Theory:

In \(1939\), German scientists Otto Hahn and F. Strassman discovered the process of nuclear fission. When a uranium nucleus is bombarded with a neutron, it splits up into two smaller nuclei of equivalent mass, emitting a few neutrons and some amount of energy.
 
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Nuclear fission
Nuclear fission is the process of splitting or breaking up a heavy nucleus into two smaller nuclei with the release of a huge quantity of energy and a few neutrons.
Example:
Nuclear fission of a uranium nucleus (\(U^{235}\))
 
uranium fission.png
Splitting of a uranium nucleus
 
\(_{92}U^{235}\) \(+\) \(_{0}n^{1}\) \(\rightarrow\) \(_{56}Ba^{141}\) \(+\) \(_{36}Kr^{92}\) \(+\) \(3\) \(_{0}n^{1}\) \(+\) \(Q\) (\(energy\))
The average energy released in each process of nuclear fission is about \(3.2 \times{10^{-11}}\) \(J\).
 
Features of fission reaction:
Some of the salient features of a fission reaction are
  1. A fission reaction occurs if the nucleus of a heavy atom (\(U\ -235\)) is bombarded with a slow-moving neutron.
  2. Fast-moving neutrons cannot produce a fission reaction.
  3. The products of a fission reaction are a lighter nucleus of atomic mass ranging from \(85\) to \(104\), a heavy nucleus of atomic mass ranging from \(130\) and \(149\) with two or three neutrons.
  4. Fission reaction is accompanied by the release of an enormous amount of energy in the form of light and heat.
  5. Sometimes, fission reaction produces \(γ\)-radiations of a very shorter wavelength.
Reference:
https://commons.wikimedia.org/wiki/File:Liquid_drop_model_of_nuclear_fission.jpg
https://commons.wikimedia.org/wiki/File:CNX_Chem_21_04_Fission1.png