Fission Reactors and Fusion in the Laboratory · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Splitting atoms and fusing them

Science · Quantum & Modern Physics · ages 20-21
Name ______________________   Date ____________

  1. What is the moderator's job in a reactor?

    • Speed neutrons up for harder hits
    • Slow neutrons so fission stays likely
    • Absorb all neutrons to stop fission

  2. What comes out of a uranium-235 fission?

    • Two lighter fragments plus neutrons and energy
    • One heavier nucleus plus a positron
    • Only heat with no particles

  3. Control rods absorb surplus neutrons to steady the chain reaction.

    Circle one:   True   False

  4. Why must fusion fuel be so extremely hot?

    • Speed to overcome electrical repulsion and touch
    • Heat to boil off extra neutrons
    • Fire to burn away impurities

  5. What does criticality mean?

    • Every neutron escapes the fuel
    • The fuel melts from its own heat
    • Exactly one new fission per fission on average

  6. Uranium-235 plus 1 neutron splits into barium-141, krypton-92, and neutrons. Type how many neutrons leave.

    Answer: ______________

  7. Which route gives more energy per kilogram with less long-lived waste?

    • Fission
    • Chemical burning
    • Fusion

  8. A student says hot fuel alone guarantees fusion power. What is missing?

    • A stronger magnetic compass
    • Confinement time for dense fuel
    • Colder walls around the plasma
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Splitting atoms and fusing them W1-mt_iTwgXI0iBy-s1

  1. Slow neutrons so fission stays likely · Slow neutrons split uranium far more readily than fast ones.
  2. Two lighter fragments plus neutrons and energy · The split nucleus yields two fragments, spare neutrons, and released energy.
  3. True · Cadmium rods swallow extras so exactly one new fission follows each fission.
  4. Speed to overcome electrical repulsion and touch · Only violent thermal speed lets repelling nuclei reach each other.
  5. Exactly one new fission per fission on average · One-for-one replacement holds the chain steady instead of dying or racing.
  6. 3 · Mass numbers balance: 236 in, 233 in fragments, leaving 3 neutrons.
  7. Fusion · Fusion wins per kilogram and skips actinide waste, though it is harder to sustain.
  8. Confinement time for dense fuel · Temperature, density, and time must pass the bar together.
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