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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. [1]
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). Primordial bismuth consists entirely of this isotope.
In this situation it is generally uncommon to talk about half-life in the first place, but sometimes people will describe the decay in terms of its "first half-life", "second half-life", etc., where the first half-life is defined as the time required for decay from the initial value to 50%, the second half-life is from 50% to 25%, and so on.
Carbon (6 C) has 14 known isotopes, from 8 C to 20 C as well as 22 C, of which 12 C and 13 C are stable.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 reactio
Like all artificial elements, it has no stable isotopes. The first isotope to be synthesized was 245 Cf in 1950. There are 20 known radioisotopes ranging from 237 Cf to 256 Cf and one nuclear isomer, 249m Cf. The longest-lived isotope is 251 Cf with a half-life of 898 years.
Six isotopes of flerovium are known, ranging in mass number between 284 and 289; the most stable of these, 289 Fl, has a half-life of ~2.1 seconds, but the unconfirmed 290 Fl may have a longer half-life of 19 seconds, which would be one of the longest half-lives of any nuclide in these farthest reaches of the periodic table.
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 ...
The most stable known roentgenium isotope, 282 Rg, is also the heaviest known roentgenium isotope; it has a half-life of 100 seconds. The unconfirmed 286 Rg is even heavier and appears to have an even longer half-life of about 10.7 minutes, which would make it one of the longest-lived superheavy nuclides known; likewise, the unconfirmed 283 Rg ...