The Trial Manufacture of a Ultra-low Energy Positron Diffraction Apparatus

LEED作为一种表面分析技术，在早期被广泛使用。目前，由于LEED数据在理论处理上的困难，使得LEED得到了有效的应用。在本项目中，我们的目标是开发一种超低能量的正电子衍射仪，它似乎很容易从理论方面进行处理，并且比LEED对表面结构更敏感。与LEED相比，ULEPD在以下方面具有优势：低多重散射，无交换相互作用，内电位几乎为零等特点。在本项目中，我们试制了一台超低能正电子衍射仪。在初始阶段，我们计算了各种条件下正电子的运动轨迹，并设计了静电透镜系统。该聚焦透镜系统由带圆柱形静电环的双管透镜、对称Einzel透镜和反对称Einzel透镜组成。对于正电子的提取，我们使用了…More Soa开发的透镜系统。这支索阿枪在很宽的范围内表现出极佳的聚焦性能。利用电子光学中广泛应用的变换矩阵法进行轨迹计算。我们分别计算了从第一个Soa胶到CMA入口、从CMA出口到第一个还原晶体、从第二个Soa枪到第二个还原晶体、第三个Soa枪到最后一个变焦透镜以及从变焦透镜的存在到试样位置的轨迹。通过计算，我们确定了35个静电环的最佳施加电压值。在这种布置下，分散角为1.15°时，光束在lev时直径为1.7mm，在10eV时直径为0.5mm，在100V时直径为0.17mm。作为超低正电子衍射的初步测量，我们用BaF2闪烁体和光电倍增管组合测量了Cu（100）表面正电子湮灭的伽马射线计数率与入射正电子能量的函数关系。计数率在与布拉格条件对应的能量处显示最小值。这保证了这台仪器的有效运行。少

As surface analysis technique, LEED was frequently used at an early stage. At present, RHEED is efficiently used because og the difficulty in the theoretical treatment of LEED data. In the present ptoject, We aimed to develop a ultra-low energy positron diffraction apparatus, which seems to be easily treated by theoretical aspects and be more sensitive to surface strcutures than LEED. As compared with LEED, ULEPD is superior in the following points; low multiple scatteting, no exchange interaction, nearly zero inner potential and so on. In this project, we manufactured trially a ulta-low energy positron diffraction apparatus. At an initial stage, we calculated the trajectory of positrons for various conditions and designed electrostatic docussing lens system. This focussing lens system was composed of two-tube lenses with cylindtrical electrostatic rings, symmetric Einzel lenses and anti-symmetric Einzel lenses. For the extraction of positrons, we utilized the lens system developed by … More Soa. This Soa gun showed an excellent focussing property in a very wide range. Trajectory calculations were made by the method of transformation matrices which is widely used in the electron optics. We calculated trajectories from the first Soa gum to the entrance to CMA, from the exit fo CMA to the first remoderatoe crystal, from the secong Soa gun to the second remoderator crystal, the third Soa gun to the final zoom lens, and from the exist of zoom lens to teh specimen position, respectively. From this calculation, we determined the optimum values of applied voltages for 35 electrostatic rings. For this arrangement, the beam diameter of 1.7mm at lev, 0.5mm at 10eV and 0.17mm at 100V was obtained at the dispersed angle og 1.15 degree. as a preliminaly measurement of ultra-low positron diffraction, we measured the counting rate of gamma rays from annihilation of positrons in the Cu (100) surface by an assembly of BaF2 scintillator and a photomultiplier tube as a function of incident positron energy. The counting rate showed minima at energies correpsonding to Bragg conditions. This garanteed the efficient operation of this apparatus. Less