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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
Carbon-13 has a non-zero spin quantum number of 1 / 2 , and hence allows the structure of carbon-containing substances to be investigated using carbon-13 nuclear magnetic resonance. The carbon-13 urea breath test is a safe and highly accurate diagnostic tool to detect the presence of Helicobacter pylori infection in the stomach. [4]
The half-life of a radioactive isotope (usually denoted by t 1/2) is a more familiar concept than the mean-life, so although the equations above are expressed in terms of the mean-life, it is more usual to quote the value of 14 C 's half-life than its mean-life. The currently accepted value for the half-life of 14 C is 5,700 ± 30 years. [21]
About 99% of carbon on Earth is carbon-12 (12 C), about 1% is carbon-13 (13 C), and a trace amount is carbon-14 (14 C). The 12 C and 13 C isotopes are stable, while 14 C decays radioactively to nitrogen-14 (14 N) with a half-life of 5730 years. 14 C on Earth is produced nearly exclusively by the interaction of cosmic radiation with the upper ...
There are 15 known isotopes of carbon and the shortest-lived of these is 8 C which decays through proton emission and has a half-life of 3.5 × 10 −21 s. [15] The exotic 19 C exhibits a nuclear halo, which means its radius is appreciably larger than would be expected if the nucleus were a sphere of constant density. [76]
The limit of measurability is approximately eight half-lives, or about 45,000 years. Samples older than this will typically be reported as having an infinite age. Some techniques have been developed to extend the range of dating further into the past, including isotopic enrichment, or large samples and very high precision counters.
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The ratio of carbon-13 and carbon-12 isotopes in these types of plants is as follows: [11] C 4 plants: −16‰ to −10‰ CAM plants: −20‰ to −10‰ C 3 plants: −33‰ to −24‰ Limestones formed by precipitation in seas from the atmospheric carbon dioxide contain normal proportion of 13 C.