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Explain nuclear fusion reaction with an example.

Answer»



Solution :Nuclear fusion. Nuclear fusion is process in which lighter nuclei (like `""_(1)H^(1)`) are fused together into heavier atom (like `""_(2)He^(4)`), with the release of enormous amount of energy. The energy thus RELEASED is known as thermonuclear energy and the reaction is called thermonuclear reaction. The cause of energy is again mass defect. Nuclear fusion takes place at very high temperature and very high density.
e.g. two deuterons can fuse together to form a medium nucleus and release energy of about 24 MeV.
i.e., `""_(1)H^(2)+""_(1)H^(2) rarr ""_(2)He^(4)+24` M eV.
Some other EXAMPLES of such REACTIONS are
`""_(1)H^(1)+""_(1)H^(1) rarr ""_(1)H^(2)+""_(+1)e^(0)+0.42` M eV
`4""_(1)H^(1) rarr ""_(1)He^(4)+2""_(+1)e^(0)+26.7` M eV
`""_(1)H^(3)+""_(1)H^(2) rarr ""_(2)He^(4)+""_(0)n^(1)+17.6` M eV
`""_(4)Li^(7)+""_(1)H^(1) rarr ""_(2)He^(4)+""_(2)He^(4)+17.3` M eV.
Nuclear fusion reaction takes place in the PRESENCE of very high temperature ( about `10^(7)` K), so they are called thermonuclear reactions. All these reactions are exoergic and release huge energies. The energy come from conversion of mass of final stage nucleus formed as a result of fusion is always less than that of the indiyidual light nuclei.
The temperature of the order of `10^(7)` K is very difficult to obtain. The mechanism involved for producing high temperature is a self-sustained fission explosion. When an atom bomb containing `U^(235)` explodes, very high temperature `( ~= 10^(7)K)` is produced. Thus atomic explosion acts as trigger and release tremendousamount of energy.
Conditions for Fusion
(1) Either the reacting nuclei should be given large amount of kinetic energy to overcome the mutual repulsion between them.
(2) Or a very higher temperature should be produced. Such high temperature exists in the territoryof stars. Therefore, thermal fission is possible in stars.
Example
Nuclear fusion takes place in sun and stars. Hence they emit a Jarge amount of energy.
Use
Nuclear fusion is used in hydrogen bomb.


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