nuclear resonant scattering is a method in which a synchrotron light source is used to excite different levels that are splitted only by hyperfine splitting. If we measure the outcoming photons, we can plot this as a function of time and obtain a superposition of different beating frequencies. Measuring these individual frequencies allows us to calculate the energy differences between these states by using the energy-time uncertainty principle.
NRS is a great technique with polarization, k-vector and magnetization direction sensitivity and it is great for examining hyperfine properties such as the hyperfine field, the quadrupole shift and the isomeric shift.