Dresden 2014 – wissenschaftliches Programm

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MI: Fachverband Mikrosonden

MI 1: Festkörpercharakterisierung mit Positronen

MI 1.3: Tutorium

Sonntag, 30. März 2014, 17:30–18:15, HSZ 201

Positron annihilation studies at an electron accelerator: From thin films to bulk samples and 3-D imaging — •Andreas Wagner — Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstr. 400, 01328 Dresden, Germany

Positron annihilation lifetime spectroscopy serves as a perfect tool for studies of open-volume defects in solid materials such as vacancies, vacancy agglomerates, and dislocations. Moreover, structures in porous media can be investigated ranging from 0.3 nm to 30 nm employing the variation of the positronium lifetime with the pore size. While lifetime measurements close to the material's surface can be performed at positron-beam installations, bulk materials, fluids, gases, bio-materials or composite structures cannot or only destructively accessed by positron beams. In the tutorial, a set of new installations at the superconducting electron linear accelerator ELBE will be discussed. Key to all experiments is the timing resolution and the variability in pulse repetition rate which enables new ways of materials research with positrons. Depth dependent defect studies (both annihilation lifetime and Doppler-broadening) on thin films are enabled by a tunable monoenergetic positron beam. Experiments using high-energy electron-bremsstrahlung as a source for pair production inside the investigated samples release vacuum constraints and allow studying structural defects on the atomic scale even for radioactive samples with significant intrinsic activities. Some recent examples and results will be given and a facility extension for in-situ defect generation studies will be presented.