NCIt definition : A version of a chemical element that has an unstable nucleus and emits radiation during
its decay to a stable form. (online dictionary);
Alternative definition : NCI-GLOSS: An unstable form of a chemical element that releases radiation as it breaks
down and becomes more stable. Radioisotopes may occur in nature or be made in a laboratory.
In medicine, they are used in imaging tests and in treatment.; CDISC: An unstable isotope of an element that decays or disintegrates spontaneously,
emitting energy (radiation). (NTI);
Codes from synonyms : CDR0000476884; CDR0000045856;