Do MELT or CONTIN Programs Accurately Reveal the o-Ps Lifetime Distribution in Polymers? Analysis of Simulated Lifetime Spectra

Simulated positron lifetime spectra consisting of three components, among them a Gaussian o-Ps lifetime distribution of different width σ3, were extensively analysed using the MELT and CONTIN routines. Conclusions were reached on the relevance of the shape and width of the analysed o-Ps lifetime distributions as a function of simulated standard deviation σ3 (0 to 500 ps), the total number of counts (1 M, 10 M, 50 M), and the regularization (entropy weight). Furthermore, the ability of the techniques to distinguish broad distributions from (discrete) neighbour lifetimes, and to resolve close neighbour lifetimes was investigated. The behaviour of the characteristic lifetimes τi and intensities li of the three spectrum components was studied and compared with results coming from the discrete-term analysis. The results of the study lead to a critical view on the current use of the routines in estimating o-Ps lifetime distributions and from these the free-volume hole size distributions in polymers.