helium4nuklid

Helium-4 nuclide, designated 4He, is the nucleus that consists of two protons and two neutrons, giving it atomic number Z=2 and mass number A=4. In bound form it is most commonly known as the alpha particle. The ground-state nucleus has spin 0 and positive parity, and carries a charge of +2e.

The 4He nucleus is highly stable for a light nucleus. It has a total binding energy of about 28.3 MeV, corresponding to roughly 7.07 MeV per nucleon, making it unusually tightly bound among light nuclei. In simple nuclear models, Z=2 and N=2 lead to a doubly magic-like configuration, which contributes to its exceptional stability. There are no bound excited states of 4He; it is stable against radioactive decay under ordinary conditions.

In nature, helium-4 is the dominant isotope of helium. It is produced in large amounts during Big Bang nucleosynthesis and is also formed in stellar helium-burning processes. On Earth, nearly all naturally occurring helium is 4He, with a very small fraction of 3He.

4He plays a central role in nuclear physics and astrophysics. It is the end product of many fusion reactions, notably deuterium–tritium fusion, and serves as a straightforward, well-understood bound state that helps test models of the strong interaction and few-body dynamics. In common terminology, the 4He nucleus is referred to as an alpha particle when it appears as a separate constituent in radioactive decay or nuclear reactions.