Setup for the NFS measurement. The pulsed SR (left side, pulses separated by Dt) penetrates the sample and reaches the detector. The decay of the nuclear excited states, which takes place in the time window Dt (right side), reflects the hyperfine interactions of the resonant nuclei.
When a synchrotron radiation pulse penetrates the sample containing resonant nuclei, then
- electric charge scattering
happens almost instantaneously (t £10-15 s)
- while the processes involving
nuclear excitations are delayed:
the mean life time of the excited state of 57Fe is 141ns.
Therefore, it is possible to separate the events originating from nuclear and electronic scattering in the sample.
Since the incident beam is broad in energy compared to the nuclear level width (4.7neV for 57Fe) or the hyperfine splitting of these levels (less than 1 meV),