What is "radioisotopes"

Usage examples of "radioisotopes".

This depends on injecting very short-lived and presumably non-hazardous radioisotopes into the bloodstream and then detecting, by means of their emission of positrons, where they are in the brain at times up to half an hour or so after injection.

Such processes are incapable of selecting radioisotopes to use for the manufacture of enzymes.

Chemically the enzyme will behave the same whether it has radioisotopes in it or not.

So, how could the enzyme have selected radioisotopes to build into itself?