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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).
Instead, the half-life is defined in terms of probability: "Half-life is the time required for exactly half of the entities to decay on average". In other words, the probability of a radioactive atom decaying within its half-life is 50%. [2] For example, the accompanying image is a simulation of many identical atoms undergoing radioactive decay.
Isotopes – equal Z; Isobars – equal A; ... Half-life of a radioisotope: t 1/2, T 1/2: ... Defining equation (physical chemistry)
Thus, after 3 half-lives there will be 1/2 3 = 1/8 of the original material left. Therefore, the mean lifetime is equal to the half-life divided by the natural log of 2, or: = / /. For example, polonium-210 has a half-life of 138 days, and a mean lifetime of 200 days.
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
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.
This model defines the island of stability as the region with the greatest resistance to fission rather than the longest total half-lives; [20] the nuclide 306 Ubb is still predicted to have a short half-life with respect to alpha decay. [2] [70] The island of stability for spherical nuclei may also be a "coral reef" (i.e., a broad region of ...