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

Question

Quizplus · Accepted Answer

To go from 2.0 MeV to (1/25) eV, we need to reduce the energy by a factor of (2.0 x 10^6)/(1/25) = 50 million. Since the energy is decreased by a factor of 2 in each collision, we need log2(50 million) ≈ 25.6 collisions, which we round up to 26. Therefore, the correct answer is C.

If a 20-MeV Neutron Released in a Fission Reaction Loses Half Its