Nuclear Fission and Fusion





Nuclear fission and fusion

The nuclear fission may be defined as the splitting of a heavy nucleus into nearly two equal parts by the bombardment of slow neutron with the release of energy. Otton Hahn and Strassmann (1939) carried out first nuclear fission reaction as:

 

Nuclear fission and fusion

In this process the emitting neutrons bombard again on ^{235}_{92}U and a chain reaction may be set up. In this way a huge amount of energy is liberated. This process is used in atom bomb and in atomic reactors.

The process in which lighter nuclei fuse together to produce heavier nucleus is called nuclear fusion.

e.g.

^2_1H + ^2_1H \to ^4_2He + ^1_0n + 17.6 Mev \\ ^7_3Li + ^1_1H \to2 ^4_2He + 17.6 MeV \\ ^6_3Li + ^2_1H \to 2 ^4_2He + 22.4 MeV \\ ^2_1H + ^2_1H \to ^4_2He + 24.9 Mev

 

Since in these processes, energy is to be given to the bombarding particle to overcome the repulsion between the target and bombarding particle, hence such reactions are also known as thermo nuclear reactions. Such reactions are used in hydrogen bomb. Such type of reactions are responsible for the luminosity of stars and source of energy in the sun.

Such reactions are possible when temp is > 10^6K. Bethe (1939) proposed ‘Carbon-Nitrogen Cycle’ for the energy source of stars including the sun. the cule is as follow

^{12}_6C + ^1_1H \to ^{13}_7N + \gamma \\ ^{13}_7N \to ^{13}_6C + ^0_{+1}e \\ ^{13}_6C + 61_1H \to ^{14}_7N + \gamma \\ ^{14}_7N + ^1_1H \to ^{15}_8O \gamma \\ ^{15}_8O \to ^{15}_7N + ^0_{+1}e\\ \line(1,0){250}\\ ^{15}_7N + ^1_1H \to ^{12}_6C + ^4_2He \\ \line(1,0){250}\\ 4 ^1_1H \to ^4_2He + 2 _{+1}^0e + 26 MeV

 

But according to modern view, proton-proton interaction leading to helium takes place as follows

^1_1H + ^1_1H \to ^2_1H + ^0_{+1}e \\ ^2_1H + ^1_1H \to ^3_2He + \gamma \\ ^3_2He + ^1_1H \to ^1_1He + \gamma \\ \line(1,0){250} \\ 4 ^1_1H \to ^4_2He + 2 ^0_{+1}e + 24.7 MeV \\ \line(1,0){250}

 

Spallation: according to Seaborg a nucleus can be splitted into several nuclei when hit by a high energy charged particles like _1H^2 of 200 MeV energy. Here (10 – 20) neutrons are emitted.

^{75}_{33}As + _1H^2 \to ^{56}_{25}Mn + 9 _1H^1 + 12_0 n^1

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