Nuclear

Nuclear refers to phenomena and technologies associated with atomic nuclei. It includes radioactive decay, nuclear fission and fusion, and interactions that emit ionizing radiation. Nuclear energy arises from changes to a nucleus, most commonly by fission in power reactors or by future fusion.

Nuclear physics studies protons and neutrons, binding energy, and processes such as half-life and different decay modes. A chain reaction occurs when neutrons from fission induce further fissions; a reactor remains controlled by managing neutron population, achieving criticality safely.

Applications span electricity generation, medicine, industry, science, and defense. Nuclear power plants generate electricity by converting heat from fission into steam that drives turbines. In medicine, radioactive isotopes are used for diagnosis and treatment, and radiopharmaceuticals are routinely employed. In industry and research, neutron and gamma sources enable imaging and materials analysis.

History includes early 20th-century discoveries of radioactivity and the nuclear model, which laid groundwork for civilian energy programs and weapons development. Fission was discovered in 1938, enabling the Manhattan Project. Nuclear energy expanded after World War II; major accidents at Chernobyl and Fukushima highlighted safety, environmental, and public health concerns.

Governance emphasizes safety, nonproliferation, and verification. The International Atomic Energy Agency promotes peaceful uses of nuclear energy, while the Nuclear Non-Proliferation Treaty seeks to limit weaponization and ensure safeguards and responsible management of nuclear materials.