p7: radioactivity

• Radioactivity is the spontaneous breaking down of atoms
• Three main types of radiation

  • Alpha
  • Beta
  • Gamma
• Atoms have a nucleus with protons, neutrons, and electrons
• Gold foil experiment


  Experiment carried out by Ernest Rutherford that discovered the positive nucleus and small size of the atom
• Alpha emission

  1. Helium nucleus released from parent nucleus

  2. Mass number decreases by 4

  3. Proton number decreases by 2
• Alpha emission examples


  • Radon-226
  • Uranium-235
• Beta emission

  1. Neutron converted to proton

  2. Proton number increases by 1

  3. Atomic mass stays the same

  4. Beta particle (high energy electron) released
• Beta emission example


  • Carbon-14
• Gamma emission

  1. Electromagnetic wave released

  2. Proton and atomic mass do not change
• Gamma emission example

  • Neon-22
• Alpha radiation


  • Least penetrating
  • Most ionizing
• Beta radiation

  • Medium penetration
  • Medium ionization
• Gamma radiation


  • Most penetrating
  • Least ionizing
• Isotope

  Different form of an atom with same protons and electrons but different neutrons
• Heavier isotopes are more likely to undergo radioactive emission
• Half-life


  Time required for half the radioactive nuclei to decompose
• Half-life is constant for a given radioactive isotope
• Using half-life to predict remaining radioactive nuclei

  1. After 1 half-life, 1/2 remain

  2. After 2 half-lives, 1/4 remain

  3. After 3 half-lives, 1/8 remain, etc.
• Nuclear fission in reactors uses uranium-235 undergoing alpha emission to start a chain reaction
• Nuclear fission has benefits like not releasing greenhouse gases, but also produces dangerous nuclear waste
• Nuclear fusion could provide abundant energy, but is very difficult to achieve on Earth due to the extreme temperatures required
• Hydrogen bombs demonstrate nuclear fusion, but it is uncontrolled and not viable for industrial-scale energy production