Fissiooni

Fissiooni, in English often rendered as fission, is the act of splitting a body into two or more parts. The word derives from the Latin fissio, meaning a breaking, from findere, to split. In science, fissiooni most commonly refers to two related but distinct processes: nuclear fission and binary fission.

Nuclear fission is the process by which a heavy atomic nucleus splits into lighter nuclei, typically after absorbing a neutron. This reaction releases energy and several more neutrons, which can induce further fission in nearby nuclei, potentially creating a self-sustaining chain reaction. Nuclear fission is the principal mechanism behind both nuclear power and atomic weapons. The most commonly used fissile fuels are uranium-235 and plutonium-239. Key concepts include critical mass, neutron economy, and fission products—often highly radioactive isotopes formed by the split. Fission can occur with slow (thermal) neutrons or fast neutrons, and the energy released per fission is about 200 MeV. Delayed neutrons play a crucial role in enabling controlled reactor operation.

Binary fission is a form of asexual reproduction observed in many prokaryotes, such as bacteria and some archaea. In this process, the cell replicates its genetic material, elongates, and then divides by a septum to form two genetically identical daughter cells. Binary fission allows rapid population growth under favorable conditions and does not involve mitosis, which is characteristic of eukaryotic cell division.

The term fissiooni also appears in broader contexts to denote any splitting or fragmentation. Related concepts include fissile materials, fission fragments, and the study of fragmentation processes in physics and materials science.