How are alpha particles made from atomic nuclei?

Alpha particles are produced through a process known as alpha decay, a type of radioactive disintegration where an unstable atomic nucleus ejects an alpha particle to dissipate excess energy.1

An alpha particle consists of two protons and two neutrons, effectively acting as a helium nucleus. Because these particles are held within the nucleus by a force that the particles lack sufficient energy to overcome, they cannot escape according to the laws of classical physics. Instead, their emission is explained by quantum mechanics through a phenomenon called tunneling.23

In this process, the alpha particle behaves like a wave, allowing it to penetrate the energetically forbidden potential barrier surrounding the nucleus. Once the particle successfully tunnels through this barrier, it is spontaneously ejected from the parent nucleus. This emission results in a daughter nucleus with an atomic number two units lower and a mass number four units lower than the original parent nucleus.231