Dresden 2026 – scientific programme

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FM: Fachverband Funktionsmaterialien

FM 19: Advanced Microscopy and Tomography for Functional Materials

FM 19.7: Talk

Thursday, March 12, 2026, 12:00–12:15, BEY/0E40

Defects in Materials: Limitations of the Trapping Model - the Influence of Corrupt Components in Positron Lifetime Spectra - cured by a New Spectrometer? — Torsten Staab, •Dominik Boras, and Danny Petschke — LCTM / IFB, Department of Chemistry, University of Wuerzburg, Roentgenring 11, D-97070 Wuerzburg, Germany

Positron lifetime spectroscopy is able to extract densities for defects (e.g. vacancies or dislocations) from the measured spectroscopic data by applying the so-called trapping model, which describes the decomposition of lifetime spectra into two or more components (lifetimes and intensities). Since the procedure of fitting several exponential decays folded by a mimicked instrumental resolution function (IRF) is a so-called ill-posed problem, the goodness of the fit relies heavily on the quality of the recorded data. By our digital twin of a positron lifetime spectrometer we could clearly see the strong influence of back scattered and corrupted coincidences on recorded spectra. Unfortunately, even by physically filtering digitised pulses, those events cannot be removed. One way to reduce their effect are changes in the geometry (90° instead of 180°) of the detector set-up leading to heavy losses in efficiency (about 90%). However, this leads to much more realistic bulk positron lifetimes of light materials (Mg, Al, Si) in accordance with calculations, and enables correct decompositions by the trapping model. We present here a new fully digitised spectrometer with an IRF described by one singe Gaussian and a FWHM of 128ps together with 22-Na sources without positronium having a single lifetime component.

Keywords: Positron Lifetime Spectroscopy; Metals; Ceramics; Polymers; Free volume