Carbon-11 is a radioactive isotope of carbon, which means it has an unstable nucleus that emits radiation as it decays. It has a mass number of 11, consisting of 6 protons and 5 neutrons. This isotope is commonly used in positron emission tomography (PET) scans, a medical imaging technique that helps visualize metabolic processes in the body. The half-life of Carbon-11 is about 20 minutes, making it suitable for short-term studies in medical research. It is often produced in particle accelerators or cyclotrons and can be incorporated into various organic compounds, allowing scientists to trace biological pathways and diagnose diseases effectively.