Speaker
Description
Quasi-elastic neutron scattering (QENS) provides atomic-scale temporal and spatial information about diffusion, rotation, and other slow dynamics in systems ranging from catalysts to energy materials to living cells. On the other hand, it is highly limited by flux, particularly when applied to small samples (e.g. proteins or other biomolecules) or weak scatterers (e.g. Li+ or Na+ motions in battery materials). The data analysis is furthermore often complicated by the coexistence of coherent and incoherent scattering in the spectra. SHERPA is a design concept for an indirect geometry time‑of‑flight spectrometer at the ISIS Neutron and Muon Source that will combine high count-rate QENS capabilities with polarization analysis, which permits the separation of the coherent and spin-incoherent components of the neutron scattering cross section. The high count rate of SHERPA is achieved through the combination of a modern double‑focusing elliptical neutron guide and a secondary spectrometer that exploits the prismatic effect of the analyzer crystals and a novel time-focusing geometry. The proposed design delivers at least an order‑of‑magnitude gain in count-rate compared with existing instruments at ISIS, alongside a moderately high energy resolution ($\Delta E=12–17\mu$eV), a flexible momentum‑transfer resolution (with $\Delta Q_{max}= 0.1–0.3$Å$^{-1}$), and a $Q$-range of $0.2<Q<2$Å$^{-1}$. Rapid changeover between the polarized and unpolarized modes is achieved by using transmission-type supermirror devices for both the polarizer and the polarization analyzer. Based on its capabilities, SHERPA promises to transform the study of the full range of systems mentioned above.