[[Picture: D-t-fusion.png|250px|right|thumb|Die deuterium tritium fusion reaction is used as source of fast neutrons and can serve for the power production in a nuclear fusion reactor.]] Nuclear fusion designates a nuclear reaction, with which two atomic nuclei "merge" into a heavier core. In principle this reaction can be exothermic or endothermic; there are considerably large activation cross-sections (probability that between incident particle and another particle a certain reciprocal effect takes place) only with exotherms fusion reactions.

With the nuclear fusion the very strong Coulomb repulsive force between the positively charged cores is overcome. The tunnel effect more probably makes this procedure. In the distance from 10^ {- then the strong reciprocal effect binds the cores for 15} meters. Energy becomes free in the form of kinetic energy of the reaction products and in the form of radiation energy.

Energy balance

The energy hue is indicated to C by the Einstein mass suppl. IE equivalence formula E=m ". If the cores/particles developed with the fusion are easier than the output cores, the mass difference becomes free in the form of energy. Such fusion reactions are possible for exotherms only in the area of the light cores, since the binding energy per nucleon with rising mass number to approximately 60 increases. A strong local maximum has it with the nuclide Helium-4. The reactions most favorable for the fusion power production (see nuclear fusion reactor) to produce therefore it He-4. In the picture the one which can be most easily introduced of these reactions, D is represented above + to T - > 4He + n.

Nuclear fusion in Gestirnen

The nuclear fusion is the energy source of the stars, about our sun. Most stars fuse thereby with the hydrogen burning so mentioned hydrogen over several intermediate steps to helium, the temperature necessary for it lie with approx. 10 million Kelvin. At the end of its lifetime, if the hydrogen is used up, the energy comes from the fusion of helium or still heavier atomic nuclei. This fusion supplies less energy and needs a higher fusion temperature. Larger stars can produce a stronger gravitation pressure with their mass also, whereby these elements also heavier at the end fuse (up to the mass number of 60). Elements with larger mass numbers cannot develop however any longer in this way, since the fusion of the appropriate cores is endothermic. They are formed rather by neutron (s and r-process) and accumulation of proton (p-process).

Reactions (selection):

• {} ^3_1 \ mathrm {D} + {} ^2_1 \ mathrm {T} \ Rightarrow {} ^4_2 \ mathrm {H} + {} ^1_0 \ mathrm {n} + 17 {,} 588 MeV (largest activation cross-section)
• {} ^3_1 \ mathrm {D} + {} ^3_1 \ mathrm {D} \ Rightarrow {} ^3_2 \ mathrm {H} + {} ^1_0 \ mathrm {n} + 3 {,} 268 MeV
• {} ^3_1 \ mathrm {D} + {} ^3_1 \ mathrm {D} \ Rightarrow {} ^3_1 \ mathrm {T} + {} ^1_1 \ mathrm {p} + 4 {,} 03 MeV
• {} ^3_1 \ mathrm {T} + {} ^2_1 \ mathrm {D} \ Rightarrow {} ^4_2 \ mathrm {H} + {} ^1_1 \ mathrm {p} + 18 {,} 34 MeV

In the sun among other things the proton proton reaction takes place, a consequence of reactions, with which likewise Helium-4 with appropriate energy gain develops. Besides a carbon-catalyzed fusion cycle takes place, the Bethe-Weisaecker progressive reaction in the sun, which constitutes about 1.6% of the energy of the solar house stop.

The temperature necessary for the fusion depends among other things on the pressure. Since just as strong pressure cannot be produced as the gravitation pressure in the sun on earth, here the temperature necessary for the hydrogen fusion is with approximately 100 million Kelvin.

Applications

Physical research, neutron sources

Fusion reactions without nuclear chain reaction effect, i.e. without the reaction products by impacts to the fusion bring further cores, can be accomplished like other nuclear reactions by means of particle accelerators in the laboratory to physical research purposes. The deuterium tritium reaction specified above is used in such a way for the production of fast free neutrons. Also the Farnsworth deer Fusor is a source of free neutrons for research and technical purposes.

Weapons

Uncontrolled fusion nuclear chain reactions run off in nuclear weapons (hydrogen bomb). During conventional nuclear fission weapons (like the Hiroshima bomb Little Boy) an explosive yield of depending upon type about 15-60 kilotons TNT set, unfolded nuclear fusion weapons or H-bombs free of explosive yields up to approx. 57 megatons TNT (see Zar bomb). For the ignition of the fusion nuclear chain reaction inside a hydrogen bomb a Kernspaltungsbombe is platziert, in order to achieve a sufficient high temperature. Around the uranium bomb wasserstoffhaltige alloys are platziert, in which the fusion nuclear chain reaction takes place.

Peaceful power production

Large lines of development

For the use of the deuterium tritium reaction as energy source in international cooperation nuclear fusion reactors with magnetic inclusion of the plasma are developed (see ITER). Besides there are development programs for the fusion with inertia inclusion - said, an ignition of micro hydrogen bombs in a reactor container in rapid consequence simplifies by means of laser or ion beams (see also nuclear fusion reactor).

Cold fusion

Cold fusion different concepts and experiments are called, which describe fusion nuclear chain reactions, which run off at clearly smaller temperatures. Admits became this beginning particularly by the work of Martin meat man of 1989. The beginnings are however partly not reproducibly proven, partly stand the physical and technical possibility except doubt, however with negative or disputed total energy balance. In a set of laboratories they are nevertheless continued to examine.

Video

Literature

• Alexander M. Bradshaw, Thomas Hamacher: Nuclear fusion - a lasting energy source of the future. Scientific ones round-look 58 (12), P. 629 - 637 (2005), ISSN 0028-1050

See also

• Nuclear fusion reactor
  • Tokamak
    • Joint European torus (JET)
    • ASDEX Upgrade
    • International thermonuclear ones experimental reactor (ITER)
  • Stellarator
    • Wendelstein 7-AS
    • Wendelstein 7-X

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