Carbon-14
Definition and meaning of Carbon-14 in chemistry.
Carbon-14 is a naturally occurring radioactive isotope of carbon whose nucleus contains 6 protons and 8 neutrons, giving it a mass number of 14 and a half-life of about 5,730 years.
In more detail
It forms continuously in the upper atmosphere when cosmic-ray neutrons collide with nitrogen-14 nuclei, then oxidizes to carbon dioxide that living organisms take up through photosynthesis or the food chain. While an organism is alive, its carbon-14 level stays in equilibrium with the atmosphere; once it dies, uptake stops and the carbon-14 decays at a fixed, known rate through beta-minus decay back to nitrogen-14. Comparing the remaining activity to that of living material lets scientists calculate elapsed time, the basis of radiocarbon dating.
Key facts
| Symbol | ¹⁴C (or C-14) |
|---|---|
| Half-life | 5,730 ± 40 years |
| Decay mode | Beta-minus decay to nitrogen-14 |
| Field | Analytical Chemistry |
A wooden artifact whose carbon-14 activity has fallen to 25% of that in modern living wood has passed through two half-lives, meaning it is roughly 11,460 years old.
Frequently asked questions
How is carbon-14 used to date objects?
Scientists measure the remaining carbon-14 activity (or count of C-14 atoms) in an organic sample and compare it to the level found in living organisms; applying the known half-life gives the time elapsed since the organism died, typically reliable for objects up to about 50,000 years old.
Why is carbon-14 radioactive while carbon-12 is stable?
Carbon-14 has two extra neutrons relative to carbon-12, making its nucleus neutron-rich and unstable; it reaches a more stable configuration by converting a neutron into a proton via beta-minus decay, emitting an electron and an antineutrino and becoming nitrogen-14.