Reasons for the deviation of I1/I3 and τ1 from the expected lifetime parameters of positronium annihilation in polymers

G. Dlubek*, S. Eichler, Ch Hübner, Ch Nagel

*Corresponding author for this work
31 Citations (Scopus)


High quality positron lifetime spectra were taken for several amorphous polymers. The spectra were analysed using the routine MELT which assumes continuous lifetime distributions, as well as the discrete-term analysis routine LIFSPECFIT. Disagreements between the analysed lifetime parameters and theoretical expectations, I1/I3Ip-Ps/Io- Ps=1/3 and τ1τp-Ps, which are well known, also appear in our results. The disagreements are distinctly larger using a discrete-term routine than when applying MELT (or CONTIN). From the analysis of computer-generated spectra, we found that these disagreements may be well understood by assuming a distribution of e+ lifetimes in addition to an o-Ps lifetime distribution, both of which can occur as consequence of size and shape distributions of free-volume holes in amorphous polymers (or of bubbles in molecular liquids). The disagreements appear to be due to the inability of the routines correctly to mirror very broad lifetime distributions. For broad distributions, MELT (and also CONTIN) delivers, as an artefact of the spectrum analysis, a distribution consisting of two narrow subpeaks instead of a single broad one. The lower subpeak of the e+ lifetime distribution may mix with the p-Ps lifetime component resulting in artificially large values for τ1 and I1. That is the reason for the unphysical increase of τ1 and I1 with decreasing I3 observed in the analysed parameters of simulated as well as experimental spectra.

Original languageEnglish
JournalNuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms
Issue number4
Pages (from-to)501-513
Number of pages13
Publication statusPublished - 01.01.1999


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