Of atoms undergoing a nuclear transformation
, that fraction which remains in or reverts to its initial chemical form.
PAC, 1982, 54, 1533
(Glossary of terms used in nuclear analytical chemistry (Provisional))
on page 1551
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