Boron-11 is a stable isotope of the element Boron, which has an atomic number of 5. It consists of 5 protons and 6 neutrons in its nucleus. This isotope is commonly found in nature and makes up about 80% of all naturally occurring boron. Boron-11 is used in various applications, including nuclear reactors and as a neutron capture agent in medical treatments, particularly in boron neutron capture therapy for cancer. Its unique properties make it valuable in both industrial and scientific fields.