Nuclear Fusion:
When two light nuclei fuse together to form a large nucleus and energy is released, then the process is called nuclear fusion. The mass of the nucleus obtained from the fusion is less than the sum of the masses of the nuclei that fuse so, the loss in mass of the nucleus is transformed in the form of energy in accordance with the mass-energy equation. We have cleared this fact in the section of binding energy per nucleons.
Nuclear fusion is a complex process. For fusion, it in important to bring the nuclei to be fused so close that that these are in the range of nuclear forces, which is a difficult task. When nuclei are brought close, then the acting Coulomb repulsive force is strong. To overcome this Coulomb force, the kinetic energy of the nuclei should be in the range of 0.1 MeV to 1 MeV. These energies can be obtained from particle accelerators but in accelerators, the possibility of radiating is more for nucleus than fusion. Also, to collide a nucleus with another, the energy invested in accelerator is more as compared to the energy obtained from fusion. To obtain energy from fusion, the matter particles in the gaseous form are heated at high temperature so that the nuclei come so close that fusion occurs. This temperature is in the range of 109K and this type of fusion reaction is called thermonuclear fusion.
An example of fusion reactions is shown below in the form of fusion of deuterium nuclei:
Thus three nuclei of deuterium combine to form a nucleus of Helium \((\frac{4}{2})He\) nucleus and 21.6 MeV energy is released. Although the energy obtained from fusion (21.6 MeV) is quite less than the fission of a Uranium nucleus (200 MeV), but if we compare the fusion energy of deuterium per kilogram to fission energy of Uranium per kilogram, then it is very low. Also, no radioactive products are formed in fusion whereas the products in fission are radioactive. Thus, comparatively, fusion energy is a clean source.
