Master Thesis defense by Rasmus Laurberg Hansen – Niels Bohr Institute - University of Copenhagen

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Master Thesis defense by Rasmus Laurberg Hansen

Understanding the behavior of Pyrolitic Graphite as an analyzer using measurements ans simulations

New instruments under development for inelastic neutron scattering makes use of arrays of Pyrolytic Graphite (PG) analyzers as well as the prismatic analyzer concept to simultaneously measure multiple scattering angles and energies, driving the need to understand and model spurious scattering from PG.

Measurements have been performed at the cold neutron powder diffractometer DMC at PSI of PG crystals at different temperatures to understand the phonon interactions in the crystals. With this data as basis a detailed model describing the effects measured have been developed using McStas. These effects include powder like behavior, total reflection, phonon contamination and Bragg peak widening of both Gauss and Lorentz shape due to mosaicity and uncertainty in the lattice parameters. With this model, simulations of an upgrade of the back-end of the RITA-II triple-axis-spectrometer at PSI have been performed. This upgrade called PSI-CAMEA contains arrays of high mosaicity analyzing PG crystals to measure outgoing energies in the 3.0 meV to 5.0 meV range. The simulation helps determine the need for collimation and shielding as well as determining the need for cooling the analyzers to avoid phonon contamination.