Radioactive decay
During alpha decay, the atomic nucleus releases an alpha particle. Alpha decay causes the nucleus to lose two protons and two neutrons. Alpha decay causes the atom to change into another element, because the atom loses two protons (and two neutrons). For example, if Americium were to go through alpha decay it would change into Neptunium because Neptunium is defined by having two protons fewer than Americium. Alpha decay usually happens in the most heavy elements, such as uranium, thorium, plutonium, and radium.