Analysis of positron annihilation lifetime data presented as a sum of convoluted exponentials with the program “SPLMOD”

Abstract

The reliability of a least squares analysis of positron annihilation lifetime data represented as a sum of convoluted exponentials is investigated with computer-stimulated test data. The method of analysis, which is available as a computer program called “SPLMOD” [R.H. Vogel, Technical Report EMBL-DA08, European Molecular Biology Laboratory, Heidelberg, FRG, (1986)], avoids direct determination of the instrument resolution function by employing the decay curve of a reference material with a well-known single lifetime. The performance of the algorithm for extracting positron annihilation lifetime information was evaluated by using several measures of the information content of the decay curve described recently by Schrader and Usmar [in: Positron Annihilation Studies of Fluids, ed. S. Sharma (World Scientific, Singapore, 1988)]. The sensitivity of the algorithm to systematic errors including errors in the resolution function, shifts in the zero time channel and contamination of the reference decay curves by additional lifetime components was evaluated. The method provides excellent estimates of lifetime parameters when the reference decay curve accurately reflects the resolution function of the sample data. However, the algorithm is extremely sensitive to errors in the instrument resolution function.