JEE Main & Advanced Physics Nuclear Physics And Radioactivity Nuclear Fusion

(1) In nuclear fusion two or more than two lighter nuclei combine to form a single heavy nucleus. The mass of single nucleus so formed is less than the sum of the masses of parent nuclei. This difference in mass results in the release of tremendous amount of energy

(2) For fusion high pressure (\[\approx {{10}^{6}}\] atm) and high temperature (of the order of \[{{10}^{7}}\,K\] to \[{{10}^{8}}\,K\]) is required and so the reaction is called thermonuclear reaction.

(3) Here are three examples of energy-liberating fusion reactions, written in terms of the neutral atoms. Together the reactions make up the process called the proton-proton chain.

\[_{1}^{1}H+\,_{1}^{1}H\to \,_{1}^{2}H+{{\beta }^{+}}+{{\nu }_{e}}\] \[_{1}^{2}H+\,_{1}^{1}H\to \,_{2}^{3}He+\gamma \]

\[\frac{_{2}^{3}He+\,_{2}^{3}He\to \,_{2}^{4}He+\,_{1}^{1}H\,+\,_{1}^{1}H}{4{{\,}_{1}}{{H}^{1}}{{\to }_{2}}H{{e}^{4}}+2\,{{\beta }^{+}}+2\gamma +26.73\,MeV}\]

(4) The proton-proton chain takes place in the interior of the sun and other stars. Each gram of the suns mass contains about \[4.5\times {{10}^{23}}\]  protons. If all of these protons were fused into helium, the energy released would be about 130,000 kWh. If the sun were to continue to radiate at its present rate, it would take about \[75\times {{10}^{9}}\,years\] to exhaust its supply of protons.

(5) For the same mass of the fuel, the energy released in fusion is much larger than in fission.

(6) Plasma : The temperature of the order of \[{{10}^{8}}\,K\] required for thermonuclear reactions leads to the complete ionisation of the atom of light elements. The combination of base nuclei and electron cloud is called plasma. The enormous gravitational field of the sun confines the plasma in the interior of the sun.

The main problem to carryout nuclear fusion in the laboratory is to contain the plasma at a temperature of \[{{10}^{8}}\,K\]. No solid container can tolerate this much temperature. If this problem of containing plasma is solved, then the large quantity of deuterium present in sea water would be able to serve as in-exhaustible source of energy.

Nuclear bomb (Based on uncontrolled nuclear reactions)