Keywords: 
• 慢化体 /
• 慢正电子束

Abstract: 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.