radioactive source

https://doi.org/10.1351/goldbook.R05088
Any quantity of radioactive material which is intended for use as a source of ionizing radiation.
Source:
PAC, 1994, 66, 2513. 'Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994)' on page 2525 (https://doi.org/10.1351/pac199466122513)