Alpha Decay
A radioactive decay process in which an unstable heavy nucleus emits an alpha particle (Helium-4 nucleus, ⁴₂He²⁺).
Governing formula
ᴬ_Z X → ᴬ⁻⁴_(Z-2) Y + ⁴₂He (Q_alpha = E_kinetic)
SI unit
MeV (Kinetic Energy)
In depth
Occurs in heavy nuclides (Z > 82) to reduce Coulomb repulsion. The alpha particle tunnels through the nuclear potential barrier via quantum tunneling. Alpha particles have low penetration depth and are stopped by a sheet of paper.
Examples in the real world
Uranium-238 decaying into Thorium-234 by emitting an alpha particle with ~4.2 MeV kinetic energy.