Monday 19 September 2011

THERMONUCLEAR FUSION IN SUN AND OTHER STARS


Just as energy is released in nuclear fission, it is also released when light nuclei like proton and deuteron fuse together at a very high temperature to form helium nucleus. Such a process is called thermonuclear fusion.

Hydrogen works as fuel and helium is the end product of the process, called proton-proton cycle, occurring in the Sun. The reactions are given by
1H1 + 1H1 ® 1H2 + e  + n + 0.42 MeV                                   ( 1 )

e+ + e- ® 2 g + 1.02 MeV                                                   ( 2 )
1H2 1H1 ® 2He3 + g + 5.49 MeV                                          ( 3 )
2He3 + 2He3 ® 2He4 + 1H1 + 1H1 + 12.86 MeV                     ( 4 )
The first three reactions should occur twice so that the fourth reaction becomes possible. The 
total energy released in this process is = 2 ´ ( 0.42 + 1.02 + 5.49 ) + 12.86 = 26.7 MeV. 
Carbon-nitrogen cycle is also proposed in case of the Sun in which 25 MeV energy is
released and the net reaction is fusion of 4 protons forming 1 nucleus of helium, 2He4.

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