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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.
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.
Other than 87 Rb, the longest-lived radioisotopes are 83 Rb with a half-life of 86.2 days, 84 Rb with a half-life of 33.1 days, and 86 Rb with a half-life of 18.642 days. All other radioisotopes have half-lives less than a day. 82 Rb is used in some cardiac positron emission tomography scans to assess myocardial perfusion. It has a half-life of
The three long-lived nuclides are uranium-238 (half-life 4.5 billion years), uranium-235 (half-life 700 million years) and thorium-232 (half-life 14 billion years). The fourth chain has no such long-lasting bottleneck nuclide near the top, so almost all of the nuclides in that chain have long since decayed down to just before the end: bismuth-209.
Among the known synthetic radioactive isotopes; the most stable one is 163 Ho, with a half-life of 4,570 years. All other radioisotopes have half-lives not greater than 1.117 days in their ground states (although the metastable 166m1 Ho has a half-life of about 1,200 years), and most have half-lives under 3 hours.
The longest-lived of these isotopes, and the most relevantly studied, are 90 Sr with a half-life of 28.9 years, 85 Sr with a half-life of 64.853 days, and 89 Sr (89 Sr) with a half-life of 50.57 days. All other strontium isotopes have half-lives shorter than 50 days, most under 100 minutes.
Forty radioisotopes have been characterized, with the most stable, besides 176 Lu, being 174 Lu with a half-life of 3.31 years, and 173 Lu with a half-life of 1.37 years. All of the remaining radioactive isotopes have half-lives that are less than 9 days, and the majority of these have half-lives that are less than half an hour.
In addition, there are 34 known synthetic radioisotopes, the most stable of which is 182 Hf with a half-life of 8.9 × 10 6 years. This extinct radionuclide is used in hafnium–tungsten dating to study the chronology of planetary differentiation. [5] No other radioisotope has a half-life over 1.87 years. Most isotopes have half-lives under 1 ...
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