AIIMS 2011 Physics Nuclear Fission Assertion Reason Question
Assertion : It is desirable to slow down fast moving neutrons to sustain controlled chain reactions. Reason : Slow moving neutrons efficiently collides with U²³⁵.
Both assertion and reason are true and reason is the correct explanation of assertion
Both assertion and reason are true but reason is not the correct explanation of assertion
Assertion is true but reason is false
Both assertion and reason are false
Correct Answer
Detailed Explanation
The average energy of a neutron produced in fission of U235 is 2 MeV. These neutrons unless slowed down will escape from the reactor without interacting with uranium nuclei, unless a large amount of fissionable material is used for sustaining the chain reaction. What we needs to do is to slow down the fast neutrons by elastic scattering with light nuclei. Chadwick's experiment showed that in an elastic collision with hydrogen neutron almost come to rest.
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