What is Nuclear Fusion
The conventional energy sources like coal or petroleum releases energy through chemical reactions and the energy released are of the order of electron volts per atom. However, energy involved in nuclear processes are million times larger in MeVs per nucleon which means for the same quantity of matter the nuclear mass will give million times more energy than the conventional source. The sources of nuclear energy is by two methods 1) nuclear fission in which the energy is released due to breakdown of the nucleus and 2) nuclear fusion in which two nuclei fuse to form a new element.
Energy is released when two light nuclei combine to form a larger nucleus and the process is called as nuclear fusion. Some examples of such energy liberating reactions are
1 1 2
1H+ 1H→ 1H + e+ + ν + 0.42 MeV (1)
2 2 3
1H+ 1H→2He + n + 3.27 MeV (2)
2 2 3 1
1 H + H → 1H + 1H + 4.03 MeV (3)
In reaction 1, two protons combine together to form a deuteron and a positron and release an energy of 0.42 MeV. Similarly in reaction (2), two hydrogen atom fuse together to form a light isotope of helium. In reaction 3, two deuteron combine to form a triton and a proton. All the above fusion reaction involves fusion of two lighter nuclei to form a larger nucleus with release of enormous amount of energy. The nuclear fusion reaction is hindered by Coulomb repulsion which prevents two positively charged nuclei from fusing. The height of this Coulomb barrier depends on the height of the radii of the two interacting nuclei. The temperature at which the proton is a proton gas gives enough energy to overcome the coulomb’s barrier.
Bulk matter must be used to produce nuclear fusion to generate useful amount of energy. The temperature of the material is increased so much that the particles have enough energy through their thermal motion to overcome the coulomb barrier and is known as thermonuclear fusion. However, for thermonuclear fusion to happen extreme conditions of temperature and pressure is required which is present only in the stars including Sun. Thus, the energy generation in stars takes place via thermonuclear fusion.
Eniwetok Atoll is the place at which the first thermonuclear reaction on Earth occurred on November 1, 1952. On this day USA exploded a fusion device, which generated energy equivalent to 10 million tons of TNT (1 ton of TNT releases 2.6 x 1022 MeV of energy). Since fusion reactors are the future power source, it is being pursued vigorously in many countries
In fusion, lighter nuclei combine to form a larger nucleus. Fusion of hydrogen nuclei into helium nuclei is the source of energy of all stars including our sun. It is now possible to create thermonuclear fusion in controlled nuclear reactors to produce energy.