precursor

in radioanalytical chemistry
https://doi.org/10.1351/goldbook.P04805
Of a nuclide, any radioactive nuclide which precedes that nuclide in a decay chain.
Source:
PAC, 1994, 66, 2513. 'Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)' on page 2523 (https://doi.org/10.1351/pac199466122513)