Breakthrough in neutron backscattering spectroscopy: Energy resolution improved by one order of magnitude using the GaAs 200 reflection.

We have developed and tested a demonstrator for a neutron backscattering spectrometer with a tenfold enhanced energy resolution. This is made possible by taking advantage of the narrow intrinsic linewidth of the GaAs 200 Bragg reflection, which is one order of magnitude smaller than the linewidth of the currently used Si 111. First measurements yielded an unprecedented energy resolution of 78 neV FWHM, a factor of 10 narrower than the standard Si 111 configuration and about a factor of 4 smaller than the highest energy resolution currently available with Si 111. These measurements provide proof of concept for the construction of a full-scale user instrument.