resonance cross-section

in Mössbauer spectrometry
https://doi.org/10.1351/goldbook.R05329
The cross-section for resonant absorption of the Mössbauer transition γ ray.
Source:
PAC, 1976, 45, 211. 'Nomenclature and Conventions for Reporting Mössbauer Spectroscopic Data' on page 214 (https://doi.org/10.1351/pac197645030211)