Alpha decay occurs when an atomic nucleus disintegrates by emitting alpha particles. An alpha particle consists of two protons and two neutrons; it is the nucleus of a helium atom. Alpha decay is most often observed in high- as opposed to low-mass nuclear decay. Elements of high atomic mass are relatively less stable than objects of lower atomic mass, and are more likely to undergo the process of alpha decay.

These high-mass elements can be compared to a top-heavy pick-up truck. If the truck is filled beyond a stable capacity, it may throw off some of its contents. In the same way, alpha particles are released by radioactive material as a means of achieving greater stability. When radioactive material or other unstable nuclei break down, there is a loss in the total mass of the products of this reaction. A loss of mass results in a...