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

传统的正电子能谱方法存在一定的局限性。例如，除了非常有限的情况外，在高温下原位测量正电子寿命几乎是不可能的。另一个缺点是将正电子湮没作为一种无损检测技术用于材料评估的实际困难。解决上述限制的最基本的方法是将正电子源与样品分开，以便使源始终保持在温和的环境中，而样品可能暴露在任何极端条件下，没有放射性污染的风险。另一方面，正电子发射后发射的1.28 MeV光子不能再用作寿命测量的启动信号，因为很难保证STOP探测器探测到的0.511 MeV光子来自发射START探测器探测到的1.28 MeV光子的同一正电子。The…为了扩大正电子湮没的应用领域，我们研制了一种新型的β^+&γ符合正电子寿命谱仪。β^+-γ符合技术是由一个穿过起始探测器的正电子给出的启动信号，非常适合于源/样品的分离。采用硅雪崩二极管作为启动探测器，取代传统的配备快闪烁体的光电倍增管，是实现便携式正电子寿命能谱仪的又一步，能够对材料进行现场无损评估。另一方面，利用电磁透镜选择正电子能量，现在可以用台式正电子寿命能谱仪在高温下进行现场测量。改进的正电子湮没能谱仪的设计将正电子湮没技术的适用性扩展到了现场高温测量和材料的现场无损评估。在高温下，许多重要的或潜在的材料中的缺陷及其性质将被阐明。这些信息将对开发材料及其加工非常有用。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即将出现。较少

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