C13C14

Carbon has several isotopes, among which carbon-13 (C-13) and carbon-14 (C-14) are particularly significant due to their stability and applications. C-13 is a stable isotope with 6 protons and 7 neutrons, making up about 1.1% of natural carbon. C-14 is radioactive, with 6 protons and 8 neutrons, and it decays by beta emission with a half-life of 5,730 years. It occurs only in trace amounts in nature.

Natural abundance and production: C-13 arises from stellar nucleosynthesis and is incorporated into all natural carbon reservoirs. C-14 forms in the atmosphere through interactions of cosmic rays with nitrogen-14; it then mixes with atmospheric carbon and enters living organisms via CO2 and the food chain. Because of its radioactivity, C-14 is used for dating and tracing.

Measurement methods: C-13 is typically measured by isotope ratio mass spectrometry (IRMS) to determine the 13C/12C ratio, enabling stable isotope labeling studies and tracing of metabolic pathways. C-14 is measured by accelerator mass spectrometry (AMS) or by beta counting in older methods; the measured 14C/12C ratio is compared to a standard to determine age.

Applications: C-13 labeling is widely used in chemistry, biochemistry, and ecology to follow substrate fate and quantify reaction mechanisms. C-14 is the basis of radiocarbon dating, allowing age estimates for organic materials up to about 50,000 years, with calibration curves to account for past variations in atmospheric C-14. The mid-20th century nuclear testing created a “bomb pulse” that provides high-resolution data for recent turnover studies.

Limitations: dating accuracy depends on preservation, contamination, and reservoir effects; stable C-13 analyses require correction for fractionation; C-14 measurements require specialized facilities.