Related Terms. Ratio of the density of a substance at 20Â°C or 68Â°F to the density of water at 4Â°C or 39.2Â°F.
Nuclear fission. NUCLEAR FISSION. Nuclear fission is a reaction in which an atom's nucleus is broken apart, releasing a tremendous amount of energy. Nuclear fission is used in many power plants on Earth (and is used in atomic weapons). nuclear fission: Reaction that splits nuclei into less massive fragments.nuclear fusion: Reaction that joins the nuclei of atoms to form more massive nuclei. - (n.). The splitting of an atomic nucleus into two large fragments. nuclear fusion - (n.) ... ~ reactors naturally produce free neutron s; their role is to sustain the energy-producing chain reaction.
An atom contains protons and neutrons in its central nucleus. In fission, the nucleus splits, either through radioactive decay or because it has been bombarded by other subatomic particles known as neutrinos. The resulting pieces have less combined mass than the original nucleus, with the missing mass converted into nuclear energy. Controlled fission occurs when a neutrino bombards the nucleus of an atom, breaking it into two smaller, similarly-sized nuclei. Each newly freed neutron can go on to cause two separate reactions, each of which can cause at least two more.