Lesson 3.8.1.7

3.8.1.7 Induced fission Quiz: AQA Physics, Unit 8

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.8.1.7, Induced fission: 20 multiple choice questions for the AQA Physics (7408), Unit 8: Nuclear physics (A-level only), written with Revision Ninja.

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The 20 questions

  1. Which particle is absorbed by a uranium-235 nucleus to induce fission?

    • Fast proton
    • Alpha particle
    • Thermal neutron
    • Beta particle

  2. How many neutrons per fission must cause further fission for a self-sustaining chain reaction?

    • At least one
    • At least three
    • Zero
    • At least two

  3. What term describes the minimum mass of fissile material needed for a self-sustaining reaction?

    • Atomic mass
    • Critical mass
    • Mass defect
    • Rest mass

  4. What is the main function of a moderator in a nuclear reactor?

    • Absorb excess neutrons
    • Slow down neutrons
    • Cool the core
    • Generate electricity

  5. What is the main function of control rods in a nuclear reactor?

    • Absorb neutrons
    • Produce gamma rays
    • Transfer thermal energy
    • Slow down neutrons

  6. What is the main function of coolant in a nuclear reactor?

    • Prevent radioactive leakage
    • Slow down neutrons
    • Remove thermal energy
    • Absorb neutrons

  7. Why are light nuclei most effective as moderators in a nuclear reactor?

    • Large charge
    • High density
    • Neutron absorption
    • Similar neutron mass

  8. A neutron collides head-on and elastically with a stationary equal-mass nucleus. What is its final speed?

    • Zero
    • Half original speed
    • Double original speed
    • Unchanged speed

  9. A neutron collides head-on and elastically with a carbon-12 nucleus at rest. What fraction of its kinetic energy is retained? Use ((A-1)/(A+1))^2.

    • about 0.14
    • about 0.50
    • about 0.72
    • about 0.28

  10. Which element is commonly used to manufacture reactor control rods?

    • Uranium
    • Graphite
    • Boron
    • Water

  11. What state is a nuclear reactor in when its multiplication factor k equals 1.00?

    • Subcritical
    • Thermal meltdown
    • Supercritical
    • Critical

  12. What happens to power output when a nuclear reactor's multiplication factor k exceeds 1.00?

    • It drops to zero
    • It increases
    • It decreases
    • It remains constant

  13. Which isotope's proportion is increased when uranium fuel is enriched?

    • Plutonium-239
    • Uranium-238
    • Uranium-235
    • Thorium-232

  14. Which factor reduces the critical mass required for a fissile nuclear reactor core?

    • Neutron reflector
    • Impure fuel
    • Lower density
    • Higher temperature

  15. Why are fast neutrons slowed down by a moderator in a nuclear reactor?

    • Lower core temperature
    • Faster energy release
    • Higher fission probability
    • Reduced gamma radiation

  16. What is the primary function of the coolant in a thermal nuclear reactor?

    • Shield gamma rays
    • Remove thermal energy
    • Absorb excess neutrons
    • Slow down neutrons

  17. How can the rate of fission in a nuclear reactor core be increased?

    • Add coolant fluid
    • Remove the moderator
    • Insert control rods
    • Withdraw control rods

  18. Which isotope undergoes induced fission when absorbing thermal neutrons in a reactor?

    • Uranium-235
    • Plutonium-242
    • Uranium-238
    • Thorium-232

  19. A reactor releases 200 MeV per fission. How many fissions per second correspond to a power of 1 W? Use 1 MeV = 1.6 x 10^-13 J.

    • 3.1 x 10^6 per second
    • 2.0 x 10^8 per second
    • 3.1 x 10^10 per second
    • 3.2 x 10^11 per second

  20. Which components directly control the rate of neutron absorption in a nuclear reactor?

    • Concrete shields
    • Coolant pumps
    • Control rods
    • Fuel rods

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