If a 2.0-MeV neutron released in a fission reaction loses half its energy in each moderator collision, how many collisions are needed to bring it to (1/25) eV?

Question

Quizplus · Accepted Answer

The energy of the neutron is halved with each collision. Starting from 2.0 MeV, the energy after n collisions is (2.0 MeV) * (1/2)^n. To find n when the energy is (1/25) eV, convert 2.0 MeV to eV (2.0 MeV = 2.0 x 10^6 eV) and solve (2.0 x 10^6) * (1/2)^n = 1/25. Solving for n gives approximately 26 collisions.

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