Gallium arsenide for high resolution in neutron backscattering spectroscopy

The usage of gallium arsenide instead of silicon crystals is a great step forward in neutron backscattering spectroscopy. The theoretical energy resolution limit for an ideal GaAs(200) crystal is just 13 neV, since it scatters neutrons much less than silicon. It’s been known since the 1990s that the reflection off the (200) surface of galliumarsenide could potentially do better, but only now the GaAs fabrication is sufficiently advanced for a large-area perfectly crystalline analyzer to be feasible. Many paramters have to be taken into account and optimized in the application as analyser. Berhard Frick, Andreas Magerl and their colleagues have tackled the issue and done first proof-of-concept measurements at a prototype at IN16B, ILL. They arready reach a resolution of 78 neV - the lowest one for silicon lies at 300 neV. Johanna L. Miller reports on the project and its potential for neutron backscattering spectroscopy in Physics Today (72). (original publication: K. Kuhlmann, M. Appel, B. Frick, and A. Magerl, Rev Sci Instrum 90, 015119 (2019)) The project was funded by the joint research program of the BMBF. [more]