Ortho-positronium lifetime studies of free volume in polycarbonates of different structures: influence of hole size distributions

Abstract

Certain anomalies were obsd. in computer fitting of data from positron annihilations in polymers. These suggest that some reported ortho-positronium lifetimes and intensities in these polymers could be artifacts of the computer-fitting procedure. To evaluate this hypothesis, a computer simulation of exptl. data was developed, which can then be used to test the accuracy of the fitting program. The input to this simulation consists of the lifetimes and intensities of any no. of positron populations (including para-positronium and free positron decays), plus the spectrometer resoln. function, a contribution from annihilation in the positron source, and random background. The simulation uses the computer's random no. generator to make the output spectrum resemble an actual exptl. curve. The output spectrum is then used as input to the usual fitting program POSFIT, which dets. the best-fitting values of lifetime and intensity for three positron lifetime components. When the shortest lifetime, t1, was fixed at the theor. value of 120 ps, the values of the other lifetimes, t2 and t3, were very close to the values in the simulated input. [on SciFinder (R)]