In a thermal nuclear fission reactor, fast-moving neutrons produced in fission reactions must be slowed down to thermal speeds by a moderator to sustain the chain reaction.
Which of the following statements correctly explains the physical principles governing the choice of moderator and the moderation process?
Moderator nuclei should have a low mass number AAA to maximize the kinetic energy transferred from the neutron per elastic collision, and a low neutron capture cross-section.
Moderator nuclei should have a high mass number AAA so that their greater inertia allows them to absorb more kinetic energy during elastic collisions.
The moderator must consist of elements with a high atomic number ZZZ to decelerate the neutrons via Coulomb scattering with the highly charged nuclei.
The moderator slows neutrons down by capturing them, leading to a rapid beta-minus decay that re-emits a neutron of lower kinetic energy.
