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Fission is a nuclear reaction or a radioactive decay process in which the nucleus of an atom splits into two or more smaller, lighter nuclei. The fission process often produces free neutrons and gamma photons, and releases a very large amount of energy, even by the energetic standards of radioactive decay.

Overview

Nuclear fission of heavy elements was discovered on December 17, 1938 by the German chemists Otto Hahn and Fritz Strassmann, who demonstrated that uranium could be split into parts to yield isotopes of barium and krypton. Following their experimental evidence, Lise Meitner and Otto Robert Frisch explained the process theoretically and named it "fission", drawing an analogy with the division of living cells.

Mechanism

In a fission reaction, a heavy nucleus absorbs a neutron, becoming unstable and splitting into two (or occasionally three) smaller nuclei, along with several neutrons and a large amount of energy. This energy is released in the form of kinetic energy of the fission products (the fragments of the original nucleus) and as electromagnetic radiation in the form of gamma rays. The emitted neutrons may then cause new fissions, which can lead to a self-sustaining chain reaction, the basis for both nuclear reactors and nuclear weapons.

Types of Fission

Fission can occur spontaneously in some heavy isotopes, a process known as spontaneous fission. However, it is more commonly induced by the absorption of a neutron. Depending on the energy of the neutron, fission can be classified as either fast or thermal. In fast fission, high-energy neutrons induce the fission, while in thermal fission, it is caused by lower-energy neutrons.

Applications

The most well-known application of nuclear fission is in nuclear power plants and nuclear weapons. In power plants, controlled fission reactions are used to generate heat, which is then used to produce steam that drives turbines to generate electricity. In nuclear weapons, an uncontrolled fission chain reaction releases a massive amount of energy in a very short time, causing an explosion.

Safety and Environmental Concerns

While nuclear fission can be a source of large amounts of energy without the carbon emissions associated with fossil fuels, it does come with safety and environmental concerns. These include the potential for nuclear accidents, as seen in the Chernobyl disaster and the Fukushima Daiichi nuclear disaster, and the challenge of managing radioactive waste.

Future of Fission

Research into nuclear fission continues, with efforts focused on making fission-based energy safer and more efficient. This includes the development of new types of reactors, such as small modular reactors (SMRs) and generation IV reactors, which promise enhanced safety features, greater fuel efficiency, and reduced waste production.