Interpretation of positron lifetime spectra arising from micellar solutions. Determination of the ortho-positronium diffusion coefficient in the solvent

Sz Vass, Zs Kajcsos

Research output: Contribution to journalArticle

Abstract

Positron lifetime spectra arising from micellar solutions of sodium dodecylsulphate (SDS) are interpreted in terms of a classical positronium diffusion model published earlier. Unlike the generally accepted assumptions, this model results in a non-exponential ortho-positronium (o-Ps) lifetime density function. A new method is presented for the simultaneous fitting of this lifetime density function to independent lifetime spectra recorded under the same experimental conditions. Among the fit parameters Dp, the diffusion coefficient of o-Ps in the solvent (i.e. heavy water) phase is studied in detail; a detailed error analysis for Dp is also given. Provided that the mean aggregation number of SDS micelles is about 60, the published Dp values show that the diffusion coefficient of o-Ps in (heavy) water at room temperature is lower than that of small ions and molecules and the Arrhenius plot indicates a strong o-Ps localization in the solvent. The hydrodynamic radius of o-Ps is calculated from the o-Ps and micellar diffusion coefficients and from the micellar radius; it is greater than that of small ions and molecules and this can be considered as an independent indirect proof for the existence of o-Ps bubble in the (heavy) water.

Original languageEnglish
Pages (from-to)403-416
Number of pages14
JournalInternational Journal of Radiation Applications and Instrumentation. Part
Volume32
Issue number3
DOIs
Publication statusPublished - 1988

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