CBSE NOTES CLASS 12 PHYSICS
CHAPTER 13 NUCLEUS
When light nuclei fuse into a heavier nucleus it is called fusion. Energy in stars is due to fusion.
For fusion to take place, the two nuclei must come close enough so that attractive short-range nuclear force is able to affect them. However, since they are both positively charged particles, they experience coulomb repulsion. They, therefore, must have enough energy to overcome this coulomb barrier. The height of the barrier depends on the charges and radii of the two interacting nuclei.
The temperature at which two protons in a proton gas would (on an average) have enough energy to overcome the coulomb barrier:
(3/2)kT = KE ≈ 400 keV, which gives T ~ 3 × 109 K.
When fusion is achieved by raising the temperature of the system so that particles have enough kinetic energy to overcome the coulomb repulsive behaviour, it is called thermonuclear fusion.