- Isotope of an element which is unstable and prone to radioactive decay. Because the decay occurs at a known rate (half-life), some radioisotopes can be used for dating rocks and meteorites.
- For a given chemical element, an isotope which exhibits radioactivity. radium, for instance, as over 30 identified isotopes, all of which are radioactive. Also spelled radio isotope. Also called radioactive isotope, radio element (2), or unstable isotope.
- synonymradio element
- synonymradioactive isotope
- noun a natural or artificial isotope which gives off radiation