1. A type of nuclear reaction in which atomic nuclei of low atomic number fuse to form a heavier nucleus with the release of large amounts of energy. In nuclear fission reactions a neutron is used to break up a large nucleus, but in nuclear fusion the two reacting nuclei themselves have to be brought into collision. As both nuclei are positively charged there is a strong repulsive force between them, which can only be overcome if the reacting nuclei have very high kinetic energies. These high kinetic energies imply temperatures of the order of 108 K. As the kinetic energy required increases with the nuclear charge (i.e. atomic number), reactions involving low-atomic-number nuclei are the easiest to produce. At these elevated temperatures, however, fusion reactions are self-sustaining; the reactants at these temperatures are in the form of a plasma (i.e. nuclei and free electrons) with the nuclei possessing sufficient energy to overcome electrostatic repulsion forces. The fusion bomb (see nuclear weapons) and the stars generate energy in this way. It is hoped that the method will be harnessed in the thermonuclear reactor as a source of energy for human use. A great deal of effort has been devoted to this but considerable difficulties remain.
Typical fusion reactions with the energy release in joules are:
By comparison, the formation of a water molecule from hydrogen and oxygen is accompanied by the release of 1.5×10−19 J.
A large amount of work is currently being done on cold fusion, i.e. fusion that can occur at lower temperatures than those necessary to overcome the electrostatic repulsion between nuclei. The most productive approach is muon-catalysed fusion, in which the deuterium atoms have their electrons replaced by negative muons to give ‘muonic atoms’ of deuterium. The muon is 207 times heavier than the electron, so the muonic deuterium atom is much smaller and is able to approach another deuterium atom more closely, allowing nuclear fusion to occur. The muon is released to form another muonic atom, and the process continues. The limiting factor is the short lifetime of the muon, which restricts the number of fusion reactions it can catalyse.
2. The production of new transactinide elements by bombarding nuclei of one element with nuclei of another element at an energy precisely chosen to allow the fusion reaction to occur.
Nuclear fusion. Tritium–deuterium reaction.
http://www.chemteam.info/Chem-History/Rutherford-1934b/Rutherford-1934b.html Rutherford’s 1934 paper in Proceedings of the Royal Society
The fusing together of two atomic nuclei of low atomic number to form a nucleus of higher atomic number, with the release of energy (e.g. hydrogen to helium). Nuclei are positively charged, so high kinetic energies are required to overcome the mutual repulsive forces; this implies temperatures of the order of 108 K. Nuclear fusion takes place inside stars and is the process by which energy is released that makes the star shine. See also carbon–nitrogen cycle; proton–proton reaction; triple-alpha process.
A nuclear reaction in which two nuclei, each of which has a low atomic number, combine to form a heavier nucleus, with the emission of a great deal of energy. The nucleosynthesis of many chemical elements occurs by nuclear fusion, which is the process that powers the stars. Because atomic nuclei are positively charged, it is necessary to have very high kinetic energies for nuclear fusion to occur, although the energy to overcome the repulsive electrostatic barrier is not as high as might be supposed from classical physics because of the quantum-mechanical tunnel effect through the barrier.
See fusion.
- tuya
- TVC
- T violation
- TWA
- TWAIN
- twang
- Twardowski, Kazimierz (1866–1938)
- Tweed Ring
- tweening
- blocking anticyclone
- blocking capacitor
- blocking factor
- blocking high
- blocking oscillator
- blocking software
- blocking temperature
- blocking volume
- block kriging
- block length
- block mountain
- block multiplication
- block retrieval
- block-structured languages
- block universe theory of time
- block valve