Alpha Decay
Radioactive decay in which a nucleus emits a helium-4 nucleus, losing two protons and two neutrons.
Formula / equation
ᴬ_Z X → ᴬ⁻⁴_Z₋₂ Y + ⁴₂He
Unit
MeV
In depth
Alpha decay is characteristic of very heavy nuclei, for which shedding four nucleons at once is the most efficient route towards stability. Alpha particles are massive and doubly charged, so they ionise intensely but are stopped by a sheet of paper or the outer layer of skin.
Examples in the real world
Uranium-238 decaying to thorium-234; radon-222, whose alpha emission in the lungs poses a real health risk.