Atomic Structure

• Atomic theory said that everything is made up of particles that can't be broken down, and that the particles are separated by empty space.
• John Dalton said that atoms are solid spheres and that different spheres made up the different elements.
• JJ Thomson said that atoms are a ball of positive charge with negative electrons scattered throughout.
• Rutherford conducted the alpha scattering experiment.
• Alpha scattering:

  • Fired alpha particles at gold
  • Expected particles to pass straight through but some were deflected
• Rutherford came up with the nuclear model after his experiments. This model said that there was a positive nucleus at the centre of the atom, and that it was surrounded by a "cloud" of electrons.
• Bohr said that electrons orbited the nucleus in shells. These shells prevent the atom from collapsing.
• Chadwick discovered the neutron.
• The nucleus contains protons and neutrons.
• The number of protons determine what element it is.
• Electrons orbit the nucleus in shells.
• If electrons gain energy from electromagnetic radiation, they become excited and go to a higher energy level.
• After electrons have gone to a higher energy level, they soon fall to a lower one again and release energy as electromagnetic radiation.
• Isotopes are atoms with the same number of protons but a different number of neutrons.
• Unstable isotopes decay by emitting radiation.
• Ionisation means that electrons leave atoms.
• Radioactive materials consist of unstable isotopes that can decay.
• Alpha particles:

  • Helium nucleus
  • Positive charge
  • Travel a few centimetres in air, stopped by a sheet of paper
  • Largely ionising because of their size and charge
• Beta particles:

  • Fast moving electron
  • Neutron decays into a proton and an electron
  • Moderately ionising
  • Stopped by 5 mm of aluminium
• Gamma radiation:

  • Electromagnetic radiation waves
  • Pass through materials
  • Weakly ionising
  • Stopped by lead or concrete
• In alpha decay:

  • Mass number = -4
  • Atomic number = -2
  • Atomic number changes = new element
• In beta decay:

  • Mass number = same
  • Atomic number = +1
• In gamma decay:

  • Pure energy means that the mass number and the charge stay the same
• Neutron emission:

  • Mass number = -1
• The decay process is completely random. We cannot tell when a nucleus will decay or which one will decay.
• The activity is the overall rate of decay of all isotopes in a sample.
• Activity is measured in becquerels (Bq).
• 1 bq = 1 decay per second
• The half life is the time taken for the number of radioactive nuclei to halve, OR the time taken for the number of decays (activity) to halve.
• Overtime, the number of unstable particles decreases, which means that the activity decreases.
• Fewer radioactive nuclei means a lower activity.
• Irradiation is the exposure to radiation.
• Contamination is where radioactive particles get on an object.
• With contamination, particles are likely to decay and irradiate you.
• Ionising radiation is typically the most dangerous
• Ionising radiation is typically the most dangerous because it can enter living cells and interact with molecules inside. It can ionise DNA and cause mutations.
• Outside of the body, gamma radiation is the most dangerous.
• Inside/on the body, alpha particles are the most dangerous.
• The dosage of radiation depends on:

  • distance from the source
  • Time exposed to the radiation
  • How radioactive the source is
• How we minimise irradiation:

  • Wearing gloves
  • Handle radioactive substances with tongs
  • Store sources in a lead lined box