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

LEED作为一种表面分析技术，在早期使用频率较高。目前，由于LEED数据的理论处理困难，RHEED得到了有效的利用。在本项目中，我们的目标是开发一种超低能正电子衍射仪，它似乎易于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具有倍数低、无交换作用、内电势几乎为零等优点。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，我们计算了正电子在各种条件下的运动轨迹，并设计了静电对接透镜系统。该聚焦透镜系统由圆柱形静电环双管透镜、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…开发的透镜系统更多的Soa。这支Soa枪在很大的范围内表现出了极好的聚焦性能。轨迹计算采用电子光学中广泛使用的变换矩阵法。分别计算了从第一个SOA胶到CMA入口处、从CMA出口到第一个重塑晶体、从第二个SOA枪到第二个重整器晶体、从第三个SOA枪到最后一个变焦透镜、从有变焦透镜存在到试件位置的轨迹。根据这一计算，我们确定了35个静电环的最佳外加电压。在这种布置下，在1.15度的散射角下，获得了1.7 mm的LEV、0.5 eV和0.17 mm的束流直径。作为对超低正电子衍射的初步测量，我们测量了由BaF_2闪烁体和光电倍增管组成的组件在铜(100)面上湮没正电子所产生的伽马射线计数率随入射正电子能量的变化。在与布拉格条件相对应的能量处，计数率显示极小值。这保证了这台仪器的高效运转。较少

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