Most atomic nuclei in the universe are stable. This means the number of protons in a stable atom's nucleus remains constant indefinitely. Consequently, a stable atom retains its elemental identity regardless of any environmental factors it encounters such as temperature, pressure or chemical reactions. Only two known natural processes give rise to new elements: radioactive decay and thermonuclear fusion.Continue Reading
Radioactive decay refers to the disintegration of unstable isotopes of elements whose nuclei contain a higher number of neutrons than their stable counterparts. These extra neutrons destabilize an atomic nucleus; at some future time, that nucleus will eject a high-energy particle or break apart into smaller daughter nuclei. Either way, the resulting atom(s) consists of different elements than the parent nucleus.
A good example of radioactive decay is the isotope uranium-238, which contains 92 protons and 146 neutrons. In a form of disintegration called alpha decay, uranium-238 releases a helium nucleus containing two protons and two neutrons. The remaining nucleus, thorium-234, contains 90 protons and 144 neutrons. In essence, thorium and helium are created when uranium-238 decays.
While radioactive decay is a ubiquitous process, thermonuclear fusion takes place under unimaginable heat and pressure, namely in the cores of stars. In the most common scenario, four protons fuse to form a helium nucleus and release a tremendous amount of energy. In stellar cores, lighter elements can fuse to form elements as massive as iron. Elements heavier than iron, from cobalt through uranium, form only during a supernova, an explosion so titanic it briefly outshines all of the stars in an entire galaxy.Learn more about Particle Physics