Alpha particle
During alpha decay, the atomic nucleus releases an alpha particle. The nucleus will lose two protons and two neutrons when this happens. After the decay, the atom will change to another element, because the atom loses two protons.  For example, when americium goes through alpha decay it changes into neptunium because neptunium is defined to have two protons less than americium.  Alpha decay usually happens in heavy elements, those containing more neutrons and protons, such as uranium, thorium, plutonium, and radium.