Berlin 2018 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 74: Structural Materials (Steels, light-weight materials, high-temperature materials)

MM 74.4: Talk

Friday, March 16, 2018, 12:00–12:15, H 0106

Defect Imaging Using the Positron-Microbeam of the CDB Spectrometer at NEPOMUC — •Thomas Gigl, Lukas Beddrich, Marcel Dickmann, Benjamin Rienäcker, Mathias Thalmayr, Sebastian Vohburger, and Christoph Hugenschmidt — Heinz Maier-Leibnitz Zentrum (MLZ) and Physik Department E21, Technische Universität München, Lichtenbergstr. 1, 85748 Garching, Germany

The Coincidence Doppler Broadening Spectrometer (CDBS) at the positron beam facility NEPOMUC was upgraded with a beam brightness enhancement system in order to enable CDB spectroscopy with improved spatial resolution. The positron is transported in a newly designed µ-metal shielded optically column comprising several electrostatic lenses, magnetic compensation coils, and beam monitors. The new brightness enhancing device is integrated in the electrostatic beam guiding system and basically comprises a beam focusing unit and a Ni(100) foil of 100 nm thickness working as transmission remoderator. For high resolution measurements the positron beam is first focused onto the Ni remoderation foil before it is accelerated up to 25 keV onto the sample. In order to estimate the beam diameter at the sample position spatially resolved DB measurements have been performed. Without remoderator a lateral resolution of 200 µm is obtained. Using the brightness enhancement system the beam spot could be reduced to 33 µm. Benefiting from the improved resolution of the CDBS upgrade, defect spectroscopy on various light metal alloys has been performed recently.