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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).
The longest-lived radioisotope is 14 C, with a half-life of 5.70(3) × 10 3 years. This is also the only carbon radioisotope found in nature, as trace quantities are formed cosmogenically by the reaction 14 N + n → 14 C + 1 H. The most stable artificial radioisotope is 11 C, which has a half-life of 20.3402(53) min. All other radioisotopes ...
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 ...
However, radioactive iodine is a disproportionate biohazard because the thyroid gland concentrates iodine. 129 I has a half-life nearly a billion times as long as its more hazardous sister isotope 131 I; therefore, with a shorter half-life and a higher decay energy, 131 I is approximately a billion times more radioactive than the longer-lived ...
The next group is the primordial radioactive nuclides. These have been measured to be radioactive, or decay products have been identified in natural samples (tellurium-128, barium-130). There are 35 of these (see these nuclides), of which 25 have half-lives longer than 10 13 years. With most of these 25, decay is difficult to observe and for ...
The longest-lived of these is 133 Ba, which has a half-life of 10.51 years. All other radioisotopes have half-lives shorter than two weeks. The longest-lived isomer is 133m Ba, which has a half-life of 38.9 hours. The shorter-lived 137m Ba (half-life 2.55 minutes) arises as the decay product of the common fission product caesium-137.
Other than the naturally occurring isotopes, the longest-lived radioisotopes are 151 Sm, which has a half-life of 94.6 years, [6] and 145 Sm, which has a half-life of 340 days. All of the remaining radioisotopes, which range from 129 Sm to 168 Sm, have half-lives that are less than two days, and the majority of these have half-lives that are ...