Radioactivity

• Structure of an atom

  
• The alpha particle, scattering experiment

  
• Nuclear radiation strength

  
• Nuclear Radiation

  
• Types of nuclear radiation

  • Alpha (a)
  • Beta (ß)
  • Gamma (Y)
• What happens in an atom when electromagnetic radiation is absorbed

  An electron moves into a higher energy level further away from the nucleus
• What happens in an atom when electromagnetic radiation is emitted

  An electron moves into a lower energy level closer to the nucleus
• The radius of an atom is more than 10,000 times bigger than the nucleus radius
• Radioactive decay isn’t a random event - you can't predict or influence when it will happen
• A radioactive substance contains unstable nuclei that become stable by emitting radiation
• Electrons are 1/2000 the mass of a proton or neutron
• Mass number


  Protons + neutrons
• Isotope

  Same atomic number (protons) and different mass number (protons + neutrons)
• Plum pudding model

  Negatively charged ions embedded in a sphere
• Nuclear model

  Positively charged nucleus surrounded by negatively charged electrons
• Models change as new evidence is obtained that doesn't support the current model
• Alpha particle scattering experiment

  Some alpha particles deflected and a few repelled back, leading to the nuclear model replacing the plum pudding model
• Particle ranges

  • Alpha particle range: <5cm
  • Beta particle range: 1m
  • Gamma particle range: very large
• Particle shielding

  • Alpha stopped by skin and paper
  • Beta stopped by thin metal sheet
  • Gamma stopped by thick lead
• Ionising power

  • Alpha: High
  • Beta: Low
  • Gamma: Very low
• Nuclear radiation detection

  GM tube measures count rate when connected to a rate meter
• Calculating half-life

  Measured count rate drops from 1600 to 200 so it is 3 half lives which is 6 days, so half-life is 6/3 = 2 days
• Calculating net decline after 45 hours for dubnium-270 with 15 hour half-life

  45 hours is 45/15 = 3 half-lives, so net decline is 1/2 x 1/2 x 1/2 = 1/8
• Radioactive contamination

  Unwanted direct contact with materials containing radioactive atoms, causing the exposed object to become radioactive
• Irradiation

  Exposing an object to nuclear radiation without the object becoming radioactive
• Contamination hazard

  Depends on type of radiation, ionising power, and ability to penetrate
• Irradiation hazard

  Depends on distance from source and time of exposure
• Suitable precautions must be taken to protect against radiation hazards
• The effect of radiation on humans is studied globally and findings are published for peer review
• Half life count

  Dividing by half (1600,800,400,200)3 half life counts (3 divisions from 1600 to 200)