正电子慢化体的研究和进展

正电子湮没技术是一种研究材料的微观缺陷和相变的灵敏工具，在通常的正电子谱仪中，正电子能量为MeV量级，在样品中注入深度比较学（－100μm），主要研究材料体内的平均缺陷密度，慢正电子束方法把正电子的能量降低为keV量级（而且可以调节），注入比较浅（－μm），所以是研究表面缺陷的探测手段，正电子慢化体是产生慢正电子的关键设备，对其研究有重要意义，文章综述了慢化体研究的历史和现状，从物理概念出发介绍使正电子慢化的四种可能方法和当今慢化体的五种几何排列方法，其中应用最广泛的是钨慢化体和百叶窗式的排列方式，效率最高的是惰性气体固体慢化体，而加电场慢化体是有待开发的高效慢化体。

THE GENERATION AND DEVELOPMENT OF THE MODERATORS FOR SLOW POSITRON BEAM

The positron annihilation technique is a sensitive tool for studying microdefects and phase transitions in various materials.Usually the energy of positrons is on the order of MeV and the implantation depth about 100 microns,so the bulk average defect density can be studied.In a slow positron beam the positron energy is about keV and the implantation depth a few microns,so surface defects can be detected.Positron moderator is the key device for obtaining a slow positron beam.We review the history and development of the positron moderator,including four methods that convert fast positrons into slow mono-energetic positrons and five array types.The tungsten moderator is the most widely used one while the inert gas solid moderator is the most efficient.Field-enhanced moderators with their high efficiency have great potential but need to be developed.The vane arrangement is the most commonly found.