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Explain what are nuclear fission and fusion giving an example of each. Write down the formulae for energy generated in each of these processes. - Physics

Answer in Brief

Explain what are nuclear fission and fusion giving an example of each. Write down the formulae for energy generated in each of these processes.

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Solution

Nuclear fission is a nuclear reaction in which a heavy nucleus of an atom, such as that of uranium, splits into two or more fragments of comparable size, either spontaneously or as a result of bombardment of a neutron on the nucleus (induced fission). It is followed by the emission of two or three neutrons. The mass of the original nucleus is more than the sum of the masses of the fragments. This mass difference is released as energy, which can be enormous as in the fission of 235U.

Nuclear fission was discovered by Lise Meitner, Otto Frisch, Otto Hahn and Fritz Strassmann in 1938.

The products of the fission of 235U by thermal neutrons are not unique. A variety of fission fragments are produced with mass number A ranging from about 72 to about 138, subject to the conservation of mass-energy, momentum, number of protons (Z) and number of neutrons (N}. A few typical fission equations are

(1) \[\ce{_92^235U + _0^1n-> _92^236U -> _54^140Xe + _38^94Sr + 2 _0^1n + 200 MeV}\]

(235 + 1 = 236 = 140 + 94 + 2)

(2) \[\ce{_92^235U + _0^1n-> _92^236U -> _56^144Ba + _36^90Kr + 2 _0^1n + 200 MeV}\]

(235 + 1 = 236 = 144 + 90 + 2)

(3) \[\ce{_92^235U + _0^1n-> _92^236U -> _57^148La + _35^85Br + 3 _0^1n + 200 MeV}\]

(235 + 1 = 236 = 148 + 85 + 3)

A type of nuclear reaction in which lighter ato c nuclei (of low atomic number) fuse to form a heavier nucleus (of higher atomic number) with the release of enormous amount of energy is called nuclear fusion.

Very high temperatures, of about 107 K to 108 K, are required to carry out nuclear fusion. Hence, such a reaction is also called a thermonuclear reaction.

Example: The D-T reaction, being used in experimental fusion reactors, fuses a deuteron and triton nuclei at temperatures of about 108 K.

\[\ce{\underset{\text{(deuteron)}}{_1^2D} + \underset{\text{(triton)}}{_1^3T}->\underset{\text{(helium nucleus)}}{_2^4He} + \underset{\text{(neutron)}}{_0^1n} + 17.6 MeV}\]

Concept: Nuclear Energy
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Balbharati Physics 12th Standard HSC Maharashtra State Board
Chapter 15 Structure of Atoms and Nuclei
Exercises | Q 8 | Page 342
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