beryllium8

Beryllium-8 (8Be) is a light, unstable isotope of beryllium. It has 4 protons and 4 neutrons (Z = 4, N = 4) and a mass number of 8. The ground-state spin-parity is 0+. The nucleus is not bound; it exists only as a fleeting resonance that decays into two alpha particles (two 4He nuclei) with a half-life on the order of 10^-16 seconds. Be-8 is unbound by about 92 keV with respect to the alpha-decay threshold, which gives it a very short lifetime and makes it effectively non-stable except when formed in reactions.

In stellar environments, Be-8 is formed transiently during helium burning as an intermediate in the triple-alpha process. Two alpha particles fuse to form Be-8, which can capture a third alpha particle to produce carbon-12 in an excited Hoyle state before settling into carbon-12. This sequence enables the synthesis of carbon in stars and is a key part of how heavier elements are produced in the universe.

In nuclear physics, Be-8 is often described as a resonance with a cluster structure resembling two tightly bound alpha particles. Its extremely short lifetime reflects its position above the two-alpha threshold and its strong interaction decay mode. Be-8 has little presence as a stable material on Earth, but its properties illuminate alpha clustering and the mechanisms that enable stellar nucleosynthesis.