All elements with atomic numbers greater than 83 areradioisotopes meaning that these elements haveunstable nuclei and are radioactive. Elements with atomic numbers of 83 and less, have isotopes (stablenucleus) and most have at least one radioisotope (unstable nucleus).
A Radioisotope is also an isotope by nature. The difference is that radioisotopes are very unstable and contain high levels of nuclear energy and emit this energy in the form of nuclear radiation. Main difference: Isotopes can be stable or unstable, but Radioisotopes are always unstable.
