Similar term(s): radioactive.
The spontaneous emission of ionizing radiation from the nucleus of an unstable
atom. Radioisotopes lose particles and energy through this process.
Source: GreenFacts, based on Energy Information Administration
Radioactive refers to anything that is caused by, or exhibits
Radioactivity is measured in becquerel (Bq).
Radiation - Radioactive decay - Radioactive material - Radioactive waste
To read about this term in context:
GreenFacts Summary on the Chernobyl Nuclear Accident: