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Only 13 of the 38 known-but-unstable elements have isotopes with a half-life of at least 100 years. Every known isotope of the remaining 25 elements is highly radioactive; these are used in academic research and sometimes in industry and medicine.
The unstable (radioactive) isotopes are either primordial or postprimordial. Primordial isotopes were a product of stellar nucleosynthesis or another type of nucleosynthesis such as cosmic ray spallation, and have persisted down to the present because their rate of decay is very slow (e.g. uranium-238 and potassium-40).
This is a list of radioactive nuclides (sometimes also called isotopes), ordered by half-life from shortest to longest, in seconds, minutes, hours, days and years. Current methods make it difficult to measure half-lives between approximately 10 −19 and 10 −10 seconds. [1]
Graph of nuclides (isotopes) by type of decay. Orange and blue nuclides are unstable, with the black squares between these regions representing stable nuclides. The continuous line passing below most of the nuclides comprises the positions on the graph of the (mostly hypothetical) nuclides for which proton number would be the same as neutron ...
A radionuclide (radioactive nuclide, radioisotope or radioactive isotope) is a nuclide that has excess numbers of either neutrons or protons, giving it excess nuclear energy, and making it unstable.
Fluorine-20 is an unstable isotope of fluorine. It has a half-life of 11.0062(80) s and decays via beta decay to the stable nuclide 20 Ne. Its specific radioactivity is 1.8693(14) × 10 +21 Bq/g and has a mean lifetime of 15.879(12) s.
In addition, twenty-nine unstable tin isotopes are known, including tin-100 (100 Sn) (discovered in 1994) [4] and tin-132 (132 Sn), which are both "doubly magic". The longest-lived tin radioisotope is tin-126 (126 Sn), with a half-life of 230,000 years. The other 28 radioisotopes have half-lives of less than a year.
A synthetic radioisotope is a radionuclide that is not found in nature: no natural process or mechanism exists which produces it, or it is so unstable that it decays away in a very short period of time. [1] Frédéric Joliot-Curie and Irène Joliot-Curie were the first to produce a synthetic radioisotope in the 20th century. [2]