量一样。

Because the positron annihilation spectroscopy can directly show the information of the defects in the materials, we have measured the positron life of the gallium arsenide samples of different surface roughness. And we have discussed the effect of the surface topography on the positron life.

因为正电子湮没谱测量能直接给出缺陷的信息，我们用正电子寿命谱测量不同表面粗糙度的GaAs样品，讨论了表面形貌对常规正电子寿命测量结果的影响。

In the single crystal of C60 with a FCC structure,positron mainly appears outside the C60 molecule.The main annihilation space is the interspace between molecules.The calculated positron bulk lifetime in C60 is 352ps, which agrees with experiment value of 356ps in literature.In carbon nanotube bundles with different dimeters,as the diameter of carbon nanotubes increases,the main space where positron appears changes from the interspace of carbon tubes to the space inside carbon tubes,the radio between positron annihilation with valence eletrons and core eletrons becomes larger,the positron bulk lifetime in carbon nanotube increase rapidly first and come to be a constant at the end.The calculated positron lifetime of carbon nanotube with a dimeter of 0.8～1.6ns is 332～470ps,which agrees with the experiment value of 394ps.Positron annihilation has been studied in widly used compound semiconductors.

计算结果表明：在片层结构的石墨晶体中，正电子主要在石墨层间的空隙中湮没，计算出的石墨中的正电子寿命为208 pS，与文献中的实验结果215 ps符合很好；在金刚石单晶中，正电子主要在碳原子之间的空隙中存在并发生湮没，计算出的金刚石中的正电子寿命为115 ps，文献中的实验结果110 ps左右符合；在面心立方结构的C60晶体中，正电子主要在C60分子球壳内外侧及分子之间存在，C60球形分子中心正电子分布很少，正电子的湮没区域集中在C60分子之间的空隙区域，计算出的C60中的正电子寿命为352 ps与文献中的实验结果356ps相符合；对于不同管径碳米管束中的正电子分布，随着碳纳米管直径的增加，碳纳米管束中的正电子由主要在碳纳米管管间的区域出现转变为主要在碳纳米管管内中心的区域出现：碳纳米管束中的正电子与碳原子的价电子的湮没概率变得越来越大，与核心电子的湮没概率变得越来越小；碳纳米管束中正电子的湮没寿命先迅速增大，而后趋于一定值。

We introduced two newly developed methods, one is the Maximum Entropy Principle for the analysis of the positron lifetime spectra, and another is the two-detector Doppler broadening technique with so-called W-S map for identification elemental specificity of positron annihilation spectra.

介绍了最新发展的正电子谱学方法，用于分解正电子寿命连续分布的最大熵原理，用于鉴别缺陷化学环境的双探头多普勒展宽和W-S图。

The distribution of positron wavefunction and positron annihilation rate are analyzed.

分析了不同结构的单晶中自由正电子的分布信息和湮没信息。

Positron Emission Tomography is a kind of atraumatic technology which can detect in itro the metabolic trace of emitted element in human body and can perform 3D imagings.

正电子发射断层成像技术（Positron Emission Tomography，PET）是一种通过体外测量发射性元素在人体内的代谢轨迹，并可进行三维成象的无创检测技术。

This work offers a large number of data which can be used to analyze and compare with experiment values in the future.It bulids a theory platform for the later research of elements.Positron annihilation in several carbon allotropes has been studied.The results show that:Positron mainly annihilates in the interspace between layers in the single crystal of graphite.

元素单晶中的单空位附近的束缚态正电子寿命计算时与实验结果比较一部分符合的很好，还有一部分单空位附近的束缚态正电子寿命值与实验结果比较相差较大，这可能是计算中固定了单空位的近邻原子，没有考虑单空位形成时周围原子的重新排布造成的，也可能是该方法的固有缺陷。

The new positron production linac from the electron gun to the positron source has been installed into the tunnel.

目前，正电子产生加速器，从电子枪直到正电子源，已经安装到了BEPC直线加速器隧道。

It goes back to what I told you...

现在回到我告诉过你的。。。

With a supporter in Mr Charest and an admirer in Mr Dumont, Mr Harper may be encouraged to call an election himself.

由于在沙雷那边有个支持者，杜蒙那边有个崇拜者，鼓励哈珀为自己举行一次选举。