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 commonly used in scientific research, particularly in NMR spectroscopy and stable isotope analysis. These techniques help scientists study molecular structures and track carbon flow in ecosystems, providing valuable insights into biological and environmental processes.