Question
Explain the process of thermonuclear fusion with example.
✓
Answer
$\rightarrow$ When two light nuclei fuse to form a larger nucleus, energy is released, because binding energy increases during the process.
$\rightarrow$ Some examples of such energy liberating nuclear fusion reactions are :
${ }_1 H ^1+{ }_1 H ^1 \rightarrow{ }_1 H ^2+e^{+}+v+0.42 MeV$
${ }_1 H ^2+{ }_1 H ^2 \rightarrow{ }_2 He ^3+n+3.27 MeV$
${ }_1 H ^2+{ }_1 H ^2 \rightarrow{ }_1 H ^3+{ }_1 H ^1+4.03 MeV$
$\rightarrow$ In the first reaction, two protons combine to form a deuteron and a positron with a release of $0.42 MeV$ energy.
$\rightarrow$ In the second reaction, two deuterons combine to form the isotope of helium ${ }_2 He ^3$.
$\rightarrow$ In third reaction two deuterons combine to form a tritium and a proton. $4.03 MeV$ energy is released during this process.
$\rightarrow$ For a fusion to take place, the two nuclei must come close enough so that nuclear force is able to affect them.
$\rightarrow$ This force must be strong enough to overcome the repulsive barrier between two positively charged nuclei.
$\rightarrow$ The height of the barrier depends on the charges and radii of the two interacting nuclei.
$\rightarrow$ For example :
The barrier height for two protons is $\sim 400 keV$.
The temperature required for a proton to overcome this barrier is $T$ .
$\therefore \frac{3}{2} k T =400 keV$
$T =\frac{2 \times 400 \times 10^3 \times 1.6 \times 10^{-19}}{3 \times 1.38 \times 10^{-23}}$
$T =3 \times 10^9 K$
$\rightarrow$ When fusion is achieved by raising the temperature of the system so that particles have enough kinetic energy to overcome the Coulomb repulsive barrier, it is called thermo $-$ nuclear fusion.
$\rightarrow$ Some examples of such energy liberating nuclear fusion reactions are :
${ }_1 H ^1+{ }_1 H ^1 \rightarrow{ }_1 H ^2+e^{+}+v+0.42 MeV$
${ }_1 H ^2+{ }_1 H ^2 \rightarrow{ }_2 He ^3+n+3.27 MeV$
${ }_1 H ^2+{ }_1 H ^2 \rightarrow{ }_1 H ^3+{ }_1 H ^1+4.03 MeV$
$\rightarrow$ In the first reaction, two protons combine to form a deuteron and a positron with a release of $0.42 MeV$ energy.
$\rightarrow$ In the second reaction, two deuterons combine to form the isotope of helium ${ }_2 He ^3$.
$\rightarrow$ In third reaction two deuterons combine to form a tritium and a proton. $4.03 MeV$ energy is released during this process.
$\rightarrow$ For a fusion to take place, the two nuclei must come close enough so that nuclear force is able to affect them.
$\rightarrow$ This force must be strong enough to overcome the repulsive barrier between two positively charged nuclei.
$\rightarrow$ The height of the barrier depends on the charges and radii of the two interacting nuclei.
$\rightarrow$ For example :
The barrier height for two protons is $\sim 400 keV$.
The temperature required for a proton to overcome this barrier is $T$ .
$\therefore \frac{3}{2} k T =400 keV$
$T =\frac{2 \times 400 \times 10^3 \times 1.6 \times 10^{-19}}{3 \times 1.38 \times 10^{-23}}$
$T =3 \times 10^9 K$
$\rightarrow$ When fusion is achieved by raising the temperature of the system so that particles have enough kinetic energy to overcome the Coulomb repulsive barrier, it is called thermo $-$ nuclear fusion.
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