Regensburg 2025 – scientific programme

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KFM: Fachverband Kristalline Festkörper und deren Mikrostruktur

KFM 5: Instrumentation, Microscopy and Tomography with X-ray Photons, Electrons, Ions and Positrons

KFM 5.4: Talk

Monday, March 17, 2025, 15:45–16:00, H9

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

Since the early days of positron lifetime spectroscopy, the meaningful decomposition of lifetime spectra into two or more components has been highly disputed. This procedure is extremely important to extract correct defect densities. Since the procedure of fitting several exponential decays folded by a mimicked instrumental resolution function to extract positron lifetimes and intensities is an "ill-posed problem", the goodness of the fit relies heavily on the quality of the recorded data. In the past there have been several simulation attempts to create and decompose spectra into two or three components (lifetimes and intensities). However, those attempts always assumed "ideal", random number Monte Carlo simulated data. Hence, the following data analysis has been fairly straight forward. By our recently developed digital twin of a positron lifetime spectrometer we could clearly see the strong influence of back scattered and corrupted coincidences on the lifetime spectrum. Unfortunately, those events cannot be removed by physically filtering digitised pulses. Changes in the geometry of the set-up lead to much more realistic bulk positron lifetimes of light materials (Mg, Al, Si) in accordance with calculations and correct decompositions in accordance with the trapping model, while the efficiency is reduced by 95%.

Keywords: Trapping Model; Positron Annihilation; Lifetime Spectroscopy