Neutron Sciences Directorate

BASIS is a near-backscattering, crystal-analyzer spectrometer that provides very fine energy resolution, as low as 3.0 to 3.5µeV at the elastic peak (depending on sample size). This requires a long initial guide section of 84 m from moderator to sample in order to achieve the timing resolution necessary for obtaining the desired energy resolution. BASIS provides an excellent dynamic range near the elastic peak of about plus and minus 100 µeV in the standard high-intensity operation regime, which, if needed, could be extended to plus and minus 200 µeV and beyond. The spectrometer is optimized for quasielastic scattering but provides about 0.1% resolution in energy transfers up to ~40 meV; the inelastic excitations need to be very sharp in order to be measurable at high energy transfers.

For detailed information about BASIS, please refer to "A time-of-flight backscattering spectrometer at the Spallation Neutron Source, BASIS" Mamontov, E., and Herwig, K. W., Review of Scientific Instruments 82, 85109 (2011).