Total ionization cross section for an incident photon of a given energy interacting with a material to produce one or more photoelectrons from all sub-shells that are energetically accessible.
See also: sub-shell photoionization cross section
Source:
PAC, 2020, 92, 1781. 'Glossary of methods and terms used in surface chemical analysis (IUPAC Recommendations 2020)' on page 1809 (https://doi.org/10.1515/pac-2019-0404)