For mono-directional radiation
, the energy
traversing in a time interval over a small area perpendicular to the direction of the energy flow, divided by that time interval and by that area.
PAC, 1994, 66, 2513
(Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994))
on page 2519
IUPAC. Compendium of Chemical Terminology, 2nd ed. (the "Gold Book"). Compiled by A. D. McNaught and A. Wilkinson. Blackwell Scientific Publications, Oxford (1997). XML on-line corrected version: http://goldbook.iupac.org (2006-) created by M. Nic, J. Jirat, B. Kosata; updates compiled by A. Jenkins. ISBN 0-9678550-9-8. doi:10.1351/goldbook