isomeric state

in nuclear chemistry
https://doi.org/10.1351/goldbook.I03292
A nuclear state having a mean life long enough to be observed.
Source:
PAC, 1982, 54, 1533. 'Glossary of terms used in nuclear analytical chemistry (Provisional)' on page 1545 (https://doi.org/10.1351/pac198254081533)