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MI: Fachverband Mikrosonden

MI 9: Positron Annihilation Studies of Condensed Matter

MI 9.3: Vortrag

Mittwoch, 18. März 2015, 12:45–13:00, EMH 225

Energy modulation of a pulsed positron beam for depth dependent measurements — •Niklas Grill¹, Marcel Dickmann², Christian Piochacz¹, Sebastian Vohburger¹, and Christoph Hugenschmidt¹ — ¹Heinz Maier-Leibnitz Zentrum (MLZ) and Physik Department E21, Technische Universität München, Lichtenbergstr. 1, 85748 Garching, Germany — ²Institut für Angewandte Physik und Messtechnik LRT2, Fakultät für Luft- und Raumfahrttechnik, Werner-Heisenberg-Weg 39, 85577 Neubiberg, Germany

A two-stage bunching unit is used to generate a pulsed positron beam with a frequency of 5 MHz from a continuous beam generated by a ²²Na β⁺ source. At the first stage a sawtooth-shaped signal is used to compress a large amount of the continuous beam into pulses which are short enough for the following main buncher. This utilizes a sinusoidal function at 20 MHz to ensure a high energy modulation and thus narrow pulses. Via time-dependent electromagnetic fields the potential energy of the bunches is then raised to several keV without altering the velocity of the positrons. Subsequently the positrons can be accelerated towards ground potential, thus allowing a depth resolved measurement of samples at ground potential. This is e.g. necessary for positron re-emission experiments and Positron Annihilation Auger Electron Spectroscopy measurements performed at the NEPOMUC positron beam facility. Due to the low pulsing frequency the setup can also be used to investigate materials with long positron lifetimes, thus enabling non-destructive measurements on e.g. polymers. Within this contribution, details of the setup and first lifetime measurements will be presented.