In elements with more than 83 protons, all of the isotopes are radioactive.The force of repulsion among all those protons makes the nuclei unstable. Elements with more than 92 protons have such unstable nuclei that they don't even exist in nature. More than 1,000 radioactive isotopes of the various elements are known. Approximately 50 of these are found in nature; the rest are produced artificially as the direct products of nuclear reactions or indirectly as the radioactive descendants of these products. Radioactive isotopes have many useful applications. Stable isotopes are non-radioactive forms of atoms. Although they do not emit radiation, their unique properties enable them to be used in a broad variety of applications, including water and soil management, environmental studies, nutrition assessment studies and forensics.
