quadrupole splitting

in Mössbauer spectroscopy
https://doi.org/10.1351/goldbook.Q04972
The measured Doppler velocity difference between the two peaks seen in quadrupole split spectra from @[email protected] such as 57Fe and 119Sn.
Source:
PAC, 1976, 45, 211. (Nomenclature and Conventions for Reporting Mössbauer Spectroscopic Data) on page 214 [Terms] [Paper]