Alpha Decay

$\alpha$ decay is when an atom loses a helium nucleus

${}_{}^{}{}_{\mathrm{Z}}^{\mathrm{A}}\mathrm{X}\to {}_{}^{}{}_2^4\mathrm{He}+{}_{}^{}{}_{\mathrm{Z}-2}^{\mathrm{A}-4}\mathrm{Y}$