Construction of a non-destructive evaluation system of materials in use by using positrons

传统的正电子能谱法存在一定的局限性。例如，除了非常有限的情况外，在高温下原位正电子寿命测量几乎是不可能的。另一个缺点是使用正电子湮没作为无损检测技术来评估材料的实际困难。解决上述限制的最基本方法是将正电子源与样品分离，以便使源始终处于温和的环境中，而样品可以暴露在任何极端条件下，而没有放射性污染的风险。另一方面，在<22>正电子发射之后从_ Na正电子源发射的1.28MeV光子不能再用作寿命测量的开始信号，因为难以确保由停止探测器探测到的0.511MeV光子源自由开始探测器探测到的发射1.28MeV光子的相同正电子。的 关于我们 β^+&gt;-γ符合正电子湮没技术是一种利用正电子通过起始探测器产生起始信号的技术，适用于源/样品分离的几何结构。为了拓展正电子湮没技术的应用领域，研制了一台新的β^&lt;+&gt;-γ符合正电子寿命谱仪。采用硅雪崩二极管作为启动探测器，而不是传统的光电倍增管配备了快速闪烁体已被尝试作为一个步骤更接近实现的便携式正电子寿命谱仪，使现场无损评价材料。另一方面，正电子能量选择的电磁透镜的加入，现在允许在高温下的原位测量与台式正电子寿命spectrometer.Improved设计的正电子湮没spectrometers扩展的适用性，正电子湮没原位高温测量和现场无损评价材料。许多重要或潜在的材料在高温下的缺陷及其性质将得到澄清。这些信息对于材料的开发和加工将是非常有用的。另一方面，带有小型正电子传感器的便携式材料无损检测仪也将很快出现。少

Conventional positron spectroscopy methods suffered from certain limitations. For example, in-situ positron lifetime measurement is almost impossible at high temperature except for very limited cases. Another shortcoming is the practical difficulty to use positron annihilation as a nondestructive testing technique for the evaluation of materials.The most essential method to resolve the limitations mentioned above is to separate the positron source from the specimen in order to keep the source in a mild environment at all times while the sample can be exposed, to any extreme conditions with no risk of radioactive contamination. On the other hand, the 1.28MeV photon which is emitted from _<22>Na positron source just after a positron emission, can no longer be used as the start signal for the lifetime measurement as it is hard to assure that a 0.511MeV photon detected by the stop detector originated from the same positron that emitted the 1.28MeV photon detected by the start detector. The … More β^+>-γ coincidence technique, in which the start signal is given by a positron that has passed through the start detector, is well-suited to separate source/sample geometry.A new β^<+>-γ coincidence positron-lifetime spectrometer has been developed in order to expand the field of applications of positron annihilation. The adoption of a silicon avalanche diode as the start detector instead of a conventional photomultiplier tube equipped with a fast scintillator has been attempted as a step closer to the realization of a portable positron-lifetime spectrometer enabling on-site nondestructive evaluations of materials. On the other hand, the incorporation of an electromagnetic lens for positron-energy selection now allows for in-situ measurement at high temperatures with a desk-top positron lifetime spectrometer.Improved designs of positron annihilation spectrometers extend the applicability of positron annihilation to in-situ high temperature measurement and to on-site nondestructive evaluation of materials. Defects and their properties will be clarified in many important or potential materials at high temperatures. Such information will be quite useful to develop materials and their processing. On the other hand, portable nondestructive tester of materials with a small positron sensor will soon appear. Less