Dresden 2006 – scientific programme

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MM: Metall- und Materialphysik

MM 42: Diffusion II

MM 42.4: Talk

Friday, March 31, 2006, 11:45–12:00, IFW B

Element Specific Defect Investigation on Mg-Alloys with Coincident Doppler Broadening Spectroscopy — •Martin Stadlbauer¹, Christoph Hugenschmidt², Klaus Schreckenbach², and Peter Böni¹ — ¹Physikdepartment E21, James-Franck-Straße, 85748 Garching — ²ZWE FRM-II, Lichtenbergstraße 1, 85748 Garching

A new coincident Doppler broadening spectrometer (CDBS) at the high intense positron source NEPOMUC [1] in Garching was set into operation. The Doppler broadening of the 511 keV annihilation line reveals not only information about the defect concentration of the sample but also the chemical surrounding at the annihilation site. Since positrons are efficiently trapped at open volume defects, it becomes feasible to identify the elements in the vicinity of these defects. For this purpose, two collinear Germanium detectors are used in coincidence in order to reduce the background efficiently. Annealed samples of Magnesium, Aluminum, Zinc and AZ31 were investigated with CDBS in order to compare the shape of the annihilation line in the high momentum region and to get reference spectra. Furthermore, ion irradiated samples of AZ31 were measured to reproduce the defect profile by quantifying the S-parameter versus sample potential between 1 and 30 keV and position. Additionally coincidence spectra were recorded in order to detect any changes in the chemical surrounding of the defects.

[1] Hugenschmidt, C., G. Kögel, R. Repper, K. Schreckenbach, P. Sperr, B. Strasser und W. Triftshäuser: NEPOMUC - The New Positron Facility at FRM II, Mat. Sci. Forum, in press, 2004