Beryllium-10 (Be) is a radioisotope of beryllium. It is formed in the Earth's atmosphere mainly by cosmic ray spallation of nitrogen and oxygen. Beryllium-10 has a half-life of 1.39 × 10 years. It decays by beta decay to boron-10. It has a maximum energy of 556.2 keV. It decays through the reaction Be→B + e.