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 isotope of uranium with three fewer neutrons, 235 U, can much more readily be split apart than can 238 U; such an isotope is called fissile. When uranium splits (undergoes fission) it releases three neutrons that collide with other uranium atoms, thus creating a chain reaction. Some isotopes can be split too readily, so fast that a continuous fission reaction canât be maintained.