Nuclear binding energy in experimental physics is the minimum energy that is required to disassemble the nucleus of an atom into its constituent protons and neutrons, known collectively as nucleons. The binding energy for stable nuclei is always a positive number, as the nucleus must gain energy for the nucleons to move apart from each other.
Nucleons are attracted to each other by the strong nuclear force. In theoretical nuclear physics, the nuclear binding energy is considered a negative number. In this context it represents the energy of the nucleus relative to the energy of the constituent nucleons when they are infinitely far apart.
Both the experimental and theoretical views are equivalent, with slightly different emphasis on what the binding energy means. The mass of an atomic nucleus is less than the sum of the individual masses of the free constituent protons and neutrons.
This 'missing mass' is known as the mass defect, and represents the energy that was released when the nucleus was formed. The term "nuclear binding energy" may also refer to the energy balance in processes in which the nucleus splits into fragments composed of more than one nucleon.
If new binding energy is available when light nuclei fuse nuclear fusionor when heavy nuclei split nuclear fissioneither process can result in release of this binding energy. This energy may be made available as nuclear energy and can be used to produce electricity, as in nuclear poweror in a nuclear weapon.
When a large nucleus splits into pieces, excess energy is emitted as gamma rays and the kinetic energy of various ejected particles nuclear fission products. These nuclear binding energies and forces are on the order of one million times greater than the electron binding energies of light atoms like hydrogen.
An absorption or release of nuclear energy occurs in nuclear reactions or radioactive decay ; those that absorb energy are called endothermic reactions and those that release energy are exothermic reactions. Energy is consumed or released because of har uran hög eller låg massdefekt in the nuclear binding energy between the incoming and outgoing products of the nuclear transmutation.
The best-known classes of exothermic nuclear transmutations are nuclear fission and nuclear fusion. Nuclear energy may be released by fission, when heavy atomic nuclei like uranium and plutonium are broken apart into lighter nuclei. The energy from fission is used to generate electric power in hundreds of locations worldwide.
Nuclear energy is also released during fusion, when light nuclei like hydrogen are combined to form heavier nuclei such as helium. The Sun and other stars use nuclear fusion to generate thermal energy which is later radiated from the surface, a type of stellar nucleosynthesis.
In any exothermic nuclear process, nuclear mass might ultimately be converted to thermal energy, emitted as heat. In order to quantify the energy released or absorbed in any nuclear transmutation, one must know the nuclear binding energies of the nuclear components involved in the transmutation.
Electrons and nuclei are kept together by electrostatic attraction negative attracts positive. Furthermore, electrons are sometimes shared by neighboring atoms or transferred to them by processes of quantum physics ; this link between atoms is referred to as a chemical bond and is responsible for the formation of all chemical compounds.
The electric force does not hold nuclei together, because all protons carry a positive charge and repel each other. If two protons were touching, their repulsion force would be almost 40 Newton. Because each of the neutrons carries total charge zero, a proton could electrically attract a neutron if the proton could induce the neutron to become electrically polarized.
Higher multipoles, needed to satisfy more protons, cause weaker attraction, and quickly become implausible.