Radioactivity

• 3 main models of the atom

  • Need to know the experiment that led to the discovery of the nucleus (the foil experiment)
• Foil experiment

  1. Alpha particles fired at thin sheet of gold foil

  2. Most passed through, some rebounded back more than expected
• Atom model 1

  Positive sphere with negative electrons inside, whole atom is neutral
• Atom model 2

  Positive nucleus, negative electrons orbiting
• Atoms must have a positive nucleus (based on foil experiment)
• 3 types of radiation

  • Alpha
  • Beta
  • Gamma
• Alpha radiation

  • Unstable nuclei emit alpha particles (2 protons, 2 neutrons)
  • Strongly ionizing
• Beta minus radiation

  Electron released from nucleus (neutron decays into proton, electron, neutrino)
• Beta plus radiation

  Proton decays into neutron, positron (anti-particle of electron) released
• Gamma radiation

  Energy released by decaying nucleus, electromagnetic wave, weakly ionizing
• Penetration of different types of radiation

  • Alpha stopped by paper/skin
  • Beta stopped by aluminium
  • Gamma stopped by lead
• Writing nuclear equations

  Show atom before, arrow, atom after, radiation emitted
• Alpha decay

  Mass number decreases by 4, atomic number decreases by 2 (element changes)
• Beta minus decay

  Mass number stays same, atomic number increases by 1
• Beta plus decay

  Mass number stays same, atomic number decreases by 1
• Radiation is happening around us all the time (background radiation)
• Measuring radiation

  Use a special tube that clicks when it detects radiation
• Sources of background radiation

  • Radon gas
  • Medical processes
  • Internal (food, body processes)
• Radiation decay is random, can only predict half-life (average time for half to decay)
• Half-life

  Time for half the radioactive nuclei to decay
• Uses of radiation

  • Medical (x-rays, sterilization)
  • Can also cause mutations and cancer
• Nuclear fission

  Neutron fired at large nucleus, splits into two smaller nuclei, releases more neutrons to continue chain reaction
• Nuclear fusion

  Small nuclei collide at high speeds, fuse into larger nucleus, releases energy