Carbon14

Carbon-14, often written as carbon-14 or 14C, is a radioactive isotope of carbon with six protons and eight neutrons. It has a half-life of about 5,730 years and decays by beta emission to nitrogen-14. In nature, 14C occurs at trace levels in the atmosphere and living organisms.

14C is produced in the upper atmosphere when high-energy cosmic rays collide with nitrogen-14, converting it to 14C. The newly formed 14C quickly oxidizes to carbon dioxide and enters the carbon cycle, becoming part of atmospheric CO2 and organic matter through photosynthesis and respiration.

In living organisms, the 14C/12C ratio remains in equilibrium with the atmosphere. After death, exchange with the environment ceases, and the 14C decays to 14N. The remaining amount of 14C declines exponentially, allowing estimation of the time since death by radiocarbon dating or 14C dating.

Radiocarbon dating relies on measuring the current 14C content using techniques such as accelerator mass spectrometry (AMS) or beta counting. Results are expressed as radiocarbon years before present (BP) and are calibrated against a curve to convert to calendar years, due to fluctuations in 14C production and reservoir effects. The practical dating range is up to about 50,000 years; beyond that, the signal becomes indistinguishable from background.

Limitations include atmospheric variations, the Suess effect from fossil fuel burning, reservoir effects in marine samples, and potential contamination. Despite these challenges, 14C dating remains a fundamental tool in archaeology, geology, and paleoclimatology, providing age estimates for organic materials and contextual dating of historical events.