Inelastic nuclear resonant scattering with sub-meV energy resolution

With an undulator-based synchrotron source and a tunable x-ray monochromator, we produce an x-ray beam with a flux of 4×108 photons/s in an energy bandwidth of 920±110 μeV (ΔE/E≈6.2×10−8) at a photon energy of 14.4 keV. The tunability of the monochromator allows for a measurement of lattice excitations in α-Fe using the technique of inelastic nuclear resonant scattering from Fe57. The phonon density-of-states are extracted from the measurement and compared to the calculated phonon density-of-states derived from neutron-scattering measurements.