Carbon-13 is a stable isotope of carbon, meaning it does not undergo radioactive decay. It has six protons and seven neutrons in its nucleus, giving it a mass number of 13. This isotope makes up about 1.1% of all naturally occurring carbon. Carbon-13 is important in various scientific fields, particularly in nuclear magnetic resonance (NMR) spectroscopy and stable isotope analysis. These techniques help researchers study molecular structures and track carbon cycling in the environment, providing valuable insights into biological and geological processes.