atomic structure

• plum pudding model:

  • cloud of positive charge
  • negative particles floating within it
• current model:

  • nucleus at the centre
  • discovery of neutron proton and electron
  • mostly empty space
  • electrons orbiting on energy levels
• rutherfords alpha scattering:

  • alpha particles fired at the centre of an atom
  • fired at 1 cell thick of gold foil
• results of the alpha scattering:

  • most particles travelled straight through
  • some were deflected
  • some were deflected significantly
• conclusions of the alpha scattering:

  • atom is mostly empty space
  • small mass in the centre
  • mass must be positive because of the repulsion force
• what is an isotope?

  • same number of protons
  • different number of neutrons
  • charge doesn't change, but mass does
• what is an ion?

  • same number of protons
  • different number of electrons
  • charge changes, but mass doesn't
• features of alpha radiation:

  • emitted from a nucleus
  • strongly ionising
  • doesn't travel in air
  • stopped by paper
  • using in smoke detectors
• features of beta:

  • fast moving electron released by the nucleus
  • moderately ionising
  • travels further in air
  • stopped by aluminium
  • used in material thickness testing
• features of gamma:

  • electromagnetic wave released by the nucleus
  • weakly ionising
  • travels far in air
  • stopped by lead
  • used in sterilising equipment
• what is a half-life?

  time taken for the number of radioactive nuclei to half
• features of half-lifes:

  • radioactive sources give out radiation as it decays
  • measured with a geigmer-muller counter
  • random process
  • activity is the rate at which the source decays
• what is irradiation?

  Exposure to ionizing radiation.

  • comes from beta and gamma
  • can be protected by lead
• what is contamination?

  radioactive particles getting onto objects

  • risk from alpha
  • can be protected by wearing protective gear e.g. suite/gloves