Write a note nuclear fission chain reaction.

Explanation

Nuclear fission is the phenomenon in which a heavy nucleus breaks up into lighter nuclei of nearly equal masses with liberation of energy
e.g. : When `._(92)U^(235)` is bombarded by a neutron an isotope of uranium is formed which further breaks up into Xenon and Strontium.
`._(92)U^(235)+_(0) n^(1) rarr_(92)U^(236) rarr_(54) Xe^(140)+_(38) Sr^(94)+2_(0)n^(1)+`energy
In the above relation a mass defect of 0.216 amu occurs. This is equivalent to energy released of the order 200 MeV.
The products of fission are not unique `._(92)U^(236)` many also undergo fission splitting into `._(56)Ba^(141) and ._(36)Kr^(92)`. The reaction is represented by
`._(92)U^(235)+_(0)n^(1) rarr_(92)U^(236) rarr_(56) Ba^(141) +_(36)Kr^(92)+3_(0)n^(1)+` energy
The energy released usually appears in the form of K.E. of fission fragments and neutrons. Some of the energy is also released in the form of `gamma ` rays, heat energy and light energy. The fission, temperature and pressure become very high . Further, the fission fragments are usually radioactive and they become stable by emitting `alpha` rays and `beta` rays.