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A stable isotope of carbon, having six protons and six neutrons in the nucleus. Carbon-12 makes up most naturally occurring carbon.
American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
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The radiative capture reaction rate refers to the reaction between a carbon-12 nucleus and a helium nucleus, also known as an alpha particle, that takes place within a star.
The technique relies on knowledge of the levels of two kinds of carbon, carbon-12 and carbon-14," said Wada.
Carbon in sugars originating from flowers is much higher in the isotope carbon-12, whereas sugars originating from sugar cane or corn are much higher in isotope carbon-13 levels.
Burger also identified a shift from heavier carbon-13 to lighter carbon-12; the latter results from burning fossil fuels .
"In sediment records, when you look at the ratio of carbon-12 to carbon-13 in a particular species, you see that it's stable and then it abruptly shifts, wiggles back and forth and slowly returns to pre-event values over hundreds of thousands of years," Schaller said.
But the researchers used methanol ice that contained a variety of carbon known as carbon-13; any contaminants would have carried the slightly lighter carbon-12. By seeing carbon-13 in the ribose and other sugars, the researchers knew chemical reactions in the ice, and not uninvited interlopers, were responsible for the results.
Isotopes are variants of the same chemical element with different atomic weights due to having different numbers of neutrons, such as the most common carbon isotope, carbon-12, and a heavier stable isotope, carbon-13.
The technique compares the amount of carbon-14 (C-14), a less common form of atmospheric carbon, to carbon-12 (C-12), which is more stable and abundant.
Carbon-14 is a heavier isotope of carbon than the 'regular' carbon-12 and, moreover, it is radioactive.
By analyzing the proportions of CO2 molecules containing the different carbon isotopes, scientists have found that the percentage of CO2 containing the Carbon-12 isotope is increasing.