Which of the following statements provides the correct physical explanation for the role of the moderator in this process?
It absorbs high-energy gamma photons produced during fission, converting their energy into heat to raise the temperature of the coolant.
It slows down the fast-moving neutrons produced in fission to thermal speeds, thereby increasing the probability of their capture by Uranium-235 nuclei.
It acts as a physical barrier that prevents neutrons from escaping the reactor core, reflecting them back into the fuel rods.
It increases the kinetic energy of slow neutrons so they can overcome the electrostatic repulsion of the positively charged Uranium-235 nuclei.
128 exam-style questions on AQA A Level Physics Radioactivity (A-level only), covering Rutherford scattering (A-level only), $\alpha$ , $\beta$ and $\gamma$ radiation (A-level only), Radioactive decay (A-level only), Nuclear instability (A-level only), Nuclear radius (A-level only), Mass and energy (A-level only), Induced fission (A-level only), and Safety aspects (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.