When two or more very light nuclei moving at very high speed are fused together to form a single nucleus, then the process is known as nuclear fusion. Let us discuss the complete phenomenon of nuclear fusion and solar energy.
Two deuterons can be fused together to form a tritium nucleus.
Then 1H3 can be further fused with deuteron to form He particle as:
Sun has been radiating energy at an enormous amount for billions of years. The process responsible for the solar energy is the fusion of light nuclei into heavier nuclei.
About 90% of the Solar mass is composed of H & He and rest 10% contains other elements mainly the lighter ones. The temperature of the interior of the sun is estimated to be about 2 × 107 K. At such a high temperature, the molecules dissociate into atoms and atoms are completely ionized to form a hot plasma.
Fusion of H nuclei into He nuclei is continuously taking place in this plasma, with the continuous liberation of energy.
In the solar condition, four H nuclei would fuse together directly to form a He nucleus. This may take place through a cycle of the process. Two of such cycles have been proposed the C cycle and proton-proton cycle.
i) Carbon Cycle: This cycle was proposed by Bethe in 1939 to account for the energy radiated by the sun. In this cycle, the fusion of H nuclei into He nuclei takes place in the sun through a series of nuclear reactions, in which C acts as a catalyst.
These reactions occur in the following order :
The net result in the fusion of 4 H nuclei into a He nucleus with the emission of two positions and 24.7 MeV of energy. The emitted positron combine with two electrons and are annihilates producing about 2 MeV of energy. Thus about 26.7 MeV of energy is released. For every He nucleus formed, an enormous number of such fusion can simultaneously take place in the sun.
ii) Proton-Proton Cycle :
Another possible cycle of reaction is a proton-proton cycle which occurs in the following sequence :
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