Münster 2017 – scientific programme

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HK: Fachverband Physik der Hadronen und Kerne

HK 27: Poster

HK 27.38: Poster

Tuesday, March 28, 2017, 16:45–18:45, F Foyer

Investigations of ⁵⁵Fe energy spectra in Ne-CO₂ gas mixtures for GEM detectors — •Viktor Ratza, Markus Ball, Mathias Liebtrau, and Bernhard Ketzer for the ALICE collaboration — Helmholtz-Institut für Strahlen- und Kernphysik, Universität Bonn, DE

With the planned upgrade of the ALICE Time Projection Chamber the current multi-wire proportional chambers will be replaced by a Gas Electron Multiplier (GEM) - based technology in order to allow for a continuous operation at high interaction rates up to 50 kHz. A stack of four GEM stages was chosen to achieve a suppression of the ion backflow below 1%. At the same time an energy resolution of σ/E lower than 12% has to be maintained for ⁵⁵Fe in Ne-CO₂-N₂ (90-10-5) at a total gain of 2000. This requires a reliable determination of the width of the photopeak.

Typically a simple Gaussian is fitted to the ⁵⁵Fe K_α-peak in order to determine the enery resolution. However, the obtained fit is strongly biased by the K_β-peak and an underlying background, resulting in a systematic shift of the estimated energy resolution. This effect can be of the order of one percentage point.

In order to obtain a more appropriate description of the energy spectrum the background was investigated in detail. Taking the K_β-peak and the underlying background into account a fit model was introduced to achieve a more realistic and consistent description of the energy spectrum and thus the energy resolution.

Supported by BMBF.