Untersuchungen zur Verbesserung der Energieaufl\"osung f\"ur Neutronenr\"uckstreuspektrometer unter Verwendung von Idealkristallen mit geringer dynamischer Breite der Reflexionskurve

TL;DR

This paper investigates methods to enhance the energy resolution of neutron backscattering spectrometers by utilizing ideal crystals with low dynamic width of the reflection curve, combining theoretical analysis and experimental validation.

Contribution

It introduces a new approach using GaAs-200 reflection crystals to improve energy resolution, achieving a measured line width of 43 neV, closer to the theoretical limit.

Findings

Theoretically limited energy resolution of 13 neV for GaAs-200 reflection.

Experimental setup achieved a line width of 43 neV.

Identified key error sources affecting resolution, such as temperature and vibrations.

Abstract

The thesis 'Investigations to Improve Energy Resolution for Neutron Backscattering Spectrometers Using Ideal Crystals with Low Dynamic Width of the Reflection Curve' first introduces the concept of the neutron backscattering spectrometer and their scanning methods by Doppler variation of the neutron energy on a moving Bragg-reflecting crystal. It further reveals the foundations of the dynamical theory of diffraction, with concepts on dispersion surfaces describing total reflection, refraction, and Laue-Bragg diffraction. The natural line width of a reflecting crystal is given by the structure factor, which limits the energy resolution of a Si-111 monochromator to a minimal 300 neV. The present project is to investigate the energy resolution of the GaAs-200 reflection, theoretically limited to 13 neV. An experimental setup is presented encompassing optics, mechanics, and detector electronics, and an experimental line width of 43 neV has been obtained. The value is discussed with error sources such as temperature stability, vibrations, misalignment, and crystal defects.