The NIST high-flux backscattering spectrometer

The neutron-backscattering technique extends the dynamic range of neutron time-of-flight and conventional triple-axis spectrometers down to μeV energies and is ideal for the study of slow motions in complex liquids, jump diffusion, and quantum rotational tunneling. We report on the performance of the new high-flux backscattering spectrometer (HFBS) at the NIST Center for Neutron Research. Compared to other backscattering spectrometers, the HFBS achieves a higher neutron intensity through the use of a device called a phase space transformation chopper and a large analyzer array. A custom-designed Doppler drive for the monochromator provides a triangular velocity profile capable of high-frequency operation, thus extending the dynamic range of the spectrometer by more than a factor of two over similar instruments.