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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.
Bismuth-209 (209 Bi) is an isotope of bismuth, with the longest known half-life of any radioisotope that undergoes α-decay (alpha decay).It has 83 protons and a magic number [2] of 126 neutrons, [2] and an atomic mass of 208.9803987 amu (atomic mass units).
There is a half-life describing any exponential-decay process. For example: As noted above, in radioactive decay the half-life is the length of time after which there is a 50% chance that an atom will have undergone nuclear decay. It varies depending on the atom type and isotope, and is usually determined experimentally. See List of nuclides.
Radioactive decay is seen in all isotopes of all elements of atomic number 83 or greater. Bismuth-209, however, is only very slightly radioactive, with a half-life greater than the age of the universe; radioisotopes with extremely long half-lives are considered effectively stable for practical purposes.
Some older sources give the final isotope as bismuth-209, but in 2003 it was discovered that it is very slightly radioactive, with a half-life of 2.01 × 10 19 years. [ 9 ] There are also non-transuranic decay chains of unstable isotopes of light elements, for example those of magnesium-28 and chlorine-39 .
The longest-lived radioisotopes are 205 Pb with a half-life of 17.3 million years and 202 Pb with a half-life of 52,500 years. A shorter-lived naturally occurring radioisotope, 210 Pb with a half-life of 22.2 years, is useful for studying the sedimentation chronology of environmental samples on time scales shorter than 100 years. [5]
As an extreme example, the half-life of the isotope bismuth-209 is 2.01 × 10 19 years. The isotopes in beta-decay stable isobars that are also stable with regards to double beta decay with mass number A = 5, A = 8, 143 ≤ A ≤ 155, 160 ≤ A ≤ 162, and A ≥ 165 are theorized to undergo
Considering all decay modes, various models indicate a shift of the center of the island (i.e., the longest-living nuclide) from 298 Fl to a lower atomic number, and competition between alpha decay and spontaneous fission in these nuclides; [83] these include 100-year half-lives for 291 Cn and 293 Cn, [55] [78] a 1000-year half-life for 296 Cn ...