Quadrupole splitting is an example of a hyperfine interaction

Hyperfine structure

The term hyperfine structure refers to a collection of different effects leading to small shifts and splittings in the energy levels of atoms, molecules and ions. The name is a reference to the fine structure which results from the interaction between the magnetic moments associated with electron...

 found in gamma-ray spectroscopy, in the circumstance where nuclei with a non-radially-symmetric shape (that is, with a spin quantum number greater than 1/2) are found immersed in an external electric field gradient. It splits a state into two, producing a doublet in the Mossbauer spectrum, and the separation between the states can be used to measure the sign and strength of this electric field gradient, which is affected by the chemical environment of the nuclei.