Simply by being radioactive or not. An isotope is an atomic variant of the same element, and has the same chemical characteristics, but is not necessarily radioactive.
Not all isotopes are radioactive; the radioactive isotopes are unstable and emit radiations.
Both isotopes and radioactive isotopes are pretty much the same but radioactive isotopes are better because it can be used to make medicine.
Sodium has no radioactive isotopes.
Radioactive isotopes are not stable.
All the uranium isotopes are radioactive.
All radioactive isotopes will disintegrate.
All isotopes of francium are radioactive.
radioactive isotopes! :)
Some examples are deuterium and tritium which are radioactive isotopes of hydrogen.
There are no radioactive isotopes of boron that are ordinarily found in nature. All elements have synthetic radioactive isotopes, however.
No radioactive isotopes of neon are ordinarily found in nature. All elements have radioactive synthetic isotopes, however.
Not all of the transition elements are radioactive. Many of them are, and some of them have common radioactive isotopes, but some of them have no naturally occurring radioactive isotopes. Please note that all elements have synthetic radioactive isotopes, at least.