A Pulsed Slow Positron Beam Apparatus and its Application to Thin Polymer Films

为了研究聚合物的表面，需要脉冲慢正电子束（PSPB）来确定所研究聚合物中的注入时间。PSPB一般采用直线加速器制造，需要较大的设备。在这个项目中，使用放射性同位素建造了一个桌面大小的小型仪器。采用射频法，在直径为2cm、长度为5cm的铝管上施加射频场，得到束状脉冲光束。长度由位置通过管道的飞行时间决定。因此，40兆赫的射频被用来束成束束的轮辐波束。宽度为500 - 600ps，足以研究寿命超过1.5 - 2ns的聚合物样品。为了获得300磅宽的波束，需要另一个主聚束器。在这个项目中，获得脉冲和束束光束的装置已经成功建立，并应用于测量聚合物的寿命：聚乙烯，环氧树脂，环氧复合材料，硅金属上的环氧涂层薄膜。在此应用中，得到了环氧树脂的表面热膨胀系数和体积。在聚乙烯中，正电子离子的形成随深度的增加而增加。采用非破坏性方法对复合材料的表皮层进行了观察。研究了广泛应用于1C和电气工业的硅基低钾薄膜。已成功地观察到正电子寿命约为50 ns的大空穴

In order to study the surface of polymers, a pulsed slow positron beam (PSPB) is necessary to determine the injection time in the investigated polymer. Commonly PSPB is made using a linear accelerator, which need large facility. In this project, a small apparatus desk-top size has been built using radio isotopes. The bunched and pulsing beam was obtained by the RF method, in which RF field is applied on a Al tube with 2cm diameter and 5cm length. The length is determined by the flight time of positions through the tube. Thus 40 MHz RF is used to bunch the rundum beam to a bunched beam. The width is 500 to 600ps, which is enough to study polymer samples, which have lifetimes longer than 1.5ns to 2 ns. In order to get a beam with 300pswidth, it is required another main buncher.In this project, the apparatus to obtain a pulsed and bunched beam has been successfully built and applied to measure lifetimes of polymers : polyethylene, epoxy resin, epoxy composite, epoxy coated films on a Silicon metal.In this application, the heat expansion coefficient of the surface and the bulk of epoxy resin was obtained. The increase in the positronium formation with increasing the depth was observed in polyethylene. The skin layer of the composite materials was observed by a non destructive method. Low K films on Silicon plate, which are extensively used in 1C and electric industry has been studied. Large holes with about 50 ns positron lifetime hasbeen successfully observed