ANNIHILATION RESPONSE OF THE ORTHO - POSITRONIUM PROBE FROM POSITRON ANNIHILATION LIFETIME SPECTROSCOPY AND ITS RELATIONSHIPS TO THE FREE VOLUME AND DYNAMICS OF GLASS - FORMING SYSTEMS

摘要

Positron annihilation lifetime spectroscopy (PALS) becomes gradually a standard technique for detecting the local regions of reduced electron density of condensed systems via the formation and annihilation behaviour of ortho - positronium (o-Ps). First we give a short overview of the free volume concept and the principles of PALS method. Then, we present typical o-Ps annihilation responses of organic small molecular and simple polymer systems and their operational classification with a discussion of the microscopic origin of the distinct features between the Type I and Type Ⅱ glass formers. Further, we give a free volume interpretation of o-Ps annihilation behavior by means of two model dependent treatments of the annihilation parameters, i.e., the o-Ps lifetime, τ_3, and the relative o-Ps intensity, I_3, in terms of free volume hole size, R_h, or free volume hole fraction, f_h, respectively. Finally, an example of correlation between effective free volume hole characteristics and macroscopic dynamics will be demonstrated on the case of dielectric relaxation data of glycerol.