olemus
keemilise elemendi ebastabiilne isotoop,
mille aatomituum võib iseenesliku tuumalagu tõttu
tekitada radioaktiivset kiirgust;
isotoobid on sama elemendi aatomivariandid,
mis erinevad massiarvult, st neutronite arvult tuumas;
nukliid on aatomivariant, mis on
tuuma koostise ja energiaga laiemalt määratud

Wiktionary:
radionuclide (physics) a radioactive nuclide
Synonyms: radioisotope
nuclide (physics) an atomic nucleus specified by its atomic number and atomic mass

ülevaateid
https://www.youtube.com/watch?v=cKJMk2Oiod0

https://en.wikipedia.org/wiki/Radionuclide

https://www.nrc.gov/reading-rm/doc-collections/cfr/part020/appb/

https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/291128/sp3-101-sp1b-e-e.pdf

https://www.bipm.org/documents/20126/53814638/Monographie+BIPM-5+-+Comments+%282010%29.pdf/4c77cfc0-8e0a-92f2-e989-3ab369ecd822