To generate useful amount of energy, nuclear fusion must occur in bulk matter. What is needed is to raise the temperature of the material until the particles have enough energy due to their thermal motions alone to penetrate the coulomb barrier. This process is called thermonuclear fusion.Thus, for thermonuclear fusion to take place, extreme conditions of temperature and pressure are required, which are available only in the interiors of stars including sun.
Energy generation in stars
Nuclear fusion is the principal source of energy in stars and fusion can happen if each nucleus has sufficient kinetic energy to enable them to overcome their mutual repulsion, be captured by the strong nuclear force and stick together. In star formation,the kinetic energy to do this, comes from the conversion of gravitational energy into thermal energy by the Kelvin Helmholtz contraction. In the case of stars like the sun, fusion can occur when the temperature of the contracting cloud reaches about 8×106K. It is fusion of hydrogen nuclei by thermonuclear fusion reactions with a release of binding energy that is the primary source of energy generation in stars.
Energy generation in sun
The fusion reaction in the sun is a multi-step process in which hydrogen is burned into helium, hydrogen being the fuel and helium the ashes. The proton-proton (p, p) cycle by which this occurs is represented by the following sets of reactions:
For the fourth reaction to occur, the first three reactions must occur twice, in which case two light helium nuclei unite to form ordinary helium or nucleus. If we consider the combination 2(1) + 2(3) + 2(3) +(4), the net effect is 411H+2e−→24He+2ν+6γ+26.7MeV
Examples of Nuclear Fusion Reactions
Nuclear fusion is a process when two or more nuclei combine to form a large nuclei and release some energy. These are the examples of Nuclear Fusion Reaction: