Question

5. How many “average” collisions with hydrogen nuclei would a 1 MeV neutron need to undergo before it becomes a "slow" neutron?

Answer 1

m: the mass of neutron; M : the mass of nuclei; v/v': initial/final velocity of the neutron

Conservation of energy and momentum

Rearranging the equations will yield,

i.e. neutron energy after a collision is between E and E'.

Probability of a neutron of energy E becoming of energy E' after a collision is,

With this probability, we can now calculate the average energy after one collision,

For the given case in question, .

Let us take the final energy of neutron to be 0.001eV, which gives,

Hope this clarifies your doubt.

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