How does nuclear fission release energy in an atomic bomb?

In an atomic bomb, energy is released through the process of nuclear fission, where the nucleus of a heavy atom—typically uranium-235 or plutonium-239—splits into two lighter nuclei of roughly equal mass.12

This process occurs when a fissionable nucleus is struck by a neutron, causing it to become unstable and break apart. This reaction releases a significant amount of energy, along with several additional free neutrons. The released energy is a result of the increase in binding energy per nucleon that occurs when the heavy nucleus splits into smaller, more stable fragments.123

In a weapon, this process is harnessed through a chain reaction. The neutrons emitted from the initial fission event strike other nearby fissile nuclei, inducing further fissions and releasing even more neutrons and energy. When this reaction is uncontrolled and proceeds with extreme rapidity, it generates an enormous amount of energy in a fraction of a second, resulting in a devastating explosion.142