Fission & fusion

Fission and fusion

All matter is composed of atoms: incredibly small structures that house different combinations of three particles, known as protons, neutrons, and electrons.

At the center of each atom is a “nucleus” (the plural of which is “nuclei”), where neutrons and protons are bound in close proximity together. Most nuclei are relatively stable, meaning the makeup of their neutrons and protons is comparatively static and unchanging.

During fission, the nuclei of certain heavy atoms split into smaller, lighter nuclei, releasing excess energy in the process. This can sometimes occur spontaneously, but can also, in certain nuclei, be induced from outside. A neutron is shot at the nucleus and is absorbed, causing instability and fission. In some elements—such as certain isotopes of uranium and plutonium—the fission process also releases excess neutrons, which can trigger a chain reaction if they’re absorbed by nearby atoms.

Fusion works in reverse: when exposed to extremely high temperatures and pressures, some lightweight nuclei can fuse together to form heavier nuclei, releasing energy in the process.

In modern nuclear weapons, which use both fission and fusion, a single warhead can release more explosive energy in a fraction of a second than all of the weapons used during World War II combined—including Fat Man and Little Boy, the two atom bombs dropped on Japan.