# Nuclear Fusion Nuclear fusion is a process in which two or more light atomic nuclei combine to form a heavier nucleus, releasing a large amount of energy in the form of heat. This is the reaction that powers the Sun and all stars in the universe. When light atomic nuclei are forced together under extreme conditions, they fuse into a single heavier nucleus and release tremendous energy. This section explains how nuclear fusion works, why it releases so much energy, and why it is considered a potential clean energy source. ## Definition of Nuclear Fusion Nuclear fusion is a process where two or more light atomic nuclei combine to form a heavier nucleus, releasing a large amount of energy in the form of heat. ## Natural Occurrence Nuclear fusion occurs naturally in stars such as the Sun, where extremely high temperatures and pressures cause nuclei to collide and fuse. Scientists are actively researching nuclear fusion as a potential clean and sustainable source of energy. ## Reason for Fusion The tendency of small nuclei to undergo fusion rather than fission is explained by binding energy: - Small nuclei have a low binding energy per nucleon, making them less stable. - They tend to fuse to form heavier nuclei that have a higher binding energy per nucleon, moving towards a region of greater stability. - The binding energy per nucleon increases with mass number, reaching a maximum for $^{56}\mathrm{Fe}$ (atomic mass $A = 56$), which is 8.8 MeV per nucleon. - This initial increase in binding energy per nucleon favors fusion reactions for light nuclei. ## Energy Release in Nuclear Fusion Energy is released in nuclear fusion because the total mass of the products is less than the total mass of the reactants. This mass defect is converted into energy according to Einstein's mass-energy equivalence equation: $$E = \Delta m c^2$$ ### Example Calculation for Deuterium-Tritium Fusion **Reactants (Deuterium + Tritium):** - Mass of Deuterium = $2.014102\ \mathrm{u}$ - Mass of Tritium = $3.016049\ \mathrm{u}$ - Total Mass (L.H.S.) = $5.030151\ \mathrm{u}$ - Total Mass in kg = $5.030151\ \mathrm{u} \times 1.660 \times 10^{-27}\ \mathrm{kg/u} = 8.350 \times 10^{-27}\ \mathrm{kg}$ - Energy (L.H.S.) = $8.350 \times 10^{-27}\ \mathrm{kg} \times (3 \times 10^{8}\ \mathrm{ms}^{-1})^2 = 7.515 \times 10^{-10}\ \mathrm{J} = 4696.87\ \mathrm{MeV}$ **Products (Helium + Neutron):** - Mass of Helium = $4.002603\ \mathrm{u}$ - Mass of Neutron = $1.008665\ \mathrm{u}$ - Total Mass (R.H.S.) = $5.011268\ \mathrm{u}$ - Total Mass in kg = $5.011268\ \mathrm{u} \times 1.660 \times 10^{-27}\ \mathrm{kg/u} = 8.319 \times 10^{-27}\ \mathrm{kg}$ - Energy (R.H.S.) = $8.319 \times 10^{-27}\ \mathrm{kg} \times (3 \times 10^{8}\ \mathrm{ms}^{-1})^2 = 7.4871 \times 10^{-10}\ \mathrm{J} = 4679.438\ \mathrm{MeV}$ **Energy Released (Q):** $$Q = \text{Energy (L.H.S.)} - \text{Energy (R.H.S.)} = 4696.87\ \mathrm{MeV} - 4679.438\ \mathrm{MeV} = 17.43\ \mathrm{MeV}$$ A positive value of Q indicates an exothermic reaction, meaning energy is released. A single event of deuterium and tritium fusion releases 17.43 MeV of energy.