Nuclear resonance spectroscopy

[JRomans]

This method is commonly understood as the Moessbauer spectroscopy in the time-domain. The big pros of this method come from the fact that it uses synchrotron radiation, which has very high intensity, transverse coherence and polarized beams.
Here, same as in Moessbaure spectroscopy, the nuclear energy levels are excited (keV range) by synchrotron radiation pulse. The beam properties of synchrotron are in the keV range with typical meV range energy bandwidth. This means that all hyperfine energy levels are excited simultaneously (energy range around 100 neV).
Then the re-emitted light from the excited sample of interest is collected by detector. The radiation that is emitted from different hyperfine levels differs by very small amounts it can interfere with neigboring energy levels. This results in “time-spectrum” (intensity measurement as a function of time) with quantum-beat/Moire pattern due to the lifetime of each state. If now this spectrum is Fourier transformed the frequencies of these transitions can be observed. From here the hyperfine parameters can be deducted (hyperfine magnetic field, quadrupole splitting, isotope shift). Near the nuclear resonance energy very strong scattering is observed, that is much stronger than electoronic resonances. The amplitude of this nuclear scattering is dependent on electronic and nuclear contribution to the scattering length. The nuclear scattering length is given for a single, unsplit resonance (no hyperfine interaction). Nuclear scattering length is a very sensitive function of the orientation of magnetization direction m (relative to the incident synchrotron wave vector k). Therefore, nuclear resonant scattering is a very sensitive probe of the local spin strictures in magnetic materials.

Features of the technique: the technique is very sensitive of the direction of the hyperfine magnetization and electric field gradient of the sample with respect to the polarization vector of the incoming radiation as well as to the k vector of the incoming radiation.

As Moessbauer effect is taking place in this scattering, the technique as well as isotopic sensitivity. UHV conditions are achievable for this technique. Very sensitive technique, up to monolayer/submonolayer sensitivity, as well as depth and magnetic fluctuation sensitivity is observed among other features.

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