How does nuclear fission release energy?

Nuclear fission releases energy by splitting a heavy atomic nucleus into smaller nuclei, releasing energy in the process.

In more detail, nuclear fission occurs when a heavy nucleus, such as uranium-235 or plutonium-239, absorbs a neutron. This absorption makes the nucleus unstable, causing it to split into two smaller nuclei, known as fission fragments. Along with these smaller nuclei, a few more neutrons and a significant amount of energy are released. The energy comes from the strong nuclear forces that hold the nucleus together. When the nucleus splits, some of this binding energy is converted into kinetic energy of the fission fragments and the emitted neutrons, as well as electromagnetic radiation in the form of gamma rays.

The released neutrons can go on to collide with other heavy nuclei, causing them to undergo fission as well. This can create a chain reaction, which is the principle behind both nuclear reactors and nuclear weapons. In a nuclear reactor, this chain reaction is carefully controlled to release energy steadily, which is then used to produce electricity. In a nuclear weapon, the chain reaction is uncontrolled, leading to a massive release of energy in a very short time.

The energy released in nuclear fission is enormous compared to chemical reactions. For example, the fission of one uranium-235 nucleus releases about 200 million electron volts (MeV) of energy, whereas burning a single molecule of methane releases only a few electron volts. This high energy density is why nuclear power is such a potent source of energy.

Understanding nuclear fission involves concepts from both physics and chemistry, including the structure of the atom, the forces within the nucleus, and the behaviour of neutrons. It's a fascinating process that has both powerful applications and significant implications for energy production and safety.