In a nuclear reactor, fast neutrons released from the fission of uranium-235 must be slowed down (moderated) to become thermal neutrons to sustain a controlled chain reaction.
Suppose a fast neutron is released with a kinetic energy of E0=2.0 MeVE_0 = 2.0\text{ MeV}E0=2.0 MeV. It must be moderated to a thermal energy of Ef=0.032 eVE_f = 0.032\text{ eV}Ef=0.032 eV or lower. Assuming the neutron loses exactly 50% of its remaining kinetic energy during each elastic collision with a moderator nucleus, what is the minimum number of collisions required for the neutron to become thermal?
6
16
20
26