正电子

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。

Positron Lifetime experiments were performed in plastically deformed and undeformed Zn-doped p-type GaAs to investigate deformation-induced point defects.

在n型和SI型InP中，V〓和V〓均捕获正电子，但在p型InP中，正电子只探测到了V〓。

Positron emission tomography is a kind of atraumatic technology which can detect in vitro 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是一种利用向生物体内部注入正电子同位素标记的化合物而在体外测量它们的空间分布和时间特性的三维成像无创检测技术。

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。

In positron emission tomography , or PET, a patient ingests or is injected with a slightly radioactive substance that emits positrons, which can be monitored as the substance moves through the body.

在正电子发射X射线摄影技术中，病人要咽下或被注射一些有少许放射性的物质来发出正电子。当这些物质在人体内运动时，正电子可被监测到。

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 has been found that the microhardness HV and the mean positron lifetimeexhibit quasi-periodical oscillation when the number of the fatigue cycles is increased.

通过对不同循环次数的热疲劳样品的正电子寿命谱和表面显微硬度的测量，发现表面显微硬度HV和平均正电子寿命τ随疲劳循环次数N的变化呈现出类周期振荡特征。

It was found that the spectra contained two intense components and a weak one; the long lived component corresponds to the positronium.

配合时域介电谱方法用正电子湮没技术对硫酸三甘肽的铁电相变过程进行了测量，发现正电子寿命谱有两个较强的成份和一个很弱的成份，后者相应于正电子偶素，各分量在相变点附近很窄的温区出现奇异性质，对其起因作了解

Breath, muscle contraction of the buttocks; arch body, as far as possible to hold his head, right leg straight towards the ceiling (peg-leg knee in order to avoid muscle tension).

呼气，收缩臀部肌肉；拱起身体，尽量抬起头来，右腿伸直朝向天花板（膝微屈，以避免肌肉紧张）。

The cost of moving grain food products was unchanged from May, but year over year are up 8%.

粮食产品的运输费用与5月份相比没有变化，但却比去年同期高8％。