Rayleigh scattering of synchrotron Moessbauer radiation using a variable bandwidth nuclear Bragg monochromator

By combining a variable bandwidth nuclear Bragg monochromator and a nuclear resonant reference absorber, a spectroscopic method using Rayleigh scattering of synchrotron Moessbauer radiation has been successfully developed. The nuclear Bragg monochromator filters single-line ⁵⁷Fe-Moessbauer radiation with variable energy bandwidth in the range of 10^-8 to 10^-6 eV from broadband synchrotron radiation, while the reference absorber acts as an energy analyzer for the scattered radiation by the sample that contains no Moessbauer isotope. By optimizing the energy bandwidth of the Moessbauer radiation and selecting the appropriate nuclear resonant absorber, it is possible to separate elastic and inelastic scattering components from the scattered radiation, and also to measure the ultrahigh energy resolution inelastic X-ray scattering spectrum in the wide dynamic range. This paper describes the principle and experimental system of this method, and the first feasible applications including the observations of glass transition of polystyrenes with different molecular weights and quasi-elastic scattering spectra of liquid glycerol are shown. The results clearly demonstrate that the developed method is suitable for studying the molecular dynamics in soft matter and paves the way for new applications of non-Moessbauer experiments using a nuclear Bragg monochromator. (author)