Alpha particle
![](/Images/godic/202412/20/Alpha_Decay.svg0546.png")
![A physicist observes alpha particles from the decay of a polonium source in a cloud chamber](/Images/godic/202412/20/Physicist_Studying_Alpha_Rays_GPN-2000-0003810546.jpg")
![Alpha radiation consists of helium-4 nucleus and is readily stopped by a sheet of paper. Beta radiation, consisting of electrons, is halted by an aluminium plate. Gamma radiation is eventually absorbed as it penetrates a dense material. Lead is good at absorbing gamma radiation, due to its density.](/Images/godic/202412/20/Alfa_beta_gamma_radiation.svg0546.png")
![An alpha particle is deflected by a magnetic field](/Images/godic/202412/20/Alphaparticlemagnetic.svg0546.png")
Alpha particles consist of two protons and two neutrons bound together into a particle identical to a helium nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways. Alpha particles are named after the first letter in the Greek alphabet, α. The symbol for the alpha particle is α or α. Because they are identical to helium nuclei, they are also sometimes written as He2+ or 4
2He2+ indicating a helium ion with a +2 charge (missing its two electrons). If the ion gains electrons from its environment, the alpha particle can be written as a normal (electrically neutral) helium atom 4
2He.