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Explain giving necessary reactions, how energy is released during (i) fission, and (ii) fusion. |
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Answer» SOLUTION :(i) In a fission process Uranium-235 nucleus BREAKS into two nearly equal fragments releasing great amount of ENERGY when bombarded by a slow moving (thermal) neutron. The representative reaction is `" "_(0)^(1)n + " "_(92)^(235)U to (" "_(92)^(236)U) to " "_(56)^(144)Ba + " "_(36)^(89)kr + 3" "_(0)^(1)n + Q` The energy released (the Q-value) in the fission reaction is of the order of 200 MeV per fissioning nucleus. This is estimated as follows : Let us take a nucleus with mass number A = 240 breaking into two fragments each of A = 120. Then binding energy per nucleon for A = 240 is about 7.6 MeV but that for the two A = 120 fragments is about 8.5 MeV. `therefore` Gain in binding energy per nucleon is about 0.9 MeV and hence the total gain in binding energy is `240 xx 0.9` or 216 MeV. (ii) In fusion reaction four hydrogen nuclei fuse together to form a helium nucleus along with release of about 26.7 MeV of energy. The actual reactions is quite complex and takes place in four STAGES but the combined effect of all these stages may be written in the form of following reaction : `4" "_(1)^(1)H +2e^(-) =" "_(2)^(4)He + 2nu + 6gamma + 26.7 MeV` The binding energy curve again helps in explaining the cause of energy generation in fusion reaction. Binding energy per nucleon of `" "_(2)^(4)He` is about 6.7 MeV but binding energy of hydrogen is zero. As a result, gain in binding energy on fusion is `4xx6.7=26.8MeV`. |
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