Of an irradiated element for a specified isotope, the steady state reached when the disintegration rate of the nuclide formed is equal to its production rate.
Source:
PAC, 1994, 66, 2513. 'Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)' on page 2525 (https://doi.org/10.1351/pac199466122513)