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 [Terms] [Paper]