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Neutron

Characteristics

deuterons, nuclear fission reaction, electron volts, electrical forces, mass number

The atom consists of a small, massive, positively charged core (nucleus) surrounded by electrons (see Atom). The nucleus, containing most of the mass of the atom, is itself composed of neutrons and protons bound together by very strong nuclear forces, much greater than the electrical forces that bind the electrons to the nucleus. The mass number A of a nucleus is the number of nucleons, or protons and neutrons, it contains; the atomic number Z is the number of positively charged protons. A specific nucleus is designated as ?U. The expression ?U, for example, represents uranium-235. See Isotope.

The binding energy of a nucleus is a measure of how tightly its protons and neutrons are held together by the nuclear forces. The binding energy per nucleon, the energy required to remove one neutron or proton from a nucleus, is a function of the mass number A. The curve of binding energy implies that if two light nuclei near the left end of the curve coalesce to form a heavier nucleus, or if a heavy nucleus at the far right splits into two lighter ones, more tightly bound nuclei result, and energy will be released.

Nuclear energy, measured in millions of electron volts (MeV), is released by the fusion of two light nuclei, as when two heavy hydrogen nuclei, deuterons, combine in the reaction producing a helium-3 atom, a free neutron (Žn), and 3.2 MeV, or 5.1 x 10(-13) J (1.2 x 10(-13) cal). Nuclear energy is also released when the fission of a heavy nucleus such as ?U is induced by the absorption of a neutron producing cesium-140, rubidium-93, three neutrons, and 200 MeV, or 3.2 x 10(-11) J (7.7 x 10(-12) cal). A nuclear fission reaction releases 10 million times as much energy as is released in a typical chemical reaction.



Article key phrases:

deuterons, nuclear fission reaction, electron volts, electrical forces, mass number, nucleon, rubidium, MeV, nuclear forces, neutrons, Isotope, protons, uranium, Nuclear energy, left end, helium, electrons, atom, absorption, fusion, splits, expression, measure, core, example, function, times

 
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