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MM: Fachverband Metall- und Materialphysik

MM 9: Poster

MM 9.67: Poster

Montag, 17. März 2025, 18:30–20:30, P1

Upgrading the Coincidence Doppler Broadening Spectrometer at FRM II — •Danny R Russell, Francesco Guatieri, Leon Chryssos, and Christoph Hugenschmidt — FRM II - Technische Universität München, München, DE

The coincidence Doppler broadening spectrometer (CDBS) at the Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II) provides state-of-the-art, depth dependent detection of defects and chemical composition at the annihilation site. A monoenergetic positron microbeam (50 µm FWHM) is guided onto a sample where positrons annihilate with electrons. The Doppler broadening of the characteristic 511 keV annihilation peak is measured by observing both emitted photons simultaneously.

We present simulations and hardware design for an upgrade to the CDBS which will allow backscattered positron capture. Up to ∼ 40 % of the incident positrons are backscattered when they reach the sample surface. The annihilation events occurring when these backscattered positrons return to the sample or annihilate in experimental hardware contribute unwanted signal to the measured spectrum which cannot be removed in data processing.

We use an in-house particle tracking code to design a positron dump that will capture backscattered positrons at an electrode outside detector lines of sight. This will reduce the unwanted signal by up to 50 % and improve the quality of CDBS data. Additionally, we apply the same code to optimize an electrostatic focusing lens, further increasing the spatial resolution of the instrument.

Keywords: Positron; Beam; Experimental Techniques