Decay Modes, Decay Chains and Nuclear Reactions · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Which decay a nucleus chooses

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

  1. One alpha particle leaves a nucleus. How do mass and charge change?

    • Mass down 4, charge down 2
    • Mass unchanged, charge up 1
    • Mass down 1, charge unchanged

  2. A nucleus is neutron-heavy for its size. Which decay do you predict?

    • Alpha emission
    • Beta minus: a neutron becomes a proton plus an electron
    • Electron capture

  3. Gamma emission changes the mass number of the nucleus.

    Circle one:   True   False

  4. Polonium-210 (charge 84) alpha decays. Type the daughter's charge number.

    Answer: ______________

  5. Uranium-238 (charge 92) emits one alpha particle. What is the daughter?

    • Uranium-234 (92)
    • Protactinium-234 (91)
    • Thorium-234 (90)

  6. Potassium-40 captures an inner electron. What changes?

    • Mass down 4, charge down 2
    • Charge down one, mass unchanged
    • Charge up one, mass unchanged

  7. U-238 became Th-234 by alpha. Th-234 next decays with a 24-day half-life. Which particle leaves?

    • An electron
    • An alpha particle
    • A positron

  8. A student says beta electrons orbited the atom before release. What is wrong?

    • Electrons cannot leave atoms at all
    • Gamma rays always carry them away
    • The electron is created in the nucleus during decay
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Answer key

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

Which decay a nucleus chooses W1-mt_b_imidwJeQ-s1

  1. Mass down 4, charge down 2 · An alpha is two protons plus two neutrons, so both tallies drop together.
  2. Beta minus: a neutron becomes a proton plus an electron · Extra neutrons shed an electron as one converts to a proton, moving toward stability.
  3. False · Gamma only dumps leftover excitation energy, leaving mass and charge untouched.
  4. 82 · Charge 84 minus the alpha's 2 gives daughter charge 82.
  5. Thorium-234 (90) · Subtract 4 in mass and 2 in charge: 238 becomes 234, and 92 becomes 90.
  6. Charge down one, mass unchanged · A proton plus the electron becomes a neutron, so charge drops with mass steady.
  7. An electron · Th-234 beta decays to protactinium-234, releasing an electron.
  8. The electron is created in the nucleus during decay · The electron is produced at the decay moment, never parked in the nucleus beforehand.
Worksheet · LightMySky