Berlin 2008 – wissenschaftliches Programm
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VA: Fachverband Vakuumphysik und Vakuumtechnik
VA 4: NEPOMUC positron source and experiments
VA 4.4: Vortrag
Montag, 25. Februar 2008, 16:20–16:40, H 0106
Improvement of the CDBS at NEPOMUC - Simulations and first measurements — •Martin Stadlbauer1,2, Christoph Hugenschmidt1,2, and Klaus Schreckenbach1,2 — 1TU München, ZWE FRM-II, Lichtenbergstr. 1, D-85748 Garching — 2TU München, Physikdepartment E21, James-Franck-Str., D-85748 Garching
Coincident Doppler broadening spectroscopy with positrons (CDBS) is a well established technique to investigate lattice defects and their chemical surrounding in solids and has been successfully implemented at the high intense positron source NEPOMUC at the research reactor FRM-II in Munich. In order to improve the existing spectrometer for measurements on materials with low positron trapping rates, it has been redesigned and improved with a cryostat for sample cooling to liquid nitrogen temperature. A recently installed brilliance enhancing remoderator facility at NEPOMUC enforced further changes at the CDBS-facility like an insulated magnetic field termination and a new lens system.
The new design of the CDBS-facility and simulations of the positron trajectories are shown and first measurements of the beam parameters at the sample position are presented. Furthermore, ion-irradiated magnesium samples have been investigated with the new CDBS-facility, since the positron trapping rate in magnesium is low and the trapping sites are shallow.