Nuclear Fission
Nuclear fission is a nuclear reaction in which the nucleus of an atom splits into two or more smaller nuclei, known as fission products. This process typically releases a significant amount of energy, as well as several neutrons and gamma photons.
Discovery of Nuclear Fission
The phenomenon of nuclear fission was first discovered in December 1938 by the German chemists Otto Hahn and Fritz Strassmann, and the theoretical explanation was later provided by the Austrian-Swedish physicist Lise Meitner and her nephew, the British-Austrian physicist Otto Robert Frisch. These discoveries were pivotal in advancing the understanding of nuclear reactions and laid the groundwork for the development of nuclear reactors and nuclear weapons.
The Process of Nuclear Fission
In a typical fission reaction, a heavy nucleus such as uranium-235 or plutonium-239 absorbs a neutron and becomes unstable. This instability causes the nucleus to split into two smaller nuclei along with the release of additional neutrons and a considerable amount of energy. The released neutrons may then go on to induce further fission reactions in nearby nuclei, leading to a nuclear chain reaction.
Nuclear Chain Reaction
A nuclear chain reaction occurs when the neutrons produced by each fission event cause additional fission events to occur. This can lead to a self-sustaining reaction if there are enough fissile nuclei and the conditions are right, which is a critical aspect of both nuclear reactors and nuclear weapons.
Critical Mass
The term "critical mass" refers to the minimum amount of fissile material needed to maintain a self-sustaining chain reaction. If the mass of the fissile material is below this threshold, the reaction will diminish and eventually stop. In contrast, if the mass exceeds this critical point, an uncontrolled chain reaction may occur, potentially leading to an explosion.
Applications of Nuclear Fission
Nuclear Reactors
Nuclear reactors utilize the controlled fission of fissile materials to produce energy. These reactors are the heart of nuclear power plants and are used to generate electricity, as well as for some types of naval propulsion.
The first artificial nuclear reactor, known as Chicago Pile-1, was built by a team led by physicist Enrico Fermi in 1942, marking the advent of the Atomic Age.
Nuclear Weapons
Nuclear weapons derive their destructive power from nuclear fission reactions. The first nuclear bombs used during World War II were fission-based weapons, such as those dropped on Hiroshima and Nagasaki in 1945. These weapons operate on the principle of quickly assembling a supercritical mass of fissile material to produce an explosive chain reaction.
Natural Nuclear Fission Reactors
A natural nuclear fission reactor is a uranium deposit where self-sustaining nuclear chain reactions have occurred naturally. The most famous example is the Oklo natural nuclear reactor in Gabon, West Africa, which was active around 2 billion years ago.