A species of atom, characterized by its
mass number,
atomic number and nuclear energy state, provided that the
mean life in that state is long enough to be observable.
Source:
PAC, 1994, 66, 2513
(Nomenclature for radioanalytical chemistry (IUPAC Recommendations 1994))
on page 2522
PAC, 1982, 54, 1533
(Glossary of terms used in nuclear analytical chemistry (Provisional))
on page 1547