Definition & Betydelse | Engelska ordet CARBON-12

Definition av CARBON-12

1. (kemi) kol-12

Exempel på hur man kan använda CARBON-12 i en mening

• Nuclear fusion reaction of two helium-4 nuclei produces beryllium-8, which is highly unstable, and decays back into smaller nuclei with a half-life of , unless within that time a third alpha particle fuses with the beryllium-8 nucleus to produce an excited resonance state of carbon-12, called the Hoyle state, which nearly always decays back into three alpha particles, but once in about 2421.
• For example, due to a different mixture of stable carbon-12 and carbon-13 isotopes, a sample of elemental carbon from volcanic methane will have a different relative atomic mass than one collected from plant or animal tissues.
• In 1951 Salpeter suggested that stars could burn helium-4 into carbon-12 with the Triple-alpha process not directly, but through an intermediate metastable state of beryllium-8, which helped to explain the carbon production in stars.
• For example, isotopes of carbon include carbon-12, carbon-13, carbon-14, which contain 6, 7, 8 neutrons respectively, but all contain 6 protons.
• The addition of another helium 4 nucleus to the beryllium yields carbon-12, followed by oxygen-16, neon-20 and so on, each time adding 2 protons and 2 neutrons to the growing nucleus.
• The preponderance of sulfur-32 is explained by its production from carbon-12 plus successive fusion capture of five helium-4 nuclei, in the so-called alpha process of exploding type II supernovas (see silicon burning).
• Most oxygen-16 is synthesized at the end of the helium fusion process in stars; the triple-alpha process creates carbon-12, which captures an additional helium-4 to make oxygen-16.
• Examples include boron-10, carbon-12, and nitrogen-14 (as N − Z = 0 for each pair), or boron-12, carbon-14, and nitrogen-16 (as N − Z = 2 for each pair).
• Now known as Leona Marshall Libby, she became interested in ecological and environmental issues, and she devised a method of using the isotope ratios of oxygen-18 to oxygen-16, carbon-13 to carbon-12, and deuterium to hydrogen in tree rings to study changes in temperature and rainfall patterns hundreds of years before records were kept, opening the door to the study of climate change.
• The argument for keeping the term "atomic weight" was primarily that it was a well understood term to those in the field, that the term "atomic mass" was already in use (as it is currently defined) and that the term "relative atomic mass" might be easily confused with relative isotopic mass (the mass of a single atom of a given nuclide, expressed dimensionlessly relative to 1/12 of the mass of carbon-12; see section above).
• The analysis of ratios of carbon-13 to carbon-12 along the length of a single elephant hair led Cerling and his crew to understand the elephants' diet.
• On average, the ratio of carbon-12 to carbon-13 matches that of the Earth's atmosphere, while that of nitrogen-14 to nitrogen-15 matches the Sun.
• In stars as massive as the Sun, carbon-12 is also converted to carbon-13 and then onto nitrogen-14 by fusion with protons.

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