Four-reflection “nested” meV-monochromators for 20–30 keV synchrotron radiation

We present the design and performance of three silicon high-resolution ( E / Δ E ≈ 2 – 5 × 10 7 ) monochromators for synchrotron radiation that work at energies corresponding to nuclear excited states in 151Eu (21 542 eV), 119Sn (23 880 eV), and 161Dy (25 651 eV). The design of each monochromator is quite similar with the exception of the silicon crystal reflections that are used and the surface asymmetry angles that are chosen. We give the basic design underlying all three monochromators along with a table of the specific parameters used for each one. Performance in terms of resolution and spectral efficiency are measured and compared to theoretical expectations. Measurements of lattice excitations in different solids containing the aforementioned isotopes demonstrate the utility of each monochromator. Possible improvements to performance are presented.