Karl Franzens University Graz
Graz University of Technology
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Karl Franzens University Graz | Graz University of Technology | |
Positrons Probing Matter – Novel Applications of the Low‐Energy High‐Intensity Positron Beam at NEPOMUC The neutron induced positron source NEPOMUC at the FRM II provides the world’s highest intensity of 9x108 moderated positrons per second. The high positron intensity leads not only to a drastically reduced measurement time and an improved signal-to-noise ratio but also to the realization of new experiments using mono-energetic positrons. Positron beam experiments (E=0.1 - 30 keV) are presented where one benefits from the defect sensitivity and the elemental selectivity of (coincident) Doppler broadening spectroscopy of the annihilation line. Examples are spatially resolved defect maps of plastically deformed or irradiated metals, and the non-destructive investigation of layered systems. At the surface, the annihilation of low-energy positrons with core electrons initiates the emission of Auger-electrons that allows the examination of the topmost atomic layer. Recently, we succeeded to reveal the surface segregation of Cu in Pd with time dependent positron annihilation induced Auger-electron spectroscopy. Within this presentation, an overview of the NEPOMUC beam facility and the positron instrumentation is given as well. Future developments and applications of the high intensity positron beam will be discussed. |