Nuclear Resonant Scattering (NRS) – is a experimental method obtaining energy distribution of nuclear inelastic absorption and emission. This method uses synchrotron radiation to excite nuclei from ground state to very sharp excited energy levels. Then after some delay we have nuclei decay or resonant scattering and this is registered in the time scale.
Synchrotron radiation is used because of its brilliance. This light pulse from electron bunch coherently excited all nuclei to different hyperfine energy levels. The small size and high collimation of the synchrotron beam induces nuclear small angle scattering.
Upton the excitation if the energy of the radiation coincides with the energy of the nuclear levels it excited the nuclei and is re-emitter with a time delay determined by the life time of the energy level ( in the case of 57-Fe sample excitation energy is E=14.4keV and lifetime t= 140ns). In the decay process we have a lot of energy decays at the same time. Thus we have interference of different waves from transition, with slightly different frequencies. Thus we have superposition of all of them , amplitudes interfere giving rise to oscillations in the scattered intensity with time. This is called time beats.
Upon this excitation Electric charges and magnetic moments surrounding the nucleus may shift and split the nuclear energy levels. The shifts and splittings of the energy levels can be used to probe the environment in which the nucleus is embedded.