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

为了研究聚合物的表面，需要用脉冲慢正电子束(PSPB)来确定聚合物的注入时间。通常情况下，PSPB是用直线加速器制作的，需要很大的设备。在这个项目中，使用放射性同位素建造了一个桌面尺寸的小型仪器。在直径为2 cm、长为5 cm的铝管上施加射频场，获得了聚束脉冲光束。长度由位置通过管子的飞行时间确定。因此，40 MHz的射频被用来将刚玉光束聚集成聚束光束。宽度为500到600ps，足以研究寿命大于1.5 ns到2 ns的聚合物样品。为了获得300ps宽的束流，需要另一个主聚束器。在本项目中，成功地建立了获得脉冲聚束束流的装置，并将其应用于测量聚合物：聚乙烯、环氧树脂、环氧复合材料、环氧覆膜在金属硅上的寿命。在聚乙烯中，正电子的形成随深度的增加而增加。用非破坏性方法观察了复合材料的表层。对硅片上广泛应用于集成电路和电子工业的低K薄膜进行了研究。已成功观测到正电子寿命约为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