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

传统的正电子光谱学方法存在一定的局限性。例如，除了非常有限的情况，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灭作为一种无损检测技术来评价材料的实际困难。解决上述限制的最基本方法是将正电子源与样品分离，以便在样品可以暴露于任何极端条件下而没有放射性污染风险的情况下，始终将正电子源保持在温和的环境中。另一方面，由于停止探测器探测到的0.511MeV光子与开始探测器探测到的1.28MeV光子来自同一个正电子，因此停止探测器探测到的1.22 >Na正电子源在正电子发射后发射的1.28MeV光子不能再作为寿命测量的起始信号。…More β^+>-γ符合技术，其中开始信号由通过开始检测器的正电子给出，非常适合分离源/样品几何。为了扩大正电子湮灭的应用领域，研制了一种新的β^<+>-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，而不是传统的配备快速闪烁体的光电倍增管，这是实现便携式正电子寿命光谱仪的一步，可以对材料进行现场无损评估。另一方面，用于正电子能量选择的电磁透镜现在允许使用台式正电子寿命谱仪在高温下进行原位测量。改进了正电子湮没光谱仪的设计，扩大了正电子湮没在现场高温测量和材料现场无损评价中的适用性。在高温下，许多重要或潜在材料的缺陷及其性质将得到澄清。这些信息将对开发材料及其加工非常有用。另一方面，装有小型正电子传感器的便携式材料无损检测仪即将问世。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