DEVELOPMENT OF ONE DIMENSIONAL ANGULAR CORRELATION OF POSITRON ANNIHILATION RADIATION MEASU REING WIDE MOMENTUM REGION FOR NON-DESTRUCTIVE INSPECTION OF NUCLEAR REACTOR PRESSURE VESSEL

由于第一代反应堆已经超过了最初设计的使用寿命，确保核反应堆的安全运行是一个紧迫的问题。反应堆压力容器（RPV）钢在中子辐照下的脆性是其中最重要的问题之一，这被认为是由RPV钢中Cu杂质（~ O）的超细沉淀引起的。由中子辐照引起的第一代的3%)。然而，由于目前的高分辨率透射电子显微镜（HR-TEM）很难观察到辐照诱导的Cu沉淀或聚集，因此对辐照诱导的Cu沉淀或聚集知之甚少。本工作的目的是研制一种新型的用于RPV钢无损检测的一维角相关正电子湮灭辐射（1D-ACAR）装置。我们的最终目标是建立一种方法，利用我们最近发现的Cu沉淀中亲和诱导的正电子约束，利用该仪器来分析其他技术难以检测到的超细Cu沉淀的形成过程和结构。为此，我们必须开发一种新的1D-ACAR装置，使我们能够以高动量分辨率（~ 1x10^<-3>mc）测量传导电子和核心电子的动量分布。因此，我们开发了一对具有高位置分辨率（~ 2mm），高计数率（宽有效面积：150 mm × 150 mm）和高时间分辨率的位置敏感伽玛射线探测器。一个探测器安装在固定支架上，另一个探测器安装在可垂直移动的支架上。下一步，构建用于低温（~ 15K）测量的样品室和样品室的支撑。最后，建立了对一对正电子湮灭伽马射线进行符合测量的电系统。我们对新的1D-ACAR设备进行了测试测量，以评估其性能。在高动量区观测到长尾，导致背景高，位置分辨率差。我们发现这是由闪烁光子在导光板表面的反射引起的。为了消除这种影响，探测器现在正在改进光导几何形状的设置和用于定时输出的放大器。少

Ensuring safe operation of nuclear power reactors is a recent urgent issue since the reactors of the first generation are going over their initially designed operating lifetimes. One of the most important problem is the embrittlement of the reactor pressure vessel (RPV) steels by neutron irradiation, which is considered to be caused by the ultrafine precipitation of Cu impurities contained in the RPV steels (〜O.3 %) of the first generation induced by neutron irradiation. However, little is known about the irradiation-induced Cu precipitates or aggregations because it is very difficult to observe them even by current high-resolution transmission electron microscopes (HR-TEM). The aim of this work is to develop a new type of one-dimensional angular correlation of positron annihilation radiation (1D-ACAR) apparatus for non-destructive inspection of the RPV steels. Our final goal is to establish the method, using the apparatus, to analyze the formation process and the structure of the ultr … More afine Cu precipitates, difficult to detect by other techniques, utilizing affinity-induced positron confinement in the Cu precipitate which we have recently found.For the above purpose, we have to develop a new 1D-ACAR apparatus which enables us to measure the momentum distribution of not only conduction electrons but also core electrons with high momentum resolution (〜1x10^<-3>mc). Thus, we developed a pair of position sensitive gamma-ray detectors with high position resolution (〜2 mm), high counting rate (wide effective area : 150 mm x 150 mm) and high time resolution. One detector was mounted on a fixed support, and the other detector was mounted on a support movable vertically. In the next step, the sample chamber for low temperature (〜15K) measurements and the support for the chamber were constructed. Finally, the electric system for the coincidence measurement of a pair of positron annihilation gamma-rays was set up.We performed a test measurement of the new 1D-ACAR apparatus for the evaluation of the performance. A long tail in the high momentum region was observed, which results in high background and poor position resolution. We found that this was caused by the reflection of the scintillation photons at the light-guide surfaces. To remove this effect, the detectors are now improving the setting of the light-guide geometry and the amplifiers for the timing outputs. Less