Explain the process of controlled and uncontrolled chain reactions.

Explanation

(a) Controlled chain reaction
(i) In the controlled chain reaction the number of neutrons released is maintained to be one. This is achieved by absorbing the extra neutrons with a neutron absorber leaving only one neutron to produce further fission.
(ii) Thus, the reaction is sustained in a controlled manner. The energy released due to a controlled chain reaction can be utilized for constructive purposes.
(iii) Controlled chain reaction is used in a nuclear reactor to produce energy in a sustained and controlled manner.
Uncontrolled chain reaction
(i) In the uncontrolled chain reaction the number of neutrons multiplies indefinitely and causes fission in a large amount of the fissile material.
(ii) This results in the release of a huge amount of energy within a fraction of a second,
(iii) This kind of chain reaction is used in the atom bomb to produce an explosion