Monte Carlo calculations of hole size distributions: simulation of positron annihilation spectroscopy

Consequences were explored of a hole size distribution in an amorphous polymer for the ortho-positronium (o-Ps) lifetime (t3) and intensity (I3), detd. by positron annihilation lifetime spectroscopy. The disordered lattice model, with a vacancy fraction h as a central quantity, was used to represent the equation -of-state behavior of the polymer. By means of Monte Carlo simulations, the cluster size distribution was obtained as a function of h and hence temp. The predicted av. cluster size and the cluster concn. were compared to t3 and I3 data, resp., for bisphenol A polycarbonate. Furthermore, the influence of an o-Ps lifetime distribution on the exptl. mean t3 was investigated. By mimicking the computational methods used in exptl. anal., agreement between expt. and theory in respect to t3 and to I3 in the melt ensued. In the glass, however, the exptl. I3 became increasingly smaller with decreasing temp. than was computed. These deviations might result from a distortion of the equil. free vol. [on SciFinder (R)]