It is a process of formation of heavier and bigger nucleus by the combination of various lighter and smaller nucleus. This process is called nuclear fusion.
This process can take place by falling of highly accelerated protons and deuterons in the nuclei of lighter elements. These processes occur at very reasonable rate and at very high temperature ranges. Therefore, these processes are also called thermonuclear processes. Once nuclear fusion process is initiated, the amount of energy released is sufficient to maintain the temperature and to keep the process going.
6C12 + 1H1 ———–> 7N13 + Q
Where Q denotes the amount of energy released during the process.
